超临界CO<sub>2</sub>萃取页岩油效果评价及影响因素分析

李邦国; 侯家鵾; 雷兆丰; 张博; 王斌; 陈江

doi:10.11911/syztjs.2024069

超临界CO₂萃取页岩油效果评价及影响因素分析

李邦国^1,,
侯家鵾¹,
雷兆丰¹,
张博²,
王斌³,
陈江^3, ,

1.
中国石油长庆油田分公司第六采油厂，陕西榆林 718600
2.
中国石油长庆油田分公司第三采油厂，宁夏银川 750006
3.
中国石油长庆油田分公司勘探开发研究院，陕西西安 710016

基金项目: 国家科技重大专项“鄂尔多斯盆地大型低渗透岩性地层油气藏开发示范工程”（编号：2016ZX05050）资助。

详细信息

作者简介:
李邦国（1989—），男，甘肃武威人，2012年毕业于中国石油大学（华东）资源勘察工程专业，工程师，主要从事油田开发工作。E-mail：499797885@qq.com

通讯作者:
陈江，331579261@qq.com

中图分类号: TE357.45
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出版历程
- 收稿日期: 2022-11-08
- 修回日期: 2024-07-10
- 网络出版日期: 2024-07-22
- 刊出日期: 2024-08-25

Evaluation of Shale Oil Extraction by Supercritical CO₂ and Analysis of Influencing Factors

1.
The No.6 Oil Production Plant, Petrochina Changqing Oilfield Company, Yulin, Shaanxi, 718600, China
2.
The No.3 Oil Production Plant, Petrochina Changqing Oilfield Company, Yinchuan, Ningxia, 750006, China
3.
Research Institute of Exploration and Development, PetroChina Changqing Oilfield Company, Xi’ an, Shaanxi, 710016, China

摘要

摘要:
为明确裂缝及压力对超临界CO₂萃取页岩油的影响机理，在获取试验用页岩岩样孔径分布、比表面积和孔体积的基础上，进行了超临界CO₂岩样萃取试验，采用改进的磁悬浮天平高压吸附仪，实时测定了高温高压下页岩岩样质量的变化；并结合页岩核磁共振T₂谱，精确测定了超临界CO₂对页岩油的萃取效率，明确了萃取过程中页岩孔隙动用特征及动用孔径下限。试验结果表明，目标储层页岩中介孔（孔径2～50 nm）发育程度最高，占总孔隙体积和总比表面积的69.72%和73.47%；而大孔（孔径＞50 nm）发育程度最差，仅占总孔隙体积和总比表面积的4.45%和10.77%。原油主要赋存于孔径1.4～120.0 nm的小孔径孔隙中，CO₂对大孔径（＞86 nm）孔隙中原油的萃取效果高于小孔径（≤86 nm）孔隙；裂缝能够增大CO₂与基质中页岩油的接触面积，加快油气传质速度，提高基质动用深度，降低页岩油渗流阻力和孔隙动用下限。然而，CO₂萃取效率除与裂缝数量相关外，还受基质渗透率及裂缝−基质连通特征的影响。CO₂动用孔隙孔径下限随注入压力升高而降低，由8 MPa时的6.54 nm减小至18 MPa的3.27 nm。研究成果可为注CO₂提高页岩油采收率提供借鉴。
- 页岩油 /
- 裂缝 /
- CO₂ /
- 注入压力 /
- 核磁共振 /
- 萃取效率 /
- 称重法
Abstract:
To define the influence mechanism of fractures and pressure on the extraction of shale oil by supercritical CO₂, the core extraction experiment by supercritical CO₂ was conducted on the basis of identifying the pore size distribution, specific surface area, and pore volume of experimental shales. The improved magnetic suspension balance high pressure adsorption instrument was used to measure the shale mass change under high temperature and pressure in real time. Combined with the nuclear magnetic resonance (NMR) T₂ spectrum of shale, the extraction efficiency of shale oil by supercritical CO₂ was accurately measured, and the producing characteristics of shale pores and the lower limit of producing pore size in the extraction process were defined. The experimental results show that the target reservoir shale mesopore (pore size of 2~50 nm) is the most developed, accounting for 69.72% and 73.47% of the total pore volume and total specific surface area. However, macropores (>50 nm) are the least developed, accounting for only 4.45% and 10.77% of the total pore volume and total specific surface area. The crude oil mainly exists in the pores with a small pore size of 1.4~120 nm. The extraction effect of CO₂ on the crude oil in the pores with large pore size (>86 nm) is better than that in the pores with small pore size (≤86 nm). Fractures can increase the contact area between CO₂ and shale oil in the matrix, accelerate the mass transfer rate of oil and gas, improve the depth of matrix production, and reduce the shale oil seepage resistance and the lower limit of pore production. However, the CO₂ extraction efficiency is not only related to the number of fractures but also affected by matrix permeability and fracture-matrix connectivity. The lower limit of pore size for CO₂ production decreases with the increase in injection pressure from 6.54 nm at 8 MPa to 3.27 nm at 18 MPa. The research findings provide a reference for enhancing the recovery rate of shale oil by injecting CO₂.
- shale oil /
- fractures /
- CO₂ /
- injection pressure /
- NMR /
- extraction efficiency /
- weighing method

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图 1 改进的磁悬浮天平高压吸附仪示意

Figure 1. Improved magnetic suspension balance high pressure adsorption instrument

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图 2 裂缝岩样切割示意

Figure 2. Cutting of fractured rock samples

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图 3 试验页岩岩样低温氮气吸附解吸曲线

Figure 3. Adsorption and desorption curves of low temperature nitrogen in experimental shale samples

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图 4 试验页岩岩样的孔径分布

Figure 4. Pore size distribution of experimental shale samples

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图 5 4个试验页岩岩样CO₂萃取前后的T₂谱分布

Figure 5. T₂ spectrum distribution of four experimental shale samples before and after CO₂ extraction

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图 6 CO₂萃取后4个页岩岩样中部沿裂缝平行切面的核磁共振成像对比

Figure 6. NMR imaging comparison of parallel sections along fractures in the middle of four shale samples after CO₂ extraction

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图 7 CO₂萃取后4个页岩岩样靠近顶部端面2 cm处纵向切面的核磁共振成像对比

Figure 7. NMR imaging comparison of longitudinal sections 2 cm from the top end face of four shale samples after CO₂ extraction

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图 8 不同CO₂注入压力下1#页岩岩样T₂谱的变化

Figure 8. Variation of T₂ spectrum of 1# shale samples under different CO₂ injection pressures

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图 9 实时称重法和NMR法获得的CO₂萃取效率与CO₂注入压力之间的关系

Figure 9. Relationship between CO₂ extraction efficiency and injection pressure by real-time weighing method and NMR method

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表 1 试验用页岩岩样的基本物性参数

Table 1 Basic physical parameters of experimental shale samples

岩样编号	孔隙度，%	渗透率/mD	有机碳含量，%	热成熟度，%	矿物组分及含量，%
岩样编号	孔隙度，%	渗透率/mD	有机碳含量，%	热成熟度，%	石英	钠长石	方解石	白云石	黄铁矿	黏土矿物
1#	5.62	0.004 47	3.52	2.31	26.3	4.5	9.4	3.4	2.7	53.7
2#	6.38	0.006 56	3.18	2.04	41.7	4.4	15.1	3.1	4.8	30.9
3#	6.15	0.007 52	4.22	2.27	37.2	4.1	11.4	2.7	3.5	41.1
4#	5.62	0.003 81	3.06	2.14	29.7	5.7	8.6	4.2	3.3	48.5

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表 2 低温氮气吸附试验测得页岩岩样的孔隙结构参数

Table 2 Measurement of pore structure parameters of experimental shale samples by low temperature nitrogen adsorption experiment

样品编号	BJH孔体积/（μL·g⁻¹）	平均孔径/nm	不同孔径孔隙体积占总孔隙体积的比例，%			BET比表面积/ （m²·g⁻¹）	不同孔径孔隙比表面积占总孔隙比表面积的比例，%
样品编号	BJH孔体积/（μL·g⁻¹）	平均孔径/nm	＜2 nm	2～50 nm	＞50 nm	BET比表面积/ （m²·g⁻¹）	＜2 nm	2～50 nm	＞50 nm
1	22.47	6.26	30.92	63.42	5.67	1.44	18.81	69.38	11.81
2	26.98	6.34	20.54	74.48	4.98	2.05	14.92	72.03	13.05
3	29.79	7.28	24.34	72.64	3.03	2.93	12.64	79.97	7.39
4	24.64	6.05	27.52	68.35	4.13	1.76	16.71	72.48	10.81
均值	25.97	6.48	25.83	69.72	4.45	2.05	15.77	73.47	10.77

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表 3 采用实时称重法和NMR法计算CO₂萃取效率的对比

Table 3 Calculation of CO₂ extraction efficiency by real-time weighing method and NMR method

岩心编号	岩心质量/g		饱和原油量/mL	CO₂萃取效率，%
岩心编号	萃取前	萃取后	饱和原油量/mL	实时称重法	NMR法
1#	61.86	61.65	0.57	37.00	39.89
2#	56.59	56.20	0.66	58.68	60.43
3#	60.10	59.58	0.71	73.04	74.29
4#	58.46	58.09	0.61	60.43	61.65

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