Online number:
Total visits:

Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
Display Method:
Application of Sand Filling Staged Fracturing Technology in Shale Oil Horizontal Wells with Deformed Casings
WANG Jingang, SUN Hu, REN Bin, YIN Junlu
 doi: 10.11911/syztjs.2021084
[Abstract](19) [FullText HTML](5) [PDF 6444KB](10)
In view of the situation that horizontal wells can meet the pressure bearing requirements but cannot be run into conventional fracturing tools due to casing deformation, in order to achieve the purpose of reservoir selective and large-scale fracturing, based on the principle of staged fracturing technology of sand filling in horizontal wells, the ultimate sand filling is used to form the sand plug in the fracture, so as to effectively seal the reformed intervals. Two sand filling modes, "tail-sand filling" and "fracture-blowing", are formed, which can realize the rapid and effective implementation of sand filling section in horizontal Wells. The field test results show that the sand-filling isolation segment is based on relative throttling rather than absolute closure, and the instantaneous overpressure appears when the pump is started with a minimum displacement, and the rupture pressure of each scetion is different, so the plugging effect is reliable. This process has outstanding advantages, such as high safety, low operation cost, well bore disposal after operation and wellbore integrity. In the H40 platform of shale oil in Changqing Oilfield, there are 8 stages of sand-filling fracturing, and the construction success rate is 100%. The successful implementation has filled the technological blank of sand-filling staged fracturing for shale oil horizontal Wells in Changqing area.
Drilling Fluid Technology for Horizontal Shale Oil Wells in Dagang Oilfield
TIAN Zengyan, YANG Hewei, LI Xiaohan, YIN Li, WANG Xin, HUANG Chen
 doi: 10.11911/syztjs.2021012
[Abstract](32) [FullText HTML](11) [PDF 1806KB](17)
BH-KSM-Shale and BH-WEI-Shale drilling fluids were developed to solve the technical problems of wellbore stability, borehole cleaning, lubrication and anti-sticking in the horizontal shale oil section of Cangdong and Qikou in Dagang Oilfield. The plugging ability of drilling fluid can be improved by using reasonable material size ratio and proper fiber material, and the effect of sand carrying and hole cleaning can be enhanced by increasing the dynamic plastic ratio and viscosity of low shear rate. The results showed that the dynamic plastic ratio of the two systems can reach more than 0.35, the Kf was reduced by 40%, and the permeability plugging filtration was less than 15 mL. The technology has been applied in 36 wells such as GD1701H, QY2H, etc. with the maximum hole diameter expansion rate of 8.67%, which solved the technical problems of wellbore stability, borehole cleaning, lubrication and anti-sticking problems effectively in the development of horizontal wells in shale oil formation. The results showed that two sets of proprietary technologies can meet the needs of shale oil horizontal well developments in Dagang Oilfield.
Progress and Developing Suggestions of Sinopec Multi-Stage Horizontal Well Fracturing Technology for Shale Oil
JIANG Tingxue, WANG Haitao
 doi: 10.11911/syztjs.2021071
[Abstract](30) [FullText HTML](22) [PDF 1594KB](10)
Volume fracturing technology of horizontal well is the key technology to realize efficient development of shale oil formation, which is different from shale gas fracturing technology. It is of practical significance to carry out follow-up research on fracturing technology according to the characteristics of domestic shale oil reservoir. This paper investigates the development of horizontal well fracturing technology of shale oil and related basic research, compares the differences of engineering characteristics and geological characteristics of shale oil at home and abroad, analyzes and puts forward the requirements and challenges of shale oil fracturing technology of Sinopec. Based on this, in view of the difficulties of reservoir reconstruction in typical shale oil blocks of Sinopec, such as high clay content, strong water sensitivity and stress sensitivity, strong plasticity et al., the development suggestions for medium/high maturity shale oil and medium/low maturity shale oil are put forward from the perspective of integrated research and implementation of geology development engineering by considering economy and field operability. The relevant technology development strategies should be coordinated with the corresponding incentive industrial policies, which can be designed as a whole and implemented step by step. It is expected that the break even oil price will be greatly reduced, and then the stable production level and economic development effect of domestic shale oil will be greatly improved.
Fracturing Technology of Horizontal Well in Jimusaer Shale Oil Second Class Area
CHEN Chaofeng, WANG Bo, WANG Jia, XU Yiwen, QIN Yingmin, LI Xuebin
 doi: 10.11911/syztjs.2021089
[Abstract](38) [FullText HTML](14) [PDF 2295KB](12)
In order to solve the problem of horizontal well production increase caused by low fluidity and limited fracture height of shale reservoir, the effective production technology of Jimusaer shale oil-bearing second-class reservoir in Junggar basin was explored, and the key technology research was carried out to improve the fracture control degree by dense cutting transformation and increase the longitudinal utilization degree by thin interbedding. The average cluster spacing is reduced to 13.6 m, which greatly improves the fracture control degree of shale reservoir; It improves the displacement and the amount of gel used in the vertical well fracturing operation, verifies the feasibility of crossing the formation in xiadeshi class II reservoir, and forms the key technologies of crossing the formation, such as large displacement of horizontal well 12–14 m3/min, multi slug pumping of gel and slick water, multi-scale support of medium and small particle size, 2.7 m3/m high sanding strength, etc., which ensure the effective support of bedding turning fractures. The field test shows that the technology can effectively improve the fracture control degree of volume fracturing in horizontal wells, and the cumulative oil production of horizontal wells in type II reservoir test exceeds 9 183 t in one year, which is more than three times of that of previous horizontal wells. The research results show that the horizontal well dense cutting through layer fracturing technology can effectively solve the production problem of multiple thin oil layers in the second class reservoir, and provide a technical way for the horizontal well fracturing production in the second class area of shale oil.
Accelerating technology of horizontal well drilling in large shale oil cluster in Changqing Oilfield
NI Huafeng, YANG Guang, ZHANG Yanbing
 doi: 10.11911/syztjs.2021076
[Abstract](15) [FullText HTML](3) [PDF 1614KB](6)
In Changqing shale oil large well cluster, horizontal Wells are increasing year by year and the number of Wells is increasing year by year. There are many serious problems, such as high skew ratio, large displacement, three-dimensional wellbore trajectory, stress buckling of drilling tools, large friction and torque during drilling, sliding drilling support pressure, horizontal fault loss, and low recognition degree near drill bit in reservoir. Therefore, the key technologies such as multi-layer layout design of horizontal well in large shale oil cluster, lithology analysis of Chang 7 reservoir, 3D wellbore trajectory control, and matching test of accelerating tools have been studied, and the accelerating technology of horizontal well in large shale oil cluster in Changqing has been formed. Field tests were carried out in three large well clusters, such as H40 and H60 in China. The number of horizontal Wells in the largest cluster reached 31, and the average drilling cycle was 18.9 days, which was shortened by 7.5%. The research and test show that the large-scale development of Changqing shale oil has been realized by the large cluster horizontal Wells, and the construction pace of Longdong National Shale Oil Demonstration Base has been accelerated.
Numerical Simulation of the Brittleness Index of Anisotropic Laminated Argillaceous Limestone Facies Shale in the Jiyang Depression
JIA Qingsheng, ZHONG Anhai, ZHANG Zilin, DING Ran
 doi: 10.11911/syztjs.2021086
[Abstract](24) [FullText HTML](16) [PDF 2193KB](17)
Argillaceous limestone facies core samples were drilled from Well Fanye X to reveal the brittleness index for anisotropic shale from the upper Chun submember of the fourth member of Shahejie Formation in the Northern Boxing Subsag of the Jiyang Depression. With the laboratory measured stress–strain curves for rocks as the calibration criterion, a three-dimensional numerical simulation was adopted to calculate and analyze the Poisson’s ratio, Young’s modulus and strength parameters of the cores. Four typical methods were employed to calculate the brittleness index of all cores. Research demonstrates that as the confining pressure increases, the degree of anisotropy of mechanical parameters declines, and the anisotropy of elastic parameters is more sensitive to the variation in confining pressure than that of strength parameters. Therefore, it is recommended that the brittleness and anisotropy of core mechanics with elastic parameters. The brittleness index calculation model based on the principle of conservation of energy can objectively evaluate the shale core brittleness. The brittleness index decreases significantly as the confining pressure grows, and it first drops and then rises as the bedding dip increases. In other words, the brittleness index in the direction close to the angle of internal friction is the lowest, while relatively higher in the 0° and 90° coring directions. The research results can provide a theoretical basis for evaluating fracturing feasibility in shale oil reservoirs and selecting wells and layers in the Jiyang Depression.
Research on Interlayer Interference and Fracture Propagation Law of Shale Oil Reservoir in Dongying Sag
MENG Yong, JIA Qingsheng, ZHANG Liaoyuan, ZHENG Bintao, DENG Xu
 doi: 10.11911/syztjs.2021094
[Abstract](11) [FullText HTML](7) [PDF 2831KB](7)
The Dongying Sag of Shengli Oilfield has abundant shale oil reserves, but the physical properties of the reservoirs are poor. The vertical strata are many and thin, mostly interbedded with limestone and mudstone. In order to accurately describe the propagation law of hydraulic fractures in shale oil reservoirs and the interlayer stress interference mechanism, a multi-thin interbedded layered fracturing model based on the coupling of seepage-stress-damage was established according to the nonlinear finite element method. And finally optimized the fracturing construction parameters. The simulation results show that with the expansion of hydraulic fractures, the stress interference area will become larger and larger. When the displacement is 9~12 m3/min and the viscosity is 20 mPa∙s, the induced stress at the tip of the fracture is large, and it is easy to connect to natural fractures and fracturing. The transformation effect is obvious; when the thickness of the upper interlayer is greater than 2.5 m and the lower interlayer is greater than 4.5 m, the phenomenon of interlayer is rarely seen. The simulation results provide certain theoretical support for the subsequent hydraulic fracturing construction of shale oil reservoirs in Dongying Depression.
Numerical Simulation of Multiphase Flow in Fracture Network of Shale Oil Reservoir
XIAN Yuxi, CHEN Chaofeng, FENG Meng, HAO Youzhi
 doi: 10.11911/syztjs.2021090
[Abstract](25) [FullText HTML](9) [PDF 2198KB](12)
Multiphase flow model embedded in fractures and multiphase flow model in multi-fracture cross network are developed to accurately simulate the fluid flow in complex fractures of shale oil reservoir, and numerical simulation calculation method is presented for analyzing the flow of multiphase fluid in multi-fracture cross network. The numerical simulation results show that the formation pressure in the numerical simulation results directly represents the degree of the pressure variation in the area around the fracture network with production time. The numerical simulation method of multiphase seepage in fracture network solves the problems of single fluid, large fracture scale range, high precision of mesh division, discontinuous fluid parameters at fracture interface, etc. It can also determine the scale and distance of communication between hydraulic fracturing fractures and natural fractures. The results provide a scientific basis for the evaluation of shale oil reservoirs.
Key Development Fields and Technical System Construction of Lacustrine Shale Oil Surface Logging
WANG Zhizhan, DU Huanfu, LI Xiangmei, NIU Qiang
 doi: 10.11911/syztjs.2021093
[Abstract](25) [FullText HTML](10) [PDF 1609KB](14)
The lacustrine shale oil has just started in China, as the link of the integration of geology and engineering, the key development fields of surface logging are not clear yet, and the corresponding acquisition and evaluation technology system has not been systematically established. To some extent, the development of shale oil surface logging technology and the full play of surface logging function are restricted. On the basis of system analysis shale oil surface logging technology present situation and the integration demands of shale oil geology and engineering, the evaluation contents, technical difficulties and shortcomings of of surface logging are analyzed from four aspects: quantitative analysis of mineral components and identification of favorable lithofacies while drilling, evaluation of reservoir property and oil-bearing property, evaluation of mobility, evaluation of drillability. Three key fields of development are put forward: diffuse reflection Fourier transform infrared spectroscopy (DRIFTS), drilling fluid oil-bearing NMR online surface logging, T1-T2 two-dimensional NMR logging of rock samples, and rock mechanics of surfce logging. On this basis, in accordance with the principle of pertinence, effectiveness and economy, the surface logging technology system based on the evaluation of reservoir property, oil content, mobility, compressibility and drillability is established, which has a guiding significance for the direction of scientific research and production practice of shale oil surface logging.
Numerical simulation of oil displacement by fracturing imbibition in shale oil horizontal wells
OUYANG Weiping, ZHANG Mian, SUN Hu, ZHANG Yunyi, CHI Xiaoming
 doi: 10.11911/syztjs.2021083
[Abstract](65) [FullText HTML](41) [PDF 2032KB](21)
In order to improve the production prediction accuracy of fracturing imbibition displacement in shale oil horizontal wells, optimize parameters such as shut-in time and fracturing fluid volume, a mathematical model of oil-water two-phase flow in the whole process of fracturing fluid injection, well shut-in imbibition and well opening production was established. The control volume finite element method was used to solve the model, and the process of oil-water displacement between matrix and fracture by imbibition was simulated. The dynamic changes of oil-water pressure field, velocity field, production and water content were obtained. Characteristics of fracturing imbibition displacement were analyzed. The shut-in time and fracturing fluid volume were optimized. Influence of matrix permeability and fracture network complexity were studied. The results show that the larger the capillary force is or the longer the shut-in time is, the lower the water content is and the more obvious the imbibition stimulation effect is. Increasing the volume of fracturing fluid can improve the oil displacement production by imbibition, but at the same time it will cause the increase of water content. The reasonable volume of fracturing fluid can be determined by the increase of water content and production. The reasonable shut-in time is affected by capillary force, matrix permeability and fracture network complexity, in which capillary force and matrix permeability determine the imbibition speed, while fracture network complexity determines the imbibition area. The established oil-water two-phase seepage model can provide technical support for the optimal design of shale oil fracturing.
Key Drilling Techniques for the Ultra-long Horizontal Section of Horizontal Wellsin the Shale Oil Reservoir in Jimusaer, Xinjiang
CHEN Haiyu, WANG Xindong, LIN Jing, CHEN Tao, LI Hui, FAN Lin
 doi: 10.11911/syztjs.2021036
[Abstract](87) [FullText HTML](26) [PDF 2087KB](43)
Borehole instability and excessive friction were encountered during drilling the ultra-long horizontal section of horizontal wells in the shale oil reservoir in Xinjiang. For safe and fast drilling of horizontal sections of 3,000–3,500 m, a friction reduction study was performed, such as optimization of the casing program, design of a dual two-dimensional trajectory, and determination of drilling parameters based on wellbore cleaning condition. Moreover, an oil-based drilling fluid formula with excellent performance in inhibition, stability and lubricity was identified in the laboratory. Finally, the key techniques were developed for the ultra-long horizontal section of horizontal wells in the shale oil reservoir in Jimusaer, Xinjiang. The techniques were applied in three wells with a penetration rate of 10.9 m/h in the horizontal section and greatly reduced drilling time. The drifting process, electric logging and casing running in those wells were all successful in one run, without downhole complex situations presented during drilling and completion. It set the longest horizontal section record of unconventional oil and gas reservoirs in China. Research and application results show that the techniques can meet the technical requirements for safe and efficient drilling in the ultra-long horizontal section of the horizontal wells in the shale oil well area in Xinjiang and further improve the extension capacity of the horizontal section, and it is worthy of popularization and application.
Present Status and Development Prospects of Sinopec Shale Oil Engineering Technology
ZHANG Jinhong
 doi: 10.11911/syztjs.2021072
[Abstract](69) [FullText HTML](23) [PDF 1521KB](38)
Depending on the characteristics of continental shale oil reservoirs and the demands of exploration and development, Sinopec has successfully applied new technologies to 17 exploratory wells. The new technologies are in the area of optimized and fast drilling and completion, logging evaluation, and reservoir stimulation. These technologies strongly support the exploration and development evaluation of continental shale oil in a number of regions, such as Jiyang Depression, Biyang Sag, and Sichuan Basin, and make a major breakthrough in the exploration of shale oil in Jiyang Depression. However, the shale oil engineering technology of Sinopec still lags behind those of some other countries. Therefore, further research is needed in technologies of multi-layer-series development by shale oil well factory drilling, geosteering horizontal wells with ultra-long horizontal sections, and integration of shale oil geology and hydraulic fracturing. Sinopec’s research strives toward the perfection of the shale oil engineering technology system, the improvements in quality, speed, efficiency, and output, and the beneficial development of continental shale oil.
Technical Status and Suggestions for Shale Oil Reservoir Stimulation at Home and Abroad 
CHEN Zuo, LIU Honglei, LI Yingjie, SHEN Ziqi, XU Guoqing
 doi: 10.11911/syztjs.2021081
[Abstract](39) [FullText HTML](32) [PDF 1623KB](28)
North American marine shale oil has witnessed large-scale commercial development by means of volumetric fracturing with tight spacing in long horizontal section wells, following best practices for “industrialized” construction or “factory drilling,” etc. However, the exploration and production of continental shale oil in China started late and can be said to still be generally in the stage of experiment and demonstration. To accelerate the exploration and production process of shale oil in China and improve the appropriate implementation of relevant technology, this paper summarizes and analyzes the basic reservoir properties of North American marine shale oil and China’s continental shale oil reservoirs as well as the technical status and characteristics of reservoir stimulation. This study has resulted in many new insights. Given the unique properties of continental shale oil reservoirs with medium–high maturity in China, recommen-dations were made that would result in better production results for continental shale oil reservoirs with medium–high maturity in China. The recommendations focused on strengthening basic and mechanism research, addressing technical problems of cross layer fracturing in multi-lithology plastic reservoirs and complex fracture networks based fracturing, developing multifunctional fracturing fluid and pressure-sensitive intelligent proppant, studying drainage and CO2 injection and production technology, and tackling key problems of fracturing-flooding-producing integration.
Technology for Preventing and Controlling Circulation Loss in the Jimusaer Shale Oil Block
ZHOU Shuangjun, ZHU Lixin, YANG Sen, MAO Jun, LI Xiaojie, HUANG Weian
 doi: 10.11911/syztjs.2021034
[Abstract](26) [FullText HTML](15) [PDF 1499KB](16)
To address the problem of frequent circulation loss during the drilling of the Jimusaer shale oil block, an analysis of the relevant mechanism was conducted from the perspectives of stratigraphic distribution, lithological differences, and reservoir development characteristics. The circulation loss in this block was mainly concentrated in the Jurassic Badaowan Formation and the Permian Wutonggou Formation. The glutenite pores were developed in the shallow loss formation with loose cementation, while the induced fractures occurred in the deep loss formation. The circulation loss can be divided into the permeable type and the induced fracture type. Depending on its mechanism and the experience of dealing with it in the Jimusaer shale oil block, the matching principle between plugging materials and the circulation loss rate was formulated and prevention and control countermeasures were proposed. As a result, the technology to prevent and control circulation loss was developed for the Jimusaer shale oil block. It reduced the incidence of circulation loss from 38.00% to 19.70% and enhanced the success rate of plugging to 75% in the block. This indicates that the proposed technology is effective for tackling the problem of frequent circulation loss in the Jimusaer shale oil block and provide technical support and suggest best practices for the development of this block.
The Drilling Technology of Long Offset of 3D Horizontal Wells in Longdong Shale Oil Construction Area of Changqing Oilfield
TIAN Fengjun, WANG Yungong, TANG Bin, LI Zhijun, LIU Keqiang
 doi: 10.11911/syztjs.2021079
[Abstract](30) [FullText HTML](19) [PDF 1496KB](17)
In the eastern Gansu shale oil construction area of Changqing Oilfield, there are many gullies, water resources, basic farmland and forest resource protection areas. The development of horizontal Wells is greatly affected by topography and landform as well as resource protection areas. The offset of three-dimensional horizontal Wells directly affects the number of horizontal platform well number and factory operation, and affects the effective utilization of underground resources. By optimizing profile design, optimizing build points, eliminating offset and azimuth, improving wellbore trajectory control, and optimizing conventional screw drills and PDC bits without the use of rotary steerable systems, With the comprehensive application of friction and drag reduction tools and water-based CQSP-4 drilling fluid system suitable for large offset drilling of shale oil, the three-dimensional horizontal drilling technology for large offset drilling of shale oil in Changqing was formed. The technology has been applied to 6 long offset 3D horizontal Wells above 900 m in Longdong shale oil area, and the friction torque is obviously reduced. The drilling process is safe and efficient, and a good field application effect has been achieved. The successful application of this technology supports the efficient factory development of Longdong shale oil platform with multi-layer system and multi-rig, and also supports the transformation of drilling rig operation mode from single machine and single team to factory cluster. Six three-dimensional horizontal Wells with large offset above 900 m were successfully completed with this technology, and the HH60-1 horizontal well had an long offset of 1 102 m and reached 2 000 m in the horizontal section. This technology is beneficial to support the efficient factory development of eastern Gansu shale oil platform with multi-layer system and multi-rig, and supports the transformation of drilling rig operation mode from single machine and team to factory cluster.
The Technology of Snubbing Operation in Shale Oil Horizontal Wells in Cangdong Sag
WANG Dong, LAI Xueming, TANG Qing, ZHOU Junjie
 doi: 10.11911/syztjs.2021077
[Abstract](16) [FullText HTML](13) [PDF 1733KB](6)
Shale reservoir in Kong-2 member in Cangdong sag is extra-low pore and permeable, which has high clay minerals content. So it is easy to be contaminated by extraneous fluid during downhole operation. In order to maximum protect shale reservoir during pumping down operation, optimized sucker rod pump and ESP production string and downhole tools, which are conventionally used in shale oil. Formed snubbing operation technology such as blowout preventive tools, controllable bridge plug completion string, cable-laid coiled tubing operation, which effectively solve lined tubing cannot effectively seal, ESP cable can't put into well with pressure, etc. Field tests show that these can achieve zero reservoir contaminate during pumping down operation, and does not need to wait for pressure complete release.
Key Technologies for Drilling and Completing Horizontal Shale Oil Wells in the Jiyang Depression, Shengli Oilfield
HAN Laiju, YANG Chunxu
 doi: 10.11911/syztjs.2021073
[Abstract](47) [FullText HTML](19) [PDF 1717KB](22)
Since the geological conditions of the shale oil reservoir in the Jiyang Depression are complex, there are many technical difficulties during the drilling and completion of horizontal wells, such as high safety risk, low rate of penetration (ROP), low efficiency of wellbore trajectory control, high complex efficiency, and poor cementing quality. The key technologies for the drilling and completion of horizontal shale oil wells in the Jiyang Depression were preliminarily developed, benefiting from the exploration and integrated application of optimization design of drilling engineering, ROP and efficiency enhancement for the horizontal wells, development of high-performance synthetic base drilling fluid, and cementing quality improvement of the horizontal wells. Moreover, these technologies were successfully applied to eight horizontal shale oil wells. The average drilling depth and average ROP were 4402.6 m and 8.86 m/h, respectively, indicating that one-trip drilling was realized in the kilometric horizontal section of horizontal shale oil wells in the Jiyang Depression and thus the complex efficiency was lowered significantly. This study can provide technical support for the effective development of shale oil resources in the Jiyang Depression and a reference for best practices in the exploration and development of other shale oil blocks in China.
Study and Test of Horizontal Wells Subdivision Cutting Fracturing Technology of Shale Oil
LI Shanshan, SUN Hu, ZHANG Mian, CHI Xiaoming, LIU Huan
 doi: 10.11911/syztjs.2021080
[Abstract](22) [FullText HTML](13) [PDF 2094KB](8)
Aiming at shale oil reservoirs such as low brittleness index、undeveloped natural fractures and difficult to form complex fracture network, staged volume fracturing can not achieve maximum reservoir utilization. According to the principle of maximizing fracture-controlled reserves, On the basis of reservoir quality classification evaluation and heterogeneous geological model of shale oil horizontal section, Based on the spatial distribution of dessert and the comprehensive dessert index, the research on the design method of single-stage and single-cluster fracturing fracture layout by subdivision cutting is carried out, Optimized fracturing parameters, Formation of horizontal well subdivision cutting fracturing technology of shale oil. Field test of 10 shale oil horizontal wells in Changqing Oilfield using this technology, The field test results show that daily oil production of test wells is 35.9% higher than that of adjacent wells. It provides a new idea for shale oil reservoir reconstruction.
Practice and Development Suggestion of Volume Fracturing Technology for Shale Oil in Ordos Basin
ZHAO Zhenfeng, LI Kai, ZHAO Pengyun, TAO Liang
 doi: 10.11911/syztjs.2021075
[Abstract](31) [FullText HTML](8) [PDF 1807KB](12)
Volume fracturing technology can greatly increase the output of shale oil single well in Ordos Basin, but it is difficult to achieve economic and effective development under the condition of low oil price. For this reason, based on the field practice and laboratory test results of shale oil volume fracturing in Chang 7 member of Yanchang formation in Ordos Basin, the technical idea of volume fracturing is put forward by using big data analysis method, and the technical model of volume fracturing is formed. the volume fracturing parameter system is established. The results shown that the understanding of the imbibition mechanism of shale oil in the basin has gradually changed from the single effective displacement mechanism of conventional reservoirs to the compound mechanism of effective displacement and oil-water imbibition replacement. After years of field practice and related simulation research, the fracturing technology model of "large well cluster, long horizontal well, subdivision cutting, cluster perforation, soluble ball seat and variable viscosity slippery water" has been formed, and good field application results have been obtained. In order to deepen and enhance the volume fracturing technology and pursue the goal of higher productivity, some suggestions for further development of shale oil volume fracturing technology in the basin were put forward. it is suggested that we should continue to study the mechanism of increasing production by fracturing, optimize the key technical parameters and develop the visualization technology of volume fracturing. The research results can provide a scientific basis for the optimal design of volume fracturing of shale oil horizontal wells and can be used as a good reference for guiding similar reservoir production.
Drilling Technology of Fan Yeping 1 Shale Oil Horizontal Well in Shengli Oilfield
ZHAO Bo, CHEN Erding
 doi: 10.11911/syztjs.2021078
[Abstract](31) [FullText HTML](16) [PDF 1629KB](14)
There are abundant shale oil resources in the Dongying Sag, but the oil and gas geological conditions are complex. In order to investigate the oil and gas situation in the upper Shasichun member of Shahejie formation in the north of boxing sag, Dongying Sag, it is necessary to investigate the oil and gas content in the shale, the deployment of the shale oil horizontal well fan Ye Ping 1. According to the exploration purpose, the well was designed first, and then the drilling technical difficulties were analyzed based on the lithology of formation encountered in fanyeping 1 well, the well trajectory optimization technology, synthetic based drilling fluid technology and safe drilling technology have been studied and formed. The drilling operation of Fanyeping-1 well was successfully completed by using all the techniques studied. No downhole complications occurred during drilling, and the hole diameter enlargement rate was small. The successful application of well fanyeping 1 has accumulated experience for Shale oil drilling in Shengli Oil Field.
Research and Application of Large-segment Multi-cluster Fracturing Technology in Jimsar Shale Oil Horizontal Well
WANG Lei, SHENG ZhiMin, ZHAO ZhongXiang, SONG DaoHai, WANG LiFeng, WANG Gang
 doi: 10.11911/syztjs.2021091
[Abstract](8) [FullText HTML](6) [PDF 1684KB](4)
Reservoirs in Lucaogou Formation in Jimsar Sag have poor physical properties, strong heterogeneity, and poor crude oil fluidity. It is difficult to accurately rebuild superior reservoirs with horizontal wells. The effect of staged fracturing is limited, and the contradiction between high input and low output of fracturing is prominent. In view of the problems in the development of horizontal wells in Jimsar shale oil, the non-uniform limit flow-limiting hole arrangement technology is used to improve the distribution of fracturing fluid in each cluster in the section, and the temporary plugging of the fracture and the temporary plugging of the inner seal are used to increase the net pressure to form a complex fracture network, and optimize the fracturing construction parameters to promote the increase in the section. The cluster fractures are balanced, and finally a large-section multi-cluster fracturing technology suitable for horizontal wells in the Jimsar shale oil reservoir is formed. Field application results show that the implementation of large-scale multi-cluster fracturing and supporting technologies can effectively improve the degree of shale oil reservoir reconstruction and production effects, and provide strong support for the economic and effective development of shale oil.
Study on Nano Composite Cement Slurry System Suitable for Low Temperature Formation
WANG Sheng, CHEN Qiang, YUAN Xuewu, HUA Xu, CHEN Liyi
 doi: 10.11911/syztjs.2021009
[Abstract](31) [FullText HTML](18) [PDF 1304KB](17)
In order to solve the problems of borehole wall collapse and well leakage during drilling in low temperature formation, a new nano-composite cement-based grouting material system suitable for low-temperature formations has been developed. The effect of nano-Al2O3 on the performance and hydration process of low-temperature silicate-thioaluminate composite cement slurry was studied by combining macroscopic test and microscopic analysis. Through the "synergistic hydration" effect induced by mixing ordinary Portland cement with sulphoaluminate cement, together with nano-Al2O3, antifreeze agent (EG), water reducing agent (JS-1), early strength agent (TEOA), a new composite cement slurry (NAC) was developed, an integrated analysis of scanning electron microscopy, X-ray diffraction and hydration exotherm was used to observe and analyze the patterns of the low temperature hydration process of NAC. The experiment concluded, at a low temperature of –9 ℃, the nano-composite cement cement (NAC) had good initial fluidity, with a pumpable period of 57 min, and 24 h compressive strength of 6.9 MPa. Research shows that NAC has the effect of 'right angle thickening' and the performance is superior at low temperature, which can meet the performance requirements of borehole wall protection and plugging in low temperature formation drilling.
Large-scale Energy Storage Volume Fracturing Technology for Horizontal Wells of An83 Shale Oil Block
LI Kaikai, AN Ran, YUE Pandong, CHEN Shidong, YANG Kailan, WEI Wen
 doi: 10.11911/syztjs.2021026
[Abstract](50) [FullText HTML](13) [PDF 1681KB](12)
An 83 shale oil reservoir is located in Ordos Basin, because of factors such as tight reservoir physical properties, lack of effective energy supplementation, so the early measures to increase well production failed to achieve the expected effect. Considering the exploration of water injection and repeated fracturing tests in the early stage, on the basis of water injection to complement formation energy and upgraded tool, combining extreme clumps perforation, differentiation of reservoir reconstruction and multistage dynamic temporary plugging technology, the fracture complexity was constantly improved, at the same time, the soak time was optimized to make oil and water phase fully imbibition replacement, ultimately, the large-scale energy storage volume fracturing technology was invented. Field tests were carried out, the production of horizontal wells was significantly increased, with the highest daily oil production of measured wells reaching 7 times that of adjacent wells. After 10 months of production, the cumulative oil of single well reached 2 010 tons, the effect and economic benefit were significantly improved. Large-scale energy storage volume fracturing can both supplement the formation energy and effectively transform the reservoir formation, so it has some reference value for the development of other similar reservoirs.
Drilling Technique of Zhong Ping 1 well for Deep Shale Gas Horizontal Wells in the ordos basin
SHI Chongdong, WANG Wanqing, SHI Peiming, YANG Yong
 doi: 10.11911/syztjs.2021007
[Abstract](62) [FullText HTML](17) [PDF 1597KB](26)
In order to find out the potential of hydrocarbon generation and accumulation in the mud carbonate rocks of Wulalike Formation in the west of Ordos Basin, the exploration effect of unconventional resources will be improved in the area. Well Zhongping 1 is the first horizontal well of marine sedimentary shale gas deployed in Changqing Oilfield. The "double stage PDC + single bend screw" sidetracking technology was adopted to improve the sidetracking efficiency of large borehole; the "multi particle bridge plug + fiber cement" plugging technology was optimized, high-performance nano plugging high-performance water-based drilling fluid system, and the application of power drive orbit with personalized PDC bit in horizontal section. The successful exploration of zhongping1 well is estimated to be 11.65×104 m3/d, and the daily gas production is stable at (15–20)×104 m3, the successful test production of this well marks a major breakthrough in the exploration of the first horizontal well of marine shale gas in the north of China, it is of far-reaching significance to realize the orderly succession of resources.
Key drilling technology of the extended reach well in the South China Sea with ultra-high horizontal displacement to vertical depth ratio
ZHANG Qiang, QIN Shili, RAO Zhihua, TIAN Bo, ZUO Kun
 doi: 10.11911/syztjs.2021045
[Abstract](52) [FullText HTML](20) [PDF 1852KB](21)
An extended-reach well M with ultra-high horizontal displacement to vertical depth ratio up to 4.9 is designed to develop marginal oil reservoirs. During the drilling process, the well suffered from technical problems such as narrow pressure window, hole cleaning difficulties, and high casing-running friction resistance. A series of technologies and researches including well trajectory and well structure optimization, wellbore equivalent circulating density ECD control method and efficient casing running technology were successfully developed. The application of ϕ244.5 mm motor with high angle ensuring the shallow strata deflection; optimized well structure significantly improving the wellbore stability; the application of continuous circulation valve system and “cuttings bed” destroyers successfully eliminating the ECD change rate on bottomhole to less than 1.9%; the application of floating casing running technology and rotated liner running process technology ensuring the ϕ244.5 mm casing and ϕ177.8 mm liner run to the designed depth. The major breakthrough in drilling well M provides technical supports and valuable experience for the development of extended-reach wells in offshore oilfields.
Key Technology of Volumetric Fracturing in Giant~Thick Shale Oil Vertical Wells of Fengcheng Formation in Mahu Depression
HAO Lihua, GAN Renzhong, PAN Liyan, RUAN Dong, LIU Chenggang
 doi: 10.11911/syztjs.2021092
[Abstract](24) [FullText HTML](11) [PDF 3408KB](11)
The shale oil reservoir of the Fengcheng Formation in the Mahu depression is deeply buried, thick, oil~bearing overall, dense matrix, and rich in metal ions. Fracturing faces many challenges, include insufficient of vertical production, low fracture complexity, high sanding risk, and the incompatibility of HPC fracturing fluid. In order to fully release the exploration potential of shale oil in this area, by finely described the mechanical properties of the reservoir and the formation capacity of fracture network, the calculation model of the compressibility index was established, combined with the longitudinal expansion ability of artificial fractures, the perforation clusters and cluster spacing were optimized to form a vertical fine Layering method; based on the development of natural fractures, the volume fracturing process was optimized, the net pressure in the fracture was increased by the large displacement construction, the multi~scale filling of the combined particle size proppant, the slow~increasing pumping safety sanding was formed, and the large~scale transformation combined process and key parameters was formed; supporting the research and development of temperature~resistant and salt~resistant polymer fracturing fluids to comprehensively form key technologies for vertical well volumetric fracturing in deep and thick shale oil reservoirs in Mahu. The Fengcheng Formation shale oil reservoir of Well MY1 adopts this technology, the construction success rate is 100%, and gets the high~yield oil flow of 50 m3 per day after compaction. The development of oil benefits is of great significance.
Research on Production Optimization of Continental Shale Oil Well with Enhanced Stimulated Reservoir Volume Fracturing in Dongying Sag of Shengli Oilfield
WANG Zenglin, LU Mingjing, ZHANG Liaoyuan, LI Aishan, MENG Yong, ZHENG Bintao
 doi: 10.11911/syztjs.2021074
[Abstract](27) [FullText HTML](16) [PDF 2238KB](12)
To improve the whole-life oil production of continental shale oil well in Dongying Sag of Shengli Oilfield, the proper drainage system of wells with enhanced stimulated reservoir volume fracturing (ESRV) treatment is researched. Based on the complicated storage and seepage mechanisms of the shale oil reservoir, a mathematical model of the shale oil reservoir is established to characterize the two-phase seepage in dual medium in the whole life of fracturing-well resting-producing periods. Production variation with the different drainage systems (different well resting times and pressure drop rates in the flowing and pumping periods) is researched, and the proper production optimization method is discussed by numerical simulation. The optimized drainage system can be obtained based on the simulation results: proper well resting time after fracturing is about 60 d; optimized daily drop of wellhead pressure of flowing period is 0.06–0.10 MPa/d in the early-stage and then 0.02–0.04 MPa/d in the mid-stage, while in the late-stage, the best way is to release the pressure to 0 as soon as possible; slow pressure drop should be maintained in pumping period to keep sustainable production of the oil well, in case that there is not enough oil supplying from the formation matrix due to quick pressure drop. The researching results can provide some theoretical guidance for development optimization for continental shale oil in Dongying Sag of Shengli Oilfield, and meanwhile provide some references for fractured horizontal well production optimization in other shale oil reservoirs.
Short Circuit Test Method and Field Application of Short Light Liner in Deep and Ultra-Deep Wells
LIU Guoxiang, ZHAO Deli, LI Zhen, KONG Bo
 doi: 10.11911/syztjs.2021042
[Abstract](44) [FullText HTML](26) [PDF 1562KB](18)
In order to accurately test the short-circuit problem of short light liner in deep and ultra-deep wells, the test method of variable density slurry circulating pressure change curve is proposed, which based on the research and analysis of the conventional test method of liner short-circuit, and combined with the actual construction conditions. This paper analyzed the principle and control process of variable density cycle test, and studied the operational test program and key technical points. The circulation pressure of variable density slurry is highly sensitive to the change of downhole circulation channel, which is reflected in different curve changes on the pressure curve. By comparing the field measured pressure curve with the theoretical pressure curve, the short circuit of downhole string can be accurately judged. The field application results show that the test method has the advantages of strong anti-interference factors, high accuracy of test results, and simple field operation. It can carry out accurate and effective short circuit test on the liner string. The variable density slurry circulating pressure curve test method, as a short-circuit test method of downhole string, solves the problem of short-circuit test of short light liner in deep and ultra-deep wells, and has good promotion value.
Development situation and Countermeasures of oil and gas industry under the constraint of carbon neutralization
WANG Minsheng, YAO Yunfei
 doi: 10.11911/syztjs.2021070
[Abstract](80) [FullText HTML](56) [PDF 1832KB](32)
To cope with the climate changes, many countries have clearly put forward the carbon peak and carbon neutral schedule. Low carbon economy is an inevitable choice, and the energy structure will continue to turn to low carbon. Therefore, the proportion of fossil energy demand will decline significantly, and the development of oil and gas industry is facing severe challenges. For these reasons, this paper first analyzes the characteristics of low-carbon transformation of economy and energy under the constraint of carbon neutralization, and the impact of carbon neutralization on the oil and gas industry. Then it introduces the main measures taken by oil companies and oil service companies to cope with the carbon neutralization goal, including formulating green low-carbon development strategy, accelerating the development of low-carbon energy business, increasing the research and application of low-carbon technology, increasing investment in new energy business, and so on Finally, suggestions for the development of China's oil and gas industry are put forward, including promoting the upgrading of oil and gas industry, orderly promoting the transformation of low-carbon energy, accelerating the innovation of low-carbon technology, and accelerating the transformation and development of oil and gas industry. It can help to accelerate the coordinated development of new energy and conventional oil and gas business, and promote the green and low-carbon transformation of enterprises.
Research and Application of Oil-Based Drilling Fluid Technology for Strong Plugging in Changning Block
WANG Zhiyuan, HUANG Weian, FAN Yu, LI Xiaojie, WANG Xudong, HUANG Shengming
 doi: 10.11911/syztjs.2021039
[Abstract](27) [FullText HTML](9) [PDF 2530KB](7)
It is very important for horizontal drilling in Changning block to find out the reasons of wellbore instability in Longmaxi Formation and Wufeng Formation, and put forward the drilling fluid technical countermeasures to strengthen and stabilize wellbore. Based on X-ray diffraction, scanning electron microscope, shale swelling and rolling dispersion tests, the mechanism of wellbore instability in complex strata is revealed, and the cooperative wellbore stability method is put forward, which is "strengthening plugging micro pores, inhibiting filtrate invasion and retarding pressure transmission". Using sand bed filtration tester, high-temperature and high-pressure filtration simulator, microporous membrane and other experimental devices, the oil-based drilling fluid treatment agent in Changning block was researched and selected, and an enhanced plugging drilling fluid system suitable for Changning block was constructed. Its temperature resistance is 135 ℃, salt resistance is 10%, calcium resistance is 1%, poor soil resistance is 8%, the bearing capacity of 400 μm fracture is 5 MPa, and the filtration loss of 0.22 μm and 0.45 μm microporous membrane is both 0 mL. The plugging effect is outstanding, and its comprehensive performance is better than that of ordinary drilling fluid. The drilling fluid has been applied to more than 10 wells in Changning block, and there is no wellbore stability problem in the horizontal section of Longmaxi Formation and Wufeng Formation; Compared with the drilled wells using conventional drilling fluid technology in the same block, the hole diameter enlargement rate of complex formation is reduced by 10.82% on average, and the well construction period is shortened by 4.5 days on average. The research results show that the enhanced plugging oil-based drilling fluid technology has a good effect on solving the wellbore instability in Longmaxi Formation and Wufeng Formation of horizontal wells in Changning block.
The Key Drilling Technologies of Ultra-Shallow Horizontal Wells in Jihua-1 Fault Block Jilantai Oilfield
TAN Tianyu, QIU Aimin, TANG Jihua, LI Hao, XI Jia'nan, HUO Lifen
 doi: 10.11911/syztjs.2021038
[Abstract](35) [FullText HTML](18) [PDF 587KB](14)
For several intractable issues happened during the Horizontal Wells drilling process in Jihua-1 fault block, difficult to guarantee build-up ability since the soft feature of the Cretaceous formation, poor drillability and difficultly direction build up due to the high hardness of anisotropic metamorphic rock, extending horizontal section difficultly, difficult to drip in casing safely, low Rate of penetration (ROP) etc.. To treat these problems, a series of technical methods were carried out. This paper combined with the geologic features of this fault block, applying gneiss rock mechanics parameters to do numerical calculation for optimizing the casing program and well trajectory. Introduced personalized PDC Bits design and optimized the bottom hole assembly (BHA) and downhole tools. In addition, a series of assorted technologies has been set, such as environmental protection low solid drilling fluid, and floating scenario casing tripping in technique. According to the study and in-situ experiment, the technologies of Drilling&Completion wells in Ultra-shallow horizontal wells in Jihua-1 fault block Jilantai Oilfield have been formed. No any complex issue happened during the drilling process in 4 wells, which provided technical support for the subsequent development of this block.
Optimization Design and Numerical Analysis of Flow Channel Converter of LWD Tool
YAO Xiaojiang, LU Huatao, SHANG Jie, WANG Qinghua, LI Yang
 doi: 10.11911/syztjs.2021069
[Abstract](60) [FullText HTML](19) [PDF 1065KB](17)
Improper design of flow channel section of flow channel converter in LWD tool will not only cause local flow field turbulence in the flow channel of LWD tool, cause serious local erosion of the tool and shorten the life of the tool. It will also lead to high pressure loss of the tool and affect the applicability of the tool. Therefore, the CFD method is adopted to optimize the design of a certain type of LWD tool flow channel converter. The four design schemes before and after the optimization are simulated and compared in full three-dimensional, and the main factors affecting the flow field performance of flow channel converter are considered. It is the continuity of the expansion angle and the cross-sectional area of internal flow channel. The optimal design has a smaller expansion angle, a continuous cross-sectional area of internal flow channel, a smoother axial velocity drop, a minimum total pressure loss, and a more uniform flow velocity distribution in the flow field. Research shows that the expansion angle of flow channel converter and the discontinuity of the cross-sectional area of the internal flow channel are negatively correlated with the uniformity of the flow field distribution of flow channel converter, and positively correlated with the pressure loss. The test verification results show that the difference between theoretical value and experimental value of total pressure loss coefficient is not more than 0.076%, and the change trend is the same as the theoretical analysis result. The research results provide a theoretical basis for the design of flow channel converter.
Drilling Artificial Intelligence Technology Research Method and Practice
YANG Chuanshu, LI Changsheng, SUN Xudong, HUANG Liming, ZHANG Haolin
 doi: 10.11911/syztjs.2020136
[Abstract](100) [FullText HTML](50) [PDF 999KB](60)
The artificial intelligence (AI) has made remarkable breakthroughs in some sectors, but its application to drilling is still in the primary stage. In order to promote the application of artificial intelligence technology in the drilling field, based on a brief description of the research situation of artificial intelligence application in the drilling industry, a "three-wheel drive" methodology for the specific application of artificial intelligence technology to the drilling field is proposed, and the drilling field is suitable for development. Then, business application scenarios and artificial intelligence technology tools suitable for the research of artificial intelligence in drilling field were identified. Next, after putting forward a, method of evaluating and optimizing projects based on the methodology with examples, the research process of AI application to drilling was illustrated by the real-time diagnosis of complex downhole failures. Finally, the shortcomings were identified and suggestions in drilling engineering were given, so as to promote the development of artificial intelligence drilling technology.
Research and Application of High Temperature Drilling Fluid for Deep Wells Based on the Concept of Constant Rheology
SHU Yiyong, SUN Jun, ZENG Dong, XU Sixu, ZHOU Huaan, XI Yunfei
 doi: 10.11911/syztjs.2021037
[Abstract](52) [FullText HTML](27) [PDF 616KB](18)
the safety density window of drilling fluid in the deep formation of Yuemanxi block in Tarim Oilfield is narrow, and there are downhole complications such as lost circulation, well collapse, sticking and salt water immersion. The drilling fluid has technical problems such as high temperature thickening, poor resistance to CO32–/ HCO3– and poor quality soil pollution. A high temperature constant rheological drilling fluid system with new high temperature stabilizer (HTS220) and high temperature resistant polymer fluid loss reducer (APS220) as main agents was studied. The high temperature rheological properties of the system at different temperatures, different dosages of CO32– / HCO3– pollution and sodium bentonite pollution were evaluated. The results show that at 100 ℃ and 180 ℃, the plastic viscosity ratio is 1.3, the dynamic shear ratio is 1.5, the initial shear ratio is 1.7 and the final shear ratio is 1.2. The rheological properties of the system are constant. With the increase of temperature, the variation range of rheological parameters is significantly lower than that of other common drilling fluid systems. The resistance to CO32– / HCO3–compound pollution is 2%, and the resistance to sodium bentonite pollution is 10%. In the application process of Yuemanxi two wells, the rheological property of drilling fluid is stable, the borehole is smooth, the downhole complexity is reduced, and the application effect is good, which can meet the drilling requirements of this block.
Measurement of the Downhole Drill String Vibration Signal and Analysis of the Vibration Excitation Sources
CHEN Huijuan
 doi: 10.11911/syztjs.2021011
[Abstract](141) [FullText HTML](57) [PDF 2269KB](49)
To clearly identify the downhole drillstring vibrations and the vibration excitation sources in the drilling process, the vibration signals were measured during rotary drilling of an ultra-deep well by the Environmental Severity Measurement (ESM) storage system. According to the principle of measurement, the stick-slip and whirling vibrations of the drillstring were studied. On this basis, the frequency domain and time frequency of drillstring vibrations were analyzed by the fast Fourier transform and short-time Fourier transform. Then the main frequency causing drillstring vibrations was determined, and the vibration excitation sources were identified. The results demonstrated that during the stick-slip vibrations of the drillstring, the triaxial acceleration changed synchronously and periodically, with a period of 10 s. The main frequency component of 0.1 Hz. When the drill string experiences whirling vibrations, the measured three-axis accelerations showed disorderly and irregular fluctuations, and the main vibration frequency was the drill bit speed two times the frequency, 1 to 5 times the rotary table speed. Stick-slip and whirling vibrations were frequently encountered in the measured section of the well, and most of the interaction between the drill bit and the formation had to take into consideration the stabilizer friction, and additional friction between the stablizer and the Power-V system. The excitation sources that caused the whirling mainly consisted of the interaction between the drilling bit and the formation, the friction between the stabilizer or Power-V system and the borehole wall, etc.
The Optimization of Casing Thread Types for Horizontal Tight Oil Wells in the Mahu Oilfield, Xinjiang
SHU Bozhao, ZHAO Wenlong, WANG Hang, HUANG Yongzhi, ZHANG Zhi, ZHU Xiaohua
 doi: 10.11911/syztjs.2021041
[Abstract](94) [FullText HTML](38) [PDF 2219KB](41)
To tackle the fracture failure of casing thread joints when running casing in horizontal tight oil wells in the Mahu Oilfield, Xinjiang, we conducted numerical simulations of casing thread joints and full-scale experiments on casing to compare the connection strength and fatigue life of API-LC long round and TP-G2 special thread joints. In the simulations, the stress of TP-G2 special thread joints was significantly lower than that of the API-LC long round ones under the same tension or compression forces, and further, the fatigue life of TP-G2 special thread joints was about 6.9 times of that of API-LC long round thread joints under the same cyclic and alternating tensile-compressive load. According to our research, TP-G2 special thread joints can play a better role in meeting the technical demands when casing horizontal tight oil wells in the Mahu Oilfield, Xinjiang and in improving efficiency.
Research and Field Tests on the Technology of Coiled Tubing Fishing Sand-buried Restrictors
WANG Sifan, ZHANG Ankang, HU Dongfeng
 doi: 10.11911/syztjs.2021067
[Abstract](62) [FullText HTML](48) [PDF 900KB](27)
In order to solve the problem of gas wells shutdown caused by the failure of fishing sand-buried restrictors, the sand burial principle and identification method of restrictors in gas wells are introduced based on the structure principle of slip type restrictors. And the fishing complicated reasons of the sand-buried restrictors are analyzed combined with the previous conventional wire fishing operations, coiled tubing grinding-milling fishing operations, and pulling tubing string. The technical ideas and construction process of coiled tubing for sand flushing and fishing sand-buried restrictors are put forward. The corresponding sand flushing and fishing tool strings are recommended as well. It also theoretically analyzed the minimum sand flushing displacement corresponding to the coiled tubing and tubing size. In the field tests of 4 horizontal wells, the 88.9 mm sand-buried restrictors were successfully fished after sand flushing with the 100% success rate. And the average total time took less than 1.5 days. The research results show that the technology of coiled tubing for sand flushing and fishing sand-buried difficult restrictorsis feasible, efficient and has a high success rate, which has good value for field promotion and application.
Performance Evaluation and Field Application of Self - consolidation Plugging Agent
WANG Zaiming, XU Jing, ZHANG Yixing, SHENG Yuanyuan, XU Xiaofeng, LI Xiangying
 doi: 10.11911/syztjs.2021044
[Abstract](71) [FullText HTML](28) [PDF 798KB](31)
In order to solve the problem that conventional compound plugging agent is vulnerable to mud erosion and negative pressure damage to the plugging layer, resulting in low plugging success rate, the self-consolidation plugging leakage agent is studied. Using fluidized coating equipment to coat the outer surface of the plugging agent with a layer of epoxy adhesive that can be cemented at the underground temperature, thereby increasing the strength of the plugging layer formed by the plugging agent under the well. By adjusting the inlet air temperature of the fluidized coating machine 50 ~ 100 °C, the outlet air temperature 25 ~ 40 °C, the rate of the spray gun 0.5 ~ 2 L/h can complete the spray, coating, and drying. The experiment of in door high temperature plugging shows that the self-consolidation plugging leakage agent has good anti-mud disturbance and anti-negative pressure suction. By choosing the type of epoxy resin and adding the amount of accelerator, the consolidation time of self-cementing and plugging agent can be adjusted under the well, at 110 °C, the plugging agent has begun to solidify at 2 h, and the pressure at 15 h reaches 4.6 MPa. Scanning electron microscope photos of plugging layer showed that the coating layer softened and consolidated in the process of temperature rise, and the bonding between materials was tight after consolidation. Application in NPA and other well site shows that self-consolidation plugging leakage agent can greatly improve success rate of serious fracture loss.
Comprehensive Evaluation and Optimization of Working Fluids in Coaxial Borehole Heat Exchange Geothermal System
YU Chao, ZHANG Yiqun, SONG Xianzhi, WANG Gaosheng, HUANG Haochen
 doi: 10.11911/syztjs.2021066
[Abstract](49) [FullText HTML](31) [PDF 906KB](21)
As for Coaxial Borehole Heat Exchanger (CBHE) geothermal system, the influence of different working fluids on the heat extraction performance of the system is not yet clear, and a single factor cannot fully evaluate it. In this paper, a three-dimensional fluid flow and heat transfer numerical model of coaxial borehole heat exchange geothermal system was established using COMSOL, and was verified with field data. Then, four parameters, including outlet temperature, heating power, cyclic pressure loss and coefficient of performance (COP), were selected. And the weight coefficients of them was determined by the Analytic Hierarchy Process. Finally, based on the Fuzzy Comprehensive Evaluation method, a program was used to comprehensively evaluate the heat extraction performance of the nine working fluids. Based on the results of the comprehensive evaluation, the circulating masses were classified into three levels, with CO2 scoring the highest, indicating that CO2 has excellent overall heat extraction performance and is the optimal circulating mass. The study shows that the comprehensive evaluation model can comprehensively evaluate the heat extraction performance of the circulating masses, and the use of CO2 as the circulating mass can significantly improve the heat transfer efficiency of the CBHE geothermal system.
Research and Application of a ϕ273.1 mm Infinite Circulation Liner Hanger in the Yuanba Gas Field
GUO Zhaohui, LI Zhen
 doi: 10.11911/syztjs.2021004
[Abstract](63) [FullText HTML](40) [PDF 878KB](35)
Technical problems were encountered when cementing the ϕ273.1 mm liner in the Yuanba Gas Field, such as long open hole and liner sections and small annular gaps, which led to further difficulties in running the liner in place and measuring slurry displacement, as well as impeading the midway pump start-up. Considering geological conditions, borehole conditions, tool functions, etc., the infinite circulation liner hanger was adopted and integrated witha pressure balance mechanism and embedded slips, and subsequently combined with a supporting rubber plug system. Moreover, specific measures for running the liner were introduced. Implementing the approach in 7 wells of the Yuanba Gas Field eliminated the the midway circular resistance and allowed the crew to safely run casinginto the targeted area, with 100% liners arriving at the end of the hole. The compound signal of rubber plugs was evident, and slurry replacement was accurate, with the bump rate of 85%. The results confirmed the remarkable performance of the infinite circulation liner hanger when cementing the ϕ273.1 mm liner in the Yuanba Gas Field. This technique is effective in cementing large liners with a long open holes and thus worthy of popularizing for similar cases.
Research on Crude Oil Thickening Mechanism of Nitrogen Injection in Fractured Reservoir
LIU Zhongyun, LI Zhaomin, ZHAO Haiyang
 doi: 10.11911/syztjs.2021015
[Abstract](35) [FullText HTML](31) [PDF 888KB](16)
In order to clarify the thickening mechanism of carbonate reservoir by nitrogen injection and formulate corresponding countermeasures, so as to ensure the development of EOR technology by nitrogen injection, the study on the thickening mechanism by nitrogen injection in fracture-cavity reservoir was carried out. In this study, three high temperature and high pressure experiments were simulated, including the test and analysis of the influence of nitrogen injection and extraction on viscosity, the test and analysis of the influence of oxygen oxidation in nitrogen with different oxygen content on viscosity, and the test and analysis of the influence of crude oil mixing with water on viscosity. The experiment showed that the oxygen content in nitrogen was the main factors of higher viscosity, when the oxygen content was 1%, it only took more than 2 days to exhaust the oxygen, and the viscosity reached 18 000 mPa·s, which was 6 times of the initial viscosity, when the oxygen content was 5%, the viscosity continued to increase to 1 122 000 mPa·s in more than 7 days, which was 366 times of the initial viscosity. Emulsified water and nitrogen extraction have the same effect on viscosity, increasing the viscosity by 2–4 times. Therefore, the most effective method of preventing crude oil viscosity from increasing is increasing the purity of injected nitrogen.
Optimized and Fast Drilling Technologies for Horizontal Shale Oil Wells in the Cangdong Sag
LIU Tianen, ZHANG Haijun, YUAN Guangjie, LI Guotao, YIN Qiwu, CHEN Fei
 doi: 10.11911/syztjs.2020127
[Abstract](179) [FullText HTML](77) [PDF 2063KB](71)
During the drilling of horizontal shale oil wells in the Cangdong Sag, the low ROP (Rate of Penetration), high safety risk, and uncertain cementing quality impeded the efficient exploration and development of shale oil. To address these problems, investigations were implemented on the detailed prediction of formation leakage pressure and collapse pressure. They were then carried out the optimization of casing programs and borehole trajectories and the personalized design of PDC bits. Further, the matching technologies such as brine drilling fluid, rotary steering drilling, ductile cement slurry, and floating displacement cementing were integrated, forming an optimized and fast drilling technology for the horizontal shale oil wells in the Cangdong Sag. This technology was applied in 20 horizontal shale oil wells in the Cangdong Sag, and the cementing quality was improved by 30.4%. For the wells with a depth of more than 4 500.00 m, the average ROP increased by 20.2%, and the average drilling cycle was shortened by 30.6%. For wells with a depth of lower than 4 500.00 m, the average ROP increased by 82.9%, and the average drilling cycle was shortened by 49.9%. These results demonstrated that the proposed technology could meet the requirement for the optimized and fast drilling of horizontal shale oil wells in the Cangdong Sag, providing a technical means for the efficient exploration and development of horizontal shale oil wells and also a reference for the drilling technology optimization of unconventional oil and gas reservoirs in the oilfields of China.
Research on the Whole Process of Slick Water Fracturing Technology of Continental Shale oOil in Dagang Oilfield
TIAN Fuchun, LIU Xuewei, ZHANG Shengchuan, ZHANG Gaofeng, SHAO Lifei, CHEN Ziwei
 doi: 10.11911/syztjs.2021021
[Abstract](192) [FullText HTML](64) [PDF 2019KB](46)
In order to improve the complexity of shale oil fracture and shale oil production, the research and development of new fracturing fluid system, proppant optimization and sanding process optimization were carried out. The research results show that the viscosity of the hydraulic fracturing fluid can be changed by changing the concentration of polymer drag reducer, and the sand carrying performance of the water can be improved. The 70/140 mesh quartz sand and 40/70 mesh mm ceramsite proppant are optimized to form the continuous sand adding process of the water. The pilot test has been carried out successfully. The maximum sand ratio of continuous sand addition is 22%, and the average sand ratio is 8.3%. Under the same liquid volume, the sand addition is twice as much as that before the study, which increases the conductivity of shale oil fracture and improves the degree of reservoir reconstruction, and has a good application prospect.
2021, 49(3): 0-0.  
[Abstract](72) [PDF 14799KB](67)
2021, (3): 1-2.  
[Abstract](79) [PDF 380KB](56)
Expert Viewpoint
Achievements and Developing Suggestions of Sinopec’s Drilling Technologies in Arctic Sea
LU Baoping, HOU Xutian, KE Ke
2021, 49(3): 1-10.   doi: 10.11911/syztjs.2021046
[Abstract](132) [FullText HTML](72) [PDF 2422KB](52)
The Arctic area is rich in oil and gas resources. However, its geological and environmental factors such as low temperature, shallow hazards, permafrost and extreme temperature change in wellbore bring many challenges to drilling operation. For this reason, during the "Thirteenth Five-Year Plan" period, Sinopec took safety, environmental protection and efficient drilling as its overall goals and focused on solving the problem of "cold" adaptability of drilling equipments and tools, drilling technologies and measures, wellbore working fluids. Research was performed on key technologies regarding drilling hazard assessment and control, environmental protection, key drilling equipments and tools, drilling techniques, wellbore working fluids, etc. Impressive progresses were made in the quantitative risk assessment method for hazards to shallow gas and gas hydrate formations, the orbital drilling rigs and tools utilized at −50 °C, stability evaluation and borehole stability control in permafrost, and engineering technologies related to drilling fluid and cement slurry under low temperature conditions. As a result, the key technology system of drilling in the Arctic sea was preliminarily developed. As the Arctic oil and gas development enters higher latitudes and thicker permafrost regions on land, and the oceans will advance to deeper waters, perennial ice or thicker ice floes, drilling in Arctic sea will face greater challenges and requires further progress. Therefore, it is necessary to build a complete drilling and completion technology system in the Arctic sea by improving the theories and methods and developing new key equipments and tools. With the system, the demands of efficient exploration and development of oil and gas reservoirs in the Arctic region can be realized, thereby enhancing the economic benefits and core competitiveness of China’s oil companies in international cooperation projects of oil and gas development in this area.
The Polar Cold Sea
Prediction Model and Distribution Law Study of Temperature and Pressure of the Wellbore in drilling in Arctic Region
YU Yi, WANG Xuerui, KE Ke, WANG Di, YU Xin, GAO Yonghai
2021, 49(3): 11-20.   doi: 10.11911/syztjs.2021047
[Abstract](119) [FullText HTML](57) [PDF 2921KB](41)
The low temperature condition of permafrost in Arctic region affects the rheology of drilling fluids and the distribution of temperature and pressure in the wellbore during drilling. In order to understand the influence law of permafrost in Arctic region on the temperature and pressure distribution in wellbore and provide a basis for the design and construction for drilling in Arctic region, a model to predict the wellbore temperature and pressure of drilling in Arctic region was built. It was based on the analysis of the influence of low temperatures on the rheology of water-based and oil-based drilling fluids, considering the coupling between permafrost and wellbore. By comparing the measured and test results, it was verified that the prediction accuracy of the proposed model met the requirements of drilling in Arctic region. The model was used to simulate the temperature and pressure distribution in a wellbore in Arctic region under the conditions of no circulation or pump function. The results showed that the drilling fluids absorbed the heat of the high-temperature formation and returned to the annulus transferring the heat to the permafrost in shallow part of the wellbore during the circulation. This process thawed the permafrost near the wellbore and the wellbore temperature was lowered due to the heat consumed by thawing. The circulating friction in annulus increases with the increase of circulation time. The longer the pump shutdown lasts, the closer the temperature of drilling fluid to the formation temperature in the wellbore. The larger the annular circulation pressure loss, and the higher the pump pressure. The research results can provide a basis and guidance for design and construction of drilling in Arctic region.
Performance Test and Numerical Simulation Research on Vacuum Insulated Casings for Permafrost Protection
ZHOU Xiaohui, SU Yinao, NIU Chengcheng, CHENG Yuanfang, WEI Jia
2021, 49(3): 21-26.   doi: 10.11911/syztjs.2021050
[Abstract](84) [FullText HTML](48) [PDF 2212KB](29)
Because permafrost settles as it thaws, there is a risk that the wellhead will sink while drilling, and therefore, vacuum insulated casings were introduced to protect the permafrost, and their thermal insulation performance was analyzed through experiments and numerical simulations. The field test results showed that the vacuum insulated casings could limit both the radial and the axial heat transfer on the surface simultaneously, which restricts the range and magnitude of temperature increase on the casing surface. Because the vacuum insulated casings have much lower apparent thermal conductivity than that of traditional casings, their thermal insulation performance can be maintained at various ambient temperatures and drilling fluid temperatures. In addition, decreasing the vacuum degree can improve their thermal insulation performance and strengthen their protection of the permafrost. The numerical simulation results indicated that the vacuum insulated casings could greatly reduce the permafrost thaw zone and lower the possibility of settling and wellhead sinking due to permafrost thaw. Furthermore, the following measures were adopted to enhance the thermal insulation performance of the vacuum insulated casings, including vacuum degree reduction, insulated casings length increase in the casing assembly, and insulation foam wrapping at the coupling. The research results have verified the effectiveness and stability of vacuum insulated casings in protecting the permafrost, so as to guide the development of oil and gas resources in the Arctic region.
Triaxial Mechanical Tests and Multiple Regression Strength Analysis of Simalted Frozen Soil Sample from Mohe
NIU Chengcheng, HOU Xutian, LI Yang
2021, 49(3): 27-34.   doi: 10.11911/syztjs.2021049
[Abstract](66) [FullText HTML](35) [PDF 2059KB](30)
Improper drilling schemes may cause engineering problems such as wellbore collapse and wellhead subsidence during the drilling of permafrost. The research on mechanical evolution of deep frozen soil paves the way for construction design. In this paper, soil samples at different depths were remolded with the frozen soil from Mohe, and triaxial mechanical tests were carried out under different confining pressures and temperatures to analyze the characteristics of stress–strain curves of frozen soil under different conditions. The strength of frozen soil was statistically studied by multiple regression analysis, and the strength criterion for it was further established. The research results showed that the stress–strain curves of the frozen soil samples presented nonlinear deformation behavior on the whole. In its frozen state, soil strength was controlled mainly by temperature and confining pressure while it was dominated by confining pressure and soil depth in its non-frozen state. In addition, frozen soil strength was composed of the strength of soil skeleton and the cementing strength of ice in pores. The strength of soil skeleton satisfies the Mohr-Coulomb criteria, and the cohesion and internal friction angle increases with soil depth. The cementing strength of ice in pores grows with the decline of ambient temperature, and increases and then decreases as the confining pressure increases. On this basis, the strength criterion for Mohe frozen soil was established, and the verification results proved that it can well characterize the strength distribution of Mohe frozen soil in the melt and frozen state.
Mechanical Properties Test and Strength Design of Drill String Materials in Low-Temperature Environments
WANG Yanbin, ZHANG Hui, GAO Deli, KE Ke, LIU Wenhong
2021, 49(3): 35-41.   doi: 10.11911/syztjs.2021051
[Abstract](74) [FullText HTML](32) [PDF 3147KB](35)
Strength checking and design of drill strings at low temperature are crucial to solving the technical problems of drill string in low-temperature environments such as the Arctic region. In this paper, tests were carried out at both low and normal temperatures on drill string materials G105 and S135, and their temperature-dependent parameters including tensile strength, yield strength, and impact performance,etc. were obtained. On the basis of these results, the strength design method of drill strings in low-temperature environments was proposed. The results show that both tensile and yield strength of G105 and S135 increase as the temperature decreases while the cross section reduction rate remains unchanged. In low-temperature environments, it is important to note that to ensure the safety of the drill strings, their strength design should be controlled by both stress and strain, instead of only by stress in normal temperature environments. Yield strength of drill string materials should be determined according to the strength characteristics of the materials in the wide-temperature range. The results show that this study has directive significance to guarantee the engineering design of drill strings and their safety in low-temperature environments.
Research of the Influencing Factors on Thermal Insulation Effect of Casing with Parasitic Pipes and Central Tubing
BAO Hongzhi, SUN Yuanwei, ZOU Deyi, NIU Chengcheng
2021, 49(3): 42-47.   doi: 10.11911/syztjs.2021048
[Abstract](75) [FullText HTML](30) [PDF 2106KB](24)
In the process of drilling in permafrost, the frozen soil is susceptible to melt under the influence of drilling fluid. To solve this problem, casing with parasitic pipes and central tubing was introduced to insulate the pipe from the permafrost. Then, a set of test system for the thermal insulation of casing with parasitic pipes and central tubing was designed to analyze its performance and influencing factors. The experiment reveals that the central part of the casing can effectively suppress heat transfer in the radial and axial direction and keep the outer wall at a low temperature. However, thermal insulation of the couplings on both sides are poor, which raise the outer wall temperature, resulting in a U-shape distribution of it. In addition, the sensitivity analysis and single-factor fitting of environmental and operational parameters indicate that the temperature rise from the environment and fluids will increase the outer wall temperature linearly, and the increase of drilling fluid displacement will reduce the outer wall temperature following a logarithmic relationship. From the coefficient of the multivariate fitting equation, it is clear that the most influential factor on outer casing wall temperature is the environmental temperature followed by cold fluid and hot fluid temperature. The research results show that using casing with parasitic pipes and central tubing to protect the permafrost is very feasible, and engineering technical measures such as lengthening the intermediate casing section, improving the coupling structure, maintaining low temperature and displacement of cold fluid can significantly improve the protective effect.
Drilling & Completion
Drilling Technology for Adjustment Wells of the Jiaoshiba Block in the Fuling Shale Gas Field
FAN Hongkang, LIU Jinge, ZANG Yanbin, ZHOU Xianhai, AI Jun, SONG Zheng
2021, 49(3): 48-54.   doi: 10.11911/syztjs.2020122
[Abstract](174) [FullText HTML](78) [PDF 1838KB](77)
With the Jiaoshiba Block in the Fuling Shale Gas Field entering into the development and adjustment period, the recoverable reserves of single well are reduced. To develop the field economically, it is necessary to shorten the drilling cycle and reduce the drilling cost. Therefore, with the optimum design of drilling, drilling of ultra-long horizontal sections, increasing rate of penetration by optimization in drilling parameters, a “one-trip drilling” technique based on equal-life idea, integration of drilling, reaming and flushing in well completion, and long-term sealing technology in cementing, the drilling technology for adjustment wells of Jiaoshiba Block of the Fuling Shale Gas Field was formed. Field application results showed that the average length of horizontal sections in adjustment wells was 2 096 m, 37.8% longer than that in drilling the first phase drilling there. The average penetration rate reached 9.49 m/h, 26.2% higher than that in the first phase drilling and the drilling cycle was 62.27 d, which was 26.0% shorter than in the past. The percentage of wells with annular pressure lowered from 70.0% to 4.6%. The results show that the proposed key drilling technology could meet the technical needs of adjustment wells of Jiaoshiba Block of the Fuling Shale Gas Field, and provide supports for a stable production and more effective development of the Fuling Shale Gas Field.
Research and Field Test of Electrically Controlled Sidewall Deep Penetrating Perforating Technology
LIU Pingquan, LI Leibing, SHI Yucen, HAN Long
2021, 49(3): 55-61.   doi: 10.11911/syztjs.2021055
[Abstract](70) [FullText HTML](39) [PDF 2056KB](24)
Traditional explosive perforation is subject to a short penetration distance and a compaction effect. Although the existing hydraulic perforating technology has remedied the deficiencies, it needs to cooperate with oil tubing or coiled tubing, with a long operation period and a high cost. Also, it is difficult to monitor the construction process directly and accurately only with surface pump pressure signals. With regard to this problem, research was performed on electrically controlled sidewall deep penetrating perforating technology (ECSDPPT). DC motors were selected to replace high-pressure water pumps as the energy source. Perforating tools were suspended by electric cables for transmission instead of oil tubing or coiled tubing, and the cables also transmitted electrical energy and delivered commands to control perforating operations. A real-time monitoring system was developed to monitor the drilling process into formations timely and accurately. As a result, an electrically controlled sidewall deep penetrating perforating system was built. Ground and field tests prove that the ECSDPPT enables the drilling into formations by over 2.00 m, forming a borehole with a diameter of 20.0–30.0 mm. The monitoring system can accurately calculate the actual perforating length in time by identifying and recording the electric pulse signals from a downhole Hall sensor during formation drilling. The research results demonstrate that the ECSDPPT relying on cable transmission is fast, efficient and low-cost. It overcomes the shortcomings of conventional explosive perforation, providing a new method for connecting and reforming near wellbore formations. In addition, the monitoring system can record the drilling length and other parameters in real time during construction, effectively solving the failure of the existing hydraulic perforating technology in monitoring the working process.
Effect of Irregular Wellbores on Well Deviation in Air Drilling Through Thick Conglomerate Formations
LOU Erbiao, ZHOU Bo, LIU Hongtao, CHEN Feng, WANG Wenchang, XUE Yanpeng
2021, 49(3): 62-66.   doi: 10.11911/syztjs.2021003
[Abstract](123) [FullText HTML](32) [PDF 1988KB](40)
Proneness to well deviation and difficulty in casing running are two bottlenecks to be solved urgently in air drilling through the thick conglomerate formation. Field test data revealed that well deviation control was still challenging even air hammer drilling with a marked control effect on deviation was adopted, and wellbore regularity was poor. This phenomenon is difficult to explain with present theories of deviation control. Existing bottom hole assembly (BHA) force models do not consider the irregularity of the wellbore, and assume that the wellbore is smooth and regular. In this paper, the mechanical model of interaction between the irregular wellbore and BHA was built with finite element method on the basis of field data, and the influence of wellbore irregularity on the mechanical characteristics of BHA was analyzed. The model results demonstrate that the irregular wellbore is easy to form additional fulcrum and shorten the swing distance of pendulum BHA, thus greatly reducing deviation-reducing force. It may even convert the lateral force on the drill bit into a deviation-increasing force, resulting in well deviation control failure. It is confirmed by case analysis that the wellbore drilled by the pre-bent pendulum BHA is regular in air drilling through the thick conglomerate formation, with effective well deviation control and smooth running of casing. Field data indirectly supports the significant impact of wellbore irregularity on well deviation, which should be considered in the BHA mechanical analysis.
Study and Application of Wellbore Temperature Field Characteristics in the Ultra-Deep Slim-Hole Wells in the Shunbei No.1 Area
SU Xiong, YANG Minghe, CHEN Weifeng, ZHANG Jun
2021, 49(3): 67-74.   doi: 10.11911/syztjs.2021006
[Abstract](183) [FullText HTML](43) [PDF 2571KB](67)
The ultra-deep slim-hole wells in the Shunbei No.1 Area have high wellbore temperatures. In some wells, the temperatures even exceed the temperature resistance of the existing domestic measuring instruments, which often leads to probe burnout and no signal input to the instruments. To solve this problem, a mathematical model was established for transient wellbore temperature fields, which analyzed the field profiles at different parameters, and introduced the concept of “well depth at critical temperature” (WDCT). On this basis, in order to reduce the bottomhole circulating temperature and move the WDCT down to the bottom, the sensitivity of seven parameters were analyzed, including rheology, thermal property, displacement, and inlet temperature of drilling fluid, and the thermal property of the drill string. Then the physical parameters that could significantly influence the wellbore temperature field were obtained. It is found by analysis that WDCT could be divided into true, transitional, and equivalent categories according to the variation curves of wellbore temperature. The wellbore temperature field was sensitive to the thermal conductivity of the drill string, the specific heat capacity of drilling fluid, and the thermal conductivity of drilling fluid in a descending order, which corresponded to the equivalent WDCT. The results showed that changing the thermal properties of drilling fluid or reducing the thermal conductivity of the drill string could effectively lower the bottomhole circulating temperature in the Shunbei No.1 Area.
Research on Electromagnetic Detection and Positioning Methods and Tools for Relief Wells
HAO Xining, WANG Yu, DANG Bo, LI Fengfei, XU Liangbin, LIU Zhengli
2021, 49(3): 75-80.   doi: 10.11911/syztjs.2021005
[Abstract](109) [FullText HTML](38) [PDF 1967KB](44)
In order to connect relief wells with blowout wells and improve the accuracy of the target points, it is necessary to determine the borehole position of the blowout well with detection and positioning tools. However, there is currently a lack of relevant mature technology in China. In order to solve this problem, a transient electromagnetic relief well detection and positioning method is proposed in this paper based on symmetrical excitation. A calculation model for the detection distance and azimuth was derived from Maxwell’s equations, upon which a prototype of a relief-well detection and positioning tool was developed, and then tested in downhole condition. The test result showed that the maximum detection distance of this tool reached 24.0 m, with the errors of distance and azimuth less than 10% and 5°, respectively. The research indicated that the tool could accurately locate the borehole of the blowout wells and directly connect the relief wells with the blowout wells, which laid a foundation for the relief well detection, positioning and connection technology with independent intellectual property rights in China.
Ultra-Short Liner Cementing Technology for Highly Deviated Wells in the Chenghai Oilfield
HU Jinjun, ZHANG Lili, ZHANG Yao, MENG Qingxiang, HUANG Zhigang
2021, 49(3): 81-86.   doi: 10.11911/syztjs.2020132
[Abstract](90) [FullText HTML](39) [PDF 1682KB](34)
In the Chenghai Oilfield’s highly deviated wells, the intermediate casing cannot be run to the correct depth, so that the water layers cannot be isolated. During the remedial cementing with ultra-short liners, there are such problems in the highly deviated segments as low hang weight, difficulty in releasing and its identification, an active water layer susceptible to channeling, a poor centralization grade of the liner, and low displacement efficiency. For that reason, the ultra-short liner cementing technology for highly deviated wells was investigated. A hold-down sub installed under the parker-type liner hanger could increase the hang weight of the liner. The expanding cement slurry system was used to prevent the formation water from channeling. The centralizer position was optimized with PVI to raise the centralization grade of liner, and the structure and rheological properties of cementing slurry column were optimized to improve displacement efficiency. The ultra-short liner cementing technology for highly deviated wells was then developed. The technology was applied in two highly deviated wells in Chenghai Oilfield, with a high downward force of the hold-down sub, successful liner releasing and evident identification of it, and well isolated oil-water layers. In the later production rounds, stable and high oil flow was obtained. The research demonstrates that the ultra-short liner cementing technology for highly deviated wells solves the problem of ultra-short liner cementing for highly deviated wells in the Chenghai Oilfield, and also provides a technical reference for cementing in other similar complex situations.
Rock Breaking Process and Efficiency Analysis of Conical Cutting Teeth under Rotary and Torsional Impact
HU Sicheng, GUAN Zhichuan, LU Baoping, LIANG Deyang, HU Huaigang, YAN Yan, TAO Xinghua
2021, 49(3): 87-93.   doi: 10.11911/syztjs.2021035
[Abstract](130) [FullText HTML](55) [PDF 2352KB](55)
In order to gain a better understanding of the rock-breaking process and efficiency of conical cutting teeth under rotary and torsional impact loads, numerical simulation and experimental data verification were conducted to study the rock’s internal stress changes, damage characteristics, breaking volume, depth and rock breaking specific work by the two methods at different impact amplitudes and frequencies. The numerical simulation and analysis results showed that both the rock-breaking processes of conical cutters under rotary impact and torsional impact could be divided into four stages: cutter intruding into rock, damage through crack initiation, damage through crack propagation, and rock cuttings avalanche. The tensile stress is the main reason for the cracks from the inside to the surface of rock, and the internal damage and micro-cracks appear mainly due to compressive shear stress. With the increase of impact amplitude and impact frequency, the broken volume of rock will increase in both the two ways. When the impact amplitude and frequency are increased to certain values, the increase of rock-breaking volume tends to be mild, and the maximum rock-breaking volume under rotary impact is higher than that under torsional impact. Among the three rock breaking methods - conventional cutting, rotary impact and torsional impact - the rock breaking specific work of conventional cutting is the greatest, and the rock breaking specific work under the conditions of different impact amplitudes and frequency of torsional impact is generally lower than that of rotary impact.
Development and Field Application of a Coalbed Methane Coring Tool with Pressure Maintenance, Thermal Insulation, and Shape Preservation Capabilities
WANG Xigui, ZOU Deyong, YANG Liwen, GAO Wei, SUN Shaoliang, SU Yang
2021, 49(3): 94-99.   doi: 10.11911/syztjs.2021061
[Abstract](70) [FullText HTML](25) [PDF 4369KB](23)
In the process of lifting the coalbed methane (CBM) cores from the subsurface to ground, free gas escapes, adsorbed gas is partially desorbed and pore-permeability test data is distorted, seriously hampering the establishment of the CBM development plan. Therefore, a CBM coring tool with pressure maintenance, thermal insulation and shape preservation capabilities was developed. By designing an arc closed ball-valve, the failure in the pressure-maintenance seal was overcome by using a fully sealed ball-valve chamber that can withstand a pressure of 60 MPa. Using rubber tubes to hold cores and silica aeroge for thermal insulation, a composite coring inner barrel with thermal insulation function was designed, which allowed the coring tool to achieve the advantages of both pressure confinement and thermal insulation.The surface-set and impregnated composite diamond coring bit was optimized, thereby improving the coring bit footage. The CBM coring tool was applied to Well G-X20 for three times, obtaining a cumulative footage of 9.60 m, with a coring recovery rate of 94.48%, and a pressure maintenance rate up to 80%. The results showed that the proposed coring tool for CBM was very effective in pressure maintenance and gas preservation. Combined with sophisticated field construction technology, the coring tool can provide technical support for fine exploration and development of unconventional oil and gas resources such as coalbed methane and shale gas.
Design and Optimization of the Crawling Mechanism of Rotary Sidewall Coring Device in Shale Gas Wells
ZHU Weibing, ZHANG Chaojie, PANG Qingsong
2021, 49(3): 100-104.   doi: 10.11911/syztjs.2021043
[Abstract](95) [FullText HTML](40) [PDF 1741KB](33)
With regard to the problem that the rotary sidewall coring device of shale gas wells cannot be lowered to the coring position with its own weight, the operating requirements of the coring device were analyzed, and the resistance to the coring device in the horizontal wells was determined. Then, a new crawling mechanism transmitted by planetary and bevel gears was designed for rotary sidewall coring device. The functional relationships of the positive pressure of the crawling wheel and the extension speed of the supporting arm with each parameter were established. With the extension speed and push-the-bit force of the supporting arm as the multi-objective optimization function, the order of priority of the influencing factors such as the length, rotation angle, and eccentricity of the crawling arm and the length of the supporting arm was determined through the orthogonal tests. Furthermore, the physical dimensions of the crawling arm and supporting arm were optimized. The analysis results demonstrated that the rotation angle of the crawling arm had the greatest influence on the extension speed and push-the-bit force of the supporting arm. When the rotation angle, length, and eccentricity of the crawling arm and the length of the supporting arm were 45°, 150 mm, 8 mm, and 140 mm, respectively, the extension speed and push-the-bit force of the crawling arm were optimal. The optimization of the lengths of the crawling and supporting arms facilitated the decline in the push-the-bit force needed by the supporting arm and the increase in the extension speed of the supporting arm. The crawling mechanism of the rotary sidewall coring device for shale gas wells provides a new driving method for the sidewall coring device.
Oil & Gas Exploitation
Experimental Study on Silt Distribution Law at the Front end of Fractures in Volume Fracturing
ZHANG Yanjun, GE Hongkui, XU Tianlu, HUANG Wenqiang, ZENG Hui, CHEN Hao
2021, 49(3): 105-110.   doi: 10.11911/syztjs.2021065
[Abstract](61) [FullText HTML](38) [PDF 2058KB](37)
The role of silt in volume fracturing of tight reservoirs is not yet clear, and so it is with its distribution law at the front end of the fracture. For this reason, a dynamic fluid loss analysis device was used to establish a simulation test method for the distribution of silt sand at the front end of volume fracturing fractures (hereinafter referred as “volume fractures”), and the distribution law and influencing factors of silt were studied on the basis of fracture surface morphology description. It is found by experiments that the sand-carrying fluid was gradually lost in the volume fractures, and the distribution of silt retained at the fracture front end was largely distinct after the fluid loss reached equilibrium. Meanwhile, the pressure in the fractures was gradually elevated and then became stable as the fluid loss continued. The distribution of silt at the front end of fractures can be reasonably characterized by the maximum transport distance and stable pressure. The maximum transport distance increases with widening aperture of the fracture front end, lowering roughness of fracture surfaces, and increasing fracturing fluid viscosity. Small particle size of silt also increases the maximum transport distance. In addition, the stable pressure in the fractures increases as the aperture of fracture front end decreases, the roughness of fracture surfaces increases, the fracturing fluid viscosity increases, and the particle size of silt decreases. The results demonstrate the addition of silt during fracturing can raise the pressure in fractures after plugging their front ends and restrain the fractures from growing too fast in a certain direction, thereby increasing the complexity of the fracture network.
A Pseudo-Steady-State Productivity Prediction Method for Fractured Carbonate Gas Wells Considering Stress-Sensitivity Effects
LI Jiang, CHEN Xianchao, GAO Ping, SHU Chenglong
2021, 49(3): 111-116.   doi: 10.11911/syztjs.2021032
[Abstract](166) [FullText HTML](62) [PDF 1934KB](48)
To accurately evaluate the impact of the non-Darcy and stress-sensitivity effects on the productivity of fractured carbonate gas wells, a new dual-media binomial productivity model for radial compound reservoirs was established. The model is divided into an inner zone and an outer zone, in which the inner zone is designed to simulate the production process of gas wells after fracturing treatment. The new model is used to calculate the productivity of a well in a fractured carbonate gas reservoir in the Sichuan Basin. The calculation results showed that the model can predict the absolute open flow of gas wells in fractured carbonate reservoirs more reasonably and has achieved better field application results than the one-point method. According to the parameter sensitivity analysis, stress sensitivity factors mainly influence the late production stage of gas wells, and the formation coefficient plays an important role in influencing the absolute open flow, which demonstrates that formations with higher permeability and thickness are more favorable to the development of gas wells. The productivity prediction model of fractured carbonate gas reservoirs, which comprehensively considers non-Darcy and stress-sensitive effects, can provide a theoretical basis for the efficient development and reasonable production allocation of gas reservoirs.
Research on Visualization Experiment of the Gas Conduction and Water Blocking Effects of Coated Proppants
TAN Xiaohua, DING Lei, XU Weichong, QU Shuang, WEN Zhonglin
2021, 49(3): 117-123.   doi: 10.11911/syztjs.2021064
[Abstract](95) [FullText HTML](24) [PDF 2012KB](32)
To evaluate the effect of gas conduction and water blocking effects of coated proppants and provide the basis for achieving water control and stable production with coated proppant in low-permeability water flooding gas reservoirs, a coated proppant was developed for fracturing the water-invaded low-permeability gas wells with a spraying process, and water drop test was conducted to assess the hydrophobicity of the coated proppant. Relative permeability test of sand-filled pipes was carried out to analyze the rule for permeability of gas-water phase with the coated proppant and conventional quartz sand. To study the migration directions and laws of gas and water in the conventional quartz sand zone and the coated proppant zone during displacement, a seepage model was built by simulating the seepage channel, and a gas reservoir water flooding visualization experiment was conducted. The relative permeability test showed that the coated proppant could improve the relative permeability of the gas phase and inhibit the flow of the water phase. Through the visual water drive gas experiment, it is found that the coated proppant has the effect of "hydrophobic gas conduction". Compared with the simulated well in the conventional quartz sand zone in the model, the gas production of the simulated well in the coated proppant zone increased while its water production decreased. After re-fracturing with the coated proppant in the Well X21 of TN gas field, the gas production returned to normal and the water production plummeted, realizing the secondary production. The research results demonstrate that the coated proppant possesses a good gas conduction and water blocking effect, and can provide technical support for water control and stable production of low-permeability water drive gas reservoirs.
Research on the Planar Equilibrium Displacement Based on Maximum Water Injection Efficiency
CHEN Cunliang, MA Kuiqian, WANG Xiang, YUE Honglin, WU Xiaohui
2021, 49(3): 124-128.   doi: 10.11911/syztjs.2021028
[Abstract](75) [FullText HTML](45) [PDF 1630KB](46)
The existing planar equilibrium displacement evaluation method does not quantitatively consider the heterogeneity of the reservoir. For that reason, a new equation describing the relationship between water injection efficiency and cumulative oil production was built based on the dynamic displacement equation between injection and production wells with consideration of reservoir heterogeneity. The goal was to maximize water injection efficiency. The characteristic conditions of planar equilibrium displacement were obtained by derivation, on which the adjustment method for the injection–production structure of planar equilibrium displacement was developed. It is considered that the characteristic condition of equilibrium displacement in homogeneous reservoirs was that the ratios of injection volume to pore volume in all injection–production directions were the same; while that of equilibrium displacement in heterogeneous reservoirs was that the mentioned ratios in all injection–production directions were in a linear difference relationship. After adjusting the injection–production structure in the offshore BZ Oilfield by the planar equilibrium displacement method, the daily oil production increased by 155 m3, indicating the largely improved development effect. The results demonstrate that the planar equilibrium displacement method based on maximum water injection efficiency can be used guide the adjustment of the reservoir planar injection-production structure.
Research Progress and Development Suggestion of Stratified Acidizing Strings in Water Injection Wells of Shengli Oilfield
LI Yongkang, JIA Yiyong, ZHANG Guangzhong, WANG Hongwan, CUI Yuhai
2021, 49(3): 129-134.   doi: 10.11911/syztjs.2021030
[Abstract](106) [FullText HTML](69) [PDF 4150KB](43)
Stratified acidification is an important technique to solve the problem of the heterogeneity along the borehole and the blockage in the injection wells in Shengli Oilfield, which can be implemented by means of stratified acidizing strings. The technical requirements for this technique were analyzed and its current research situation was summarized with the field practice of Shengli Oilfield. According to the analysis, the existing basic strings, namely the K344, Y211/Y221, and Y341 could meet the requirements of the stratified acidizing of common injection wells in integrated, fault-block, and low-permeability reservoirs in Shengli Oilfield. In addition, some specialized strings were developed to realize pickling (acid-replaceable stratified acidizing strings), integrated acidizing and efficient flowback (acidizing-flowback integrated strings), integrated stratified acidizing and separate water injection (stratified acidizing-separate injection integrated strings), as well as the re-acidizing of a single layer (re-acidizing completion strings). Although these techniques have been widely adopted in the field with satisfied results, they are still far from meeting all the field requirements and the demands for lower cost and higher efficiency. Regarding these shortcomings, some suggestions were put forward including continuous optimization of stratified acidizing strings, further research on multi-functional integrated strings, and deeper studies of intelligent injection techniques and smart strings.
Well Logging & Surface Logging
Research and Application of High-Precision Real-Time Imaging Technology with Near-Bit Gamma
LI Jibo, QIAN Deru, ZHENG Yiting, ZHANG Wei, WU Jinping
2021, 49(3): 135-141.   doi: 10.11911/syztjs.2021022
[Abstract](117) [FullText HTML](46) [PDF 2302KB](56)
The measurement point of the conventional MWD tool is far distant from the bit, and the lithology and dip angle of the formation around the bit cannot be accurately judged in time. This result in a low success rate for drilling formation and a failure to meet the requirements of accurate reservoir description. Therefore, a gamma-ray dynamic formation scanning imaging technology under high-speed conditions, which can realize real-time judgement of the formation lithology under sliding and compound drilling conditions, was studied. In addition, the calculation method realizing the accurate calculation of formation dip angle at the bit was also studied. The high-precision real-time imaging technology with near-bit gamma can image and measure the parameters of near-bit gamma, dynamic well deviation, temperature, and rotation speed in real time, and provide data source for the accurate control of the bit in reservoirs. The field application shows that this technology could meet the needs of geosteering drilling for measurement data, and timely adjust the drilling trajectory through the accurate description of the drilled formation, thus improving the drilling ratio of high-quality reservoirs. The result suggests that the geosteering drilling technology based on domestic near-bit gamma imaging tools deserves wide applications in drilling thin oil layers and those formations with quick dip changes.
Research on Environmental Correction Method of Measurement Results from Near-Bit Gamma Imagers
LI Hongqiang, WANG Ruihe
2021, 49(3): 142-150.   doi: 10.11911/syztjs.2021024
[Abstract](148) [FullText HTML](55) [PDF 4678KB](47)
It is difficult to maintain absolute centering in the wellbore under the actual working conditions of near-bit gamma imagers. For that reason, the environment associated with the original measurement values of gamma sectors in different directions should be corrected according to the eccentricity. Using the principle of gamma imaging and the structural characteristics of the near-bit gamma imager, the influences of the imager eccentricity on the measurement results under different working conditions were studied. The results were used to develop correction charts and methods for the main factors such as attenuation in drilling fluids and compensation in potassium-based drilling fluids when the near-bit gamma imagers were under eccentric condition. The results revealed that the formation dip calculated by the original gamma imaging analysis had a large error due to the influence of drilling fluid in the annulus between the wellbore and the instrument under such condition. In contrast, after environmental correction of near-bit gamma imaging under eccentric condition, the formation dip calculated by the correction method was essentially consistent with the real one. The research results showed that the gamma spectra obtained using near-bit gamma imager under eccentric condition could reflect the real formation after environmental correction, and could calculate the formation dip more accurately.
Interlayer Inversion Method and Its Application Based on Horizontal Well Resistivity Logging
HU Song, WANG Min, TIAN Fei, ZHAO Lei
2021, 49(3): 151-158.   doi: 10.11911/syztjs.2021031
[Abstract](141) [FullText HTML](59) [PDF 2353KB](44)
In order to study the spatial distribution characteristics of interlayers and reveal the distribution pattern of remaining oil, interlayers between wells were predicted and identified. Firstly, the types of interlayers were determined from core analysis, and the identification criteria was established along with logging data.Then, an inversion algorithm was designed on the basis of electric logging for the distribution of interlayers beyond horizontal wellbore. The results demonstrate that the intersection of relative density or relative value of neutron with relative value of gamma can identify two types of interlayers in the target area with absolute errors of 0.018 m and 0.017 m in the inversed thickness of calcareous interlayers and muddy interlayers, respectively. The calcareous interlayers are more developed, with wide distribution and varied change in thickness, while the muddy interlayers are fewer, with a distribution in the northeast orientation. This study, which can provide a reference in studying the distribution and tapping potential of remaining oil, proves that the prediction of interlayer distribution between wells can be more accurate after the interlayer distribution beyond the wellbore is inversed on the basis of horizontal-well resistivity and the inter-well distribution of interlayers determined with the joint control of vertical wells.
Drilling Technology Challenges and Resolutions in Fuling Shale Gas Field
Niu Xinming
2014, 42(4): 1-6.   doi: 10.3969/j.issn.1001-0890.2014.04.001
[Abstract](5768) [PDF 1006KB](4030)
The Key Drilling Technologies in Fuling Shale Gas Field
Ai Jun, Zhang Jincheng, Zang Yanbin, Xu Mingbiao
2014, 42(5): 9-15.   doi: 10.11911/syztjs.201405002
[Abstract](4383) [PDF 1084KB](4040)
Large-Scale Multi-Stage Hydraulic Fracturing Technology for Shale Gas Horizontal Well JY1HF
Zhou Dehua, Jiao Fangzheng, Jia Changgui, Jiang Tingxue, Li Zhenxiang
2014, 42(1): 75-80.   doi: 10.3969/j.issn.1001-0890.2014.01.015
[Abstract](6321) [PDF 1149KB](4193)
Application of Multi-Well Pad in Unconventional Oil and Gas Development in China
Zhang Jincheng, Sun Lianzhong, Wang Jiachang, Zang Yanbin
2014, 42(1): 20-25.   doi: 10.3969/j.issn.1001-0890.2014.01.004
[Abstract](4847) [PDF 1211KB](4020)
Integration Technology of Geology Engineering for Shale Gas Development
Zeng Yijin
2014, 42(1): 1-6.   doi: 10.3969/j.issn.1001-0890.2014.01.001
[Abstract](4670) [PDF 1065KB](4505)
A New Method for Evaluating Shale Fracability Index and Its Application
Jiang Tingxue, Bian Xiaobing, Su Yuan, Liu Shuanglian, Wei Ran
2014, 42(5): 16-20.   doi: 10.11911/syztjs.201405003
[Abstract](3980) [PDF 1055KB](3695)
Status and Prospect of Multi-Well Pad Drilling Technology in Shale Gas
Chen Ping, Liu Yang, Ma Tianshou
2014, 42(3): 1-7.   doi: 10.3969/j.issn.1001-0890.2014.03.001
[Abstract](4261) [PDF 1031KB](3994)
Development and Pilot Test of Hydro-Oscillator
Li Bo
2014, 42(1): 111-113.   doi: 10.3969/j.issn.1001-0890.2014.01.022
[Abstract](4024) [PDF 1085KB](4088)
Development and Reflection of Oil-Based Drilling Fluid Technology for Shale Gas of Sinopec
Lin Yongxue, Wang Xianguang
2014, 42(4): 7-13.   doi: 10.3969/j.issn.1001-0890.2014.04.002
[Abstract](4188) [PDF 1031KB](3650)
Evaluation Model for Shale Brittleness Index Based on Mineral Content and Fracture Toughness
Liao Dongliang, Xiao Lizhi, Zhang Yuanchun
2014, 42(4): 37-41.   doi: 10.3969/j.issn.1001-0890.2014.04.007
[Abstract](3883) [PDF 1143KB](3745)