盐间页岩油多岩性交互储层破裂及裂缝扩展机理研究

Mechanism of reservoir breakdown and fracture propagation of inter-salt shale oil with muitiple lithologic layers

  • 摘要: 针对江汉盆地潜江凹陷盐间页岩油多岩性交互储层非均质性强、层理复杂、裂缝扩展机理不清、压裂改造难度大的问题,以该区典型多岩性交互储层为研究对象,依托真三轴水力压裂物理模拟试验,遵循注入排量、地应力、能量三大相似准则,系统开展了岩性组合、弹性模量、界面强度、压裂液类型、注入排量与黏度对裂缝起裂及扩展的控制机制研究,结合灰色关联法明确主控因素权重,并开展了现场井试验验证。结果表明:盐间页岩油储层相较于常规页岩储层新增盐岩溶蚀扩展机制,共形成6类裂缝扩展模式;裂缝易由高弹性模量层向低弹性模量层贯穿,低强度岩性界面易诱导裂缝转向耗能;超临界CO2与醇基压裂液可有效抑制盐岩溶蚀、降低破裂压力,小排量低黏度利于形成复杂缝网,大排量高黏度可促进裂缝穿层延伸;各因素影响权重依次为压裂液与岩石相互作用>弹性模量>注入排量>界面强度>压裂液黏度。现场采用“前置CO2+多簇密切割高强度压裂+梯提排量+高黏稳压力+闷井渗吸”压裂模式,可有效规避井筒结盐风险、扩大缝控改造体积,试验井增产效果显著。研究成果可为盐间页岩油多岩性交互储层高效压裂开发提供理论支撑与工艺参考。

     

    Abstract: This study addresses the unclear fracture behavior and unsatisfactory fracturing effects in the multi-lithologic-layers interactive reservoirs of salt-interbedded shale oil. Using the Qianjiang Formation reservoir in the Jianghan Basin as a research object, true triaxial hydraulic fracturing experiments were conducted to investigate the fracture breakdown and propagation mechanisms. The results show that fracture propagation patterns can be classified into six types: through-and-turn, through-without-turn, turn-without-through, without-turn-without- through, dissolution-and-through, and dissolution-without-through. The core mechanism of fracture propagation lies in the dynamic coupling between the lithology interface and the stress field. The sensitivity ranking of the influencing factors is as follows: fluid-rock interaction > elastic modulus > injection rate > interface strength > fracturing fluid viscosity. The study also reveals that for every 10 MPa increase in elastic modulus difference, fracture height and length increase by 0.58 cm and 0.43 cm, respectively. For every 1 MPa increase in interface strength, fracture height increases by 0.28 cm, while fracture length decreases by 1.81 cm. Compared to water-based and alcohol-based fracturing fluids, SC-CO2 fracturing fluid reduces the fracture pressure by 32% and 24%, respectively. For every 1 mL/min increase in single-cluster injection rate, fracture length increases by 0.06 cm. Additionally, for every 10 mPa·s increase in fracturing fluid viscosity, fracture height and length increase by 0.20 cm and 0.07 cm respectively. This study provides a theoretical basis for the efficient development of multi-lithologic-layers interactive reservoirs in salt-interbedded shale oil and offers important guidance for on-site fracturing operations.

     

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