页岩储层复杂裂缝扩展研究

Complex fracture propagation in shale gas reservoir

潘林华 2 张烨 2 陆朝晖 2 邓智 2 柳凯誉³

国土资源部页岩气资源勘查重点实验室（重庆地质矿产研究院），重庆 400042 重庆市页岩气资源与勘查工程技术研究中心
（重庆地质矿产研究院），重庆 400042 中国石油集团公司长城钻探公司井下作业分公司，辽宁 盘锦 124000

页岩储层孔隙度和渗透率低，岩石脆性大，天然裂缝发育。大规模水力压裂过程中，页岩储层易发生张性破坏和剪切破坏相结合的复合破坏，形成复杂网状裂缝，而网状裂缝的展布形态关系到页岩压裂方案的设计和压后产能的评估。针对页岩储层网状裂缝扩展问题，基于流￣固耦合方程和损伤力学原理，建立了二维网状裂缝扩展有限元模型。综合研究认为：水平主应力差增大，压裂裂缝分布长度增加，分布宽度降低，长宽比增大；压裂施工排量降低，压裂裂缝复杂程度降低，压裂裂缝分支数减少，分布长度增加，分布宽度降低，长宽比增大；水平井“多段分簇”压裂可能出现多裂缝干扰问题，部分压裂裂缝在延伸过程中止裂或者沟通两端射孔簇的压裂裂缝；水平井“多段分簇”压裂过程中，各个射孔簇形成的压裂裂缝分支长度差别较大，部分裂缝分支长度明显大于其他裂缝分支。

Combination of tensile failure and shear failure is liable to occur in shale reservoir rock, which will generate complex network fractures in the process of large scale hydraulic fracture, because of the low porosity and permeability, high brittleness and massive natural fractures. Distributing features and fracture geometry of network fracture are related to the design of hydraulic fracturing scheme and the after fracturing productivity prediction. In order to investigate the propagation process of complex fracture network, a two dimensional finite element model is built based on fluid-solid coupling equations in porous medium and theory of damage mechanics. The comprehensive evaluation shows that: the distribution length of network fracture will increase while the distribution width decreases with the increase of the horizontal stress difference, which means the distribution length to width ratio of the network fracture will increase; as the pump rate decreases, the distribution length and the length to width ratio will increase, but the branches, fracture complexity and distribution width will decrease; fractures interference will occur in the process of multiple clusters staged horizontal well, partial fracturing fractures of some perforation clusters will stop propagating or connect the fractures of both ends perforation clusters; there is a great difference in the fracture length of hydraulic fracture generated from every perforation cluster, and the branches of some fractures are much longer than those of the other branches.

10.6056/dkyqt201601020