溶洞是缝洞型碳酸盐岩油藏中主要的储集空间,开采缝洞型油藏的基本思路是通过水力压裂产生裂缝沟通井眼和溶洞。基于TOUGH-AiFrac耦合求解器,分别研究了不同注水压力和溶洞内压对水力裂缝扩展的影响规律。结果表明,随着注水压力的增加,水力裂缝受地应力的影响逐渐减弱,更加倾向于沿着初始方向起裂并扩展。当注水压力大于1.6倍水平最大主应力时,裂缝起裂方向变化幅度明显减小,起裂方向趋于稳定;注水压力大于2.4倍水平最大主应力时,裂缝扩展形态趋于稳定。溶洞内压越大,溶洞对水力裂缝的作用越强,内部压力达到2倍水平最大主应力的溶洞对水力裂缝存在吸引作用,且其吸引作用随着溶洞内压的增加而增强,随着注水压力的增加而减弱。研究成果对于根据储层地质条件优化压裂作业参数提高采收率具有一定的指导意义。

The cave is the main reserve space in fracture-cavity carbonate reservoir. The basic method of fracture-cavity reservoirs exploitation is to generate hydraulic fractures connecting the boreholes and caves through hydraulic fracturing. Based on the TOUGH-AiFrac coupling solver, the influence of different water injection pressures and internal pressure of caves on hydraulic fracture propagation is studied respectively. The results show that with the increase of water injection pressure, the influence of in-situ stress on hydraulic fractures is gradually weakened, and the fractures tend to initiate and propagate along the initial direction. When the water injection pressure is 1.6 times greater than the horizontal maximum principal stress, the rangeability of the fracture initiation directions weaken obviously, and the fracture direction tends to be stable. When the water injection pressure is 2.4 times greater than the horizontal maximum principal stress, the fracture propagation path tends to be stable. The greater internal pressure of the caves, the stronger the cave’s effect on hydraulic fractures. The caves with internal pressure reaching two times of the maximum principal stress exert a kind of “attraction” effect on the hydraulic fractures, which will be gradually strengthened with the increase of cave’s internal pressure while be weakened with the increase of injection pressure. The research results can be used as a guideline to optimize the fracturing work parameters and thereby enhance the oil/gas production rate according to the geological conditions.