沁水盆地南部地应力场特征及其研究意义

采用水压致裂测量地应力方法，测得了沁水盆地南部45口煤层气井主采煤层地应力分布，通过统计分析，建立了主采煤层地应力与煤层埋藏深度之间的相关关系和模型，分析了地应力在煤储层渗透性及压裂研究中的意义。研究结果表明：沁水盆地南部最大水平主应力为642~4186 MPa，平均为1721 MPa；最大水平主应力梯度为117~479 MPa/100 m，平均为264 MPa/100 m；最小水平主应力330~2640 MPa，平均为11391 MPa；最小水平主应力梯度为099~285 MPa/100 m，平均为177 MPa/100 m。主应力均随着煤层埋藏深度的增大而增高，呈线性关系。在650 m以浅煤储层地应力状态主要表现为σv＞σhmax ＞σhmin，最小水平主应力小于12 MPa，现今地应力状态处于伸张带；在650~1 000 m煤储层地应力状态转化为σhmax ≈σv≈σhmin，最小水平主应力为12~20 MPa，现今地应力状态由伸张带转化为压缩带的过渡；在1 000~1 500 m煤储层地应力状态为σhmax ≈σv≈σhmin，最小水平主应力大于20 MPa，现今地应力状态转化为压缩带。在地应力的作用下，裂缝逐渐趋于闭合,煤储层渗透率急剧下降。同时，地应力对煤储层水力压裂裂缝扩展产生重要影响，水力压裂裂缝均沿着最大主应力方向扩展。

Characteristics of In-situ Stress Field in Southern Qinshui Basin and Its Research Significance

Adopted hydraulic fracturing method to measure in-situ stress, obtained in-situ stress distribution of main minable coal seams of 45 coalbed methane testing wells in South Qinshui Basin, through statistical analysis, the correlations and their models between in-situ stress in main minable coal seams and the burial depth of coal seam are established, the significance of in-situ stress in research of coal reservoir’s permeability and hydraulic fracturing is analysised. The result shows that the maximum horizontal principal stress in Southern Qinshui Basin is 6.42-41.86MPa, the average is 17.21MPa, the maximum horizontal principal stress grads is 1.17-4.79MPa/100m, the average is 2.64MPa/100m; the minimum horizontal principal stress is 3.30-26.40MPa, the average is 11.391MPa,the minimum horizontal principal stress grads is 0.99-2.85MPa/100m, the average is1.77MPa/100m. It is also noticed that principal stresses all increase following a linear relationship as coal seam burial depth increase. The coal reservoirs with a burial depth shallower than 650m, in-situ stress state principally shows , the minimum horizontal principal stress is below 12MPa, recent in-situ stress state is located tension zone, the in-situ stress state of coal reservoirs with 650-1000m in depth transforms into , the minimum horizontal principal stress is 12-20MPa, recent in-situ stress state is situated transition zone which transforms from tension zone into compression zone, the coal reservoirs with 1000-1500m in depth, in-situ stress state is , the minimum horizontal principal stress is over 20MPa, recent in-situ stress state becomes compression zone. Under the effect of in-situ stress, fissures are tend to closed gradually, and the coal reservoir’s permeability droped rapidly . Simultaneity, in-situ stress produced an important influence on crack propagation of coal reservoir’s hydraulic fracturing, direction of crack propagation is all along the maximum horizontal principal stress’s.