煤系页岩储层水力裂缝穿层扩展规律

Hydraulic fracture height growth law for deep coal measures shale reservoir

付世豪,陈勉,夏阳,谭鹏,张雨晴,李英杰

中国石油大学（北京）石油工程学院，北京 102249 中国石油工程技术研究院有限公司，北京 102206

深部煤系页岩储层纵向上连续发育多套产层，由于对裂缝扩展形态认识不清，缝高延伸距离短，一体化水力压裂作业无法沟通不同产层。为了提升水力裂缝纵向延伸能力，基于有限元计算平台，采用最大主应力起裂准则，考虑压裂液沿裂缝面横向和纵向流动规律，建立了煤系页岩层状储层水力裂缝三维穿层扩展模型，并研究了层间渗透率差异、主应力条件及岩性界面等多因素对裂缝穿层规律的影响。研究结果表明：根据与岩性界面作用方式的不同，水力裂缝呈现出T形缝、穿层缝、钝化缝和十字缝等4种典型形态；随着层间渗透率差异系数的增大，水力裂缝穿层能力不断降低；层间应力差越小，裂缝穿透岩性界面进入相邻层位的概率越大；当高渗透率隔层和低渗透率储层的渗透率差异系数高于5，或者层间最小水平主应力差高于4 MPa时，缝高延伸至岩性界面，停止扩展。

There are many types of gas bearing layers alternately developed vertically in deep coal measures shale reservoir. However, the fracture geometries are unclear, the distance of fracture height extension becomes short and different pay layers cannot be communicated in integrated hydraulic fracturing. In order to improve the propagation ability of fracture height, the maximum principal stress fracture extension criteria is introduced and the lateral and longitudinal flow of fracturing fluid along the fracture surface is considered. A 3D hydraulic fracture propagation numerical model is built in finite element calculation platform. The effect of permeability difference, in-situ stress condition and lithological interface on the hydraulic propagation are mainly studied. The results show that the fracture geometries could be classified into four categories according to interaction type between hydraulic fracture and lithological interface: T shaped fracture, penetrated fracture, deactivated fracture and + shaped fracture. The ability of hydraulic fracture crossing lithological boundary is decreasing with the increase of high permeability difference coefficient. In addition, with small interlayer stress difference, the probability of fracture penetrating interface and propagating into adjunct layer is greater. when permeability difference coefficient is great than 5 and minimum horizontal principal stress difference is larger than 4 MPa, the fracture reaches to the lithological interface and then stop propagating in the vertical direction.

10.6056/dkyqt202104023