沁水盆地西南缘煤层气水力压裂裂缝分布特征及主控因素研究

Distribution characteristics and main controlling factors of hydraulic fracturing fractures of coalbed methane in the southwestern margin of Qinshui Basin

基于沁水盆地西南缘安泽地区7口煤层气井的水力压裂裂缝微震监测数据,结合煤岩样品测试、测井、压裂等资料,揭示研究区水力压裂裂缝分布特征,探讨水力压裂裂缝扩展主控因素。研究结果表明:研究区压裂裂缝展布方向主要为NE—SW、NEE—SWW向,优势方位为NEE—SWW向;煤层压裂裂缝扩展长度介于150~210 m,平均175 m,裂缝影响宽度为28~35 m,平均30 m,裂缝高度为9~20 m,平均15 m;煤储层压裂裂缝分布受控于地应力、煤岩及顶底板岩石力学性质、煤岩煤质特征、压裂规模等因素,裂缝扩展方向和最大地应力方向一致;煤岩杨氏模量、切变模量越小,裂缝长度越长,裂缝影响宽度及高度越小;煤岩泊松比越小,裂缝长度越短,裂缝影响宽度及高度越大;裂缝高度、影响宽度受煤岩与顶底板岩石力学性质影响,煤岩与顶底板岩石力学性质差异越大,裂缝高度、影响宽度越大;水力压裂规模(液量、砂量)越大,压裂效果越明显;煤储层压裂裂缝几何形态以垂直裂缝为主,煤储层中裂缝几何形态受控于地层中三向主应力的相对大小。

Based on microseismic monitoring data of hydraulic fracturing fractures in the 7 coalbed methane wells in the Anze area of the southwestern margin of the Qinshui Basin,combining with coal rock sample testing,logging,fracturing and other data,the distribution characteristics of hydraulic fracturing fractures in the area were revealed,and the main controlling factors for hydraulic fracturing fracture expansion were explored.The research results indicate that,the main distribution directions of fracturing fractures in the area are NE-SW and NEE-SWW directions,with the dominant direction being NEE-SWW direction;The fracture propagation length of coal seam hydraulic fracturing is 150~210 m,with an average of 175 m,the impact width of the fracture varies from 28~35 m,with an average of 30 m,and the fracture height varies from 9-20 m with an average of 15 m.The distribution of fractures in coal reservoirs is controlled by factors such as in-situ stress,mechanical properties of coal and roof and floor,characteristics of coal and coal quality,and fracturing scale.The direction of fracture propagation is consistent with the direction of in-situ stress;The smaller the variable modulus,the longer the length of the crack,the smaller the width and height of the crack;the smaller the Poisson's ratio of coal and the shorter the length of the crack,the greater the width and height of the crack;the height and width of the crack are controlled by the coal and rock Compared with the mechanical properties of roof and floor rocks,the greater the difference between the mechanical properties of coal and roof and floor rocks,the greater the height and width of the cracks.The larger the hydraulic fracturing scale(liquid volume,sand volume),the more obvious the fracturing effect.The characteristics of coal rock and coal quality have a certain indirect influence on the fracturing of coal reservoirs.The geometry of hydraulic fracturing fractures in coal reservoirs is dominated by vertical fractures,and the geometry of fractures in coal reservoirs is controlled by the relative magnitude of the three-dimensional principal stresses in the formation.