页岩气水平井组拉链压裂过程中地应力的分布规律

页岩储层具有低孔隙度、超低渗透率的特征，往往需要通过水力压裂才能使气井具备一定的生产能力。拉链压裂是近年来针对页岩气藏缝网压裂的一项新兴工艺，为了认清压裂过程中裂缝应力干扰后地应力场的分布规律并给页岩压裂设计提供参考，首先假设地层为均质、各向同性弹性体，然后通过位移不连续法，建立起地层应力场分布数学模型，并利用线性叠加原理，得到人工裂缝周围水平应力场的分布情况。研究发现：①裂缝周围的地应力随着与裂缝距离的远近有不同程度的增加；②裂缝尖端处存在应力集中现象，且在裂缝尖端附近产生的拉应力使得水平应力有所减小；③裂缝对水平最小主应力的影响程度大于对最大主应力的影响；④随着裂缝条数的增加，诱导应力的叠加干扰对水平主应力的影响不断增强，且水平应力差异性逐渐减小；⑤在裂缝交错排列的区域内，应力干扰较强，应力场分布较复杂。上述研究成果对页岩气水平井组拉链压裂的优化设计具有指导意义。

Distribution rules of earth stress during zipper fracturing of shale gas horizontal cluster wells

Shale reservoirs are characterized by low porosity and ultra-low permeability, so hydraulic fracturing is generally necessary to realize production capacity of shale gas wells. Zipper fracturing is an emerging technology for shale gas network fracturing. In order to understand the distribution rules of earth stress field under the interference of fracture stress during fracturing and to provide guides for shale fracturing design, a mathematical model of in-situ stress field distribution was established by using displacement discontinuity method while the formation is assumed as the homogeneous and isotropic elastomer. Then, the distribution of horizontal stress fields around hydraulic fractures was recognized by using linear superposition principle. It is indicated that the earth stress around the fractures rises in different degrees, depending on its distance from the fractures. Stress accumulation occurs at fracture tips. Horizontal stress decreases to some extent due to the tension stress generated in the periphery of fracture tips. The effect of fractures on minimum horizontal principal stress is more than that on maximum principal stress. The greater the number of the fractures is, the more effect of superposition interference the induced stress has on horizontal principal stress and the less the horizontal stress contrast is. Stress interference is stronger and stress field distribution is more complex in the region where fractures intersect. The research findings in this paper play an important role in the optimized design of zipper fracturing in shale gas horizontal cluster wells.