深层缝洞型碳酸盐岩储层水力裂缝扩展机理研究

Mechanism of Hydraulic Fracture Propagation in Deep Fracture-Cavity Carbonate Reservoirs

为了准确掌握深层缝洞型碳酸盐岩油藏压裂过程中水力裂缝的扩展规律,基于弹性力学、断裂力学和流–固耦合理论,建立了适用于缝洞型储层的水力裂缝扩展数学模型,采用数值模拟方法分析了水力裂缝扩展过程与缝洞体的相互作用规律,并对“沿缝找体”压裂技术的适用性进行了深入探讨。数值模拟结果表明:溶洞周围发育天然裂缝时,会影响缝洞体周围局部诱导应力场,使水力裂缝更容易沟通缝洞体;采用大排量注入低黏压裂液或中小排量注入高黏压裂液,仅能沟通与水力裂缝初始扩展方向夹角较小的溶洞,而对与水力裂缝初始扩展方向夹角较大的溶洞,则需考虑采用强制转向技术进行沟通。研究结果表明,基于井眼与缝洞体的配置关系,采用“沿缝找体”压裂技术可以实现直接沟通、定向沟通和沿缝沟通3种缝洞体沟通模式,显著扩大储量动用范围。

In order to understand the law of hydraulic fracture propagation in deep fracture-cavity carbonate reservoirs during the fracturing process,a mathematical model of hydraulic fracture propagation suitable for fracture-cavity reservoirs was established based on elastic mechanics,fracture mechanics,and fluid-solid coupling theory.On the basis of the model,a numerical simulation was carried out to analyze the interaction law between hydraulic fractures and fracture-cavity reservoirs during propagation,and the technical applicability of“cave connection by natural fractures”was discussed thoroughly.The numerical simulation results show that the locally induced stress field around the fracture-cavity reservoir will be affected when natural fractures develop around the cave,which makes it easier for hydraulic fractures to connect with the fracture-cavity reservoir.The injection of low-viscosity fracturing fluid at large displacement or high-viscosity fracturing fluid at medium and small displacement can only connect to caves that have a small angle with the initial hydraulic fracture propagation direction,while for caves with large angles,forced steering technology should be considered for connection.The results show that according to the distribution relationship between wellbore and fracture-cavity reservoirs,three fracture-cavity reservoir connection modes including direct connection,directional connection,and seam connection can be achieved by using the technique of“cave connection by natural fractures”,which significantly improves the production range of reserves.