裂缝干扰下页岩储层压裂形成复杂裂缝可行性

 为认清页岩储层先压开裂缝应力干扰对后续压裂形成复杂裂缝的影响规律，指导页岩储层压裂优化设计，以均质、各向同性的二维平面人工裂缝模型为基础，利用位移不连续理论，推导建立非等裂缝半长、非等间距和任意裂缝倾角的水力裂缝诱导应力干扰数学模型，结合页岩储层复杂裂缝形成的地应力条件，判断不同射孔方式、裂缝参数和原始主应力条件下压裂形成复杂裂缝的可行性。结果表明，分段多簇射孔、多簇同时起裂方式比单段射孔、单段起裂方式应力干扰更强，更利于页岩储层形成复杂裂缝；压开裂缝的长度越长、净压力越大，裂缝诱导应力干扰越强，后续压裂形成复杂缝的可行性越大；距离先压裂缝，存在最利于后续裂缝形成复杂裂缝的位置；原始最大、最小水平主应力差太大的页岩储层利用裂缝应力干扰也达不到有效形成复杂裂缝的地应力条件，不宜将压裂形成复杂裂缝作为储层改造的主要目的。

FEASIBILITY OF FORMATION OF COMPLEX FRACTURES UNDER CRACKS INTERFERENCE IN SHALE RESERVOIR FRACTURING

In order to understand the impact of stress interference caused by the artificial open cracks on the formation of complex fractures of subsequent fracturing，and to guide the optimal design of shale fracturing，a model of stress interference of artificial fractures was established based on the homogeneous and isotropic two-dimensional artificial fracture model. The model considered the displacement discontinuity with the cracks of unequal half-lengths，unequal spacing and arbitrary angles of inclination between cracks and horizontal wellbore to study the feasibility of the formation of complex fractures with different perforations，crack parameters and original principal stress on the basis of geostress conditions. The calculated results indicate that the staged multi-cluster perforation and simultaneous multi-cluster fracture initiation have stronger stress interference for developing complicate fractures than the single-stage perforation and single stage fracture initiation do. The longer length the open cracks，the larger the net pressure and the stronger the interference of fracture induced stress，the greater the possibility of complex fractures formation by the subsequent hydraulic fracturing. The optimal crack spacing between the formal open cracks exists for the formation of complex fractures. Besides，if the difference between the original maximum and minimum horizontal principal stress is too large in shale reservoir，then it?s hard to achieve the geostress condition of complex fracture formation effectively even with the crack interference. So，forming complicate fractures by hydraulic fracturing should not be regarded as the main tool of reservoir stimulation.