采用过采空区的煤层气井抽采下伏煤层甲烷可以降低矿井瓦斯灾害风险.实现煤与煤层气共采.具有良好的应用前景.采空区下伏煤层应力分布是过采空区煤层气井开发效果的关键影响因素之一.而目前相关的研究鲜有报道.以山西晋城矿区寺河井田东区为例.基于地应力测试与压裂施工数据.分析了3号煤采空区下伏煤层应力.压裂工艺参数特征及采动井的产气效果.结果表明.研究区未采动的3号煤层应力为走滑断层应力机制.即最大水平主应力SHmax＞垂直应力Sv＞最小水平主应力Shmin.其向斜轴部存在应力集中.最小主应力及压裂施工压力高.破裂压力与施工压力之差较小,而3号煤的开采导致采空区下伏的9号.15号煤层的上覆荷载降低.3号煤层采空区下伏的9号.15号煤层水平应力与垂向应力之比高于未采动煤层,未采动井的破裂压力与施工压力之差为-4.9-11.7 MPa.平均值为2.14 MPa,采动井的破裂压力与施工压力之差为0.5-18.0 MPa.平均值为7.1 MPa,采动煤层的破裂压力与施工压力之差明显大于未采动煤层.采动煤层的破裂压力梯度高于未采动煤层.而采动煤层的施工压力梯度低于未采动煤层,位于采空区下方背斜轴部的煤层施工压力与破裂压力之差较大.渗透性相对较好,处于保护层煤柱下方的煤层段存在应力集中效应.破裂压力与施工压力之差较小.渗透性较差.但经过地面井压裂增透后.可以取得较好的产气效果.日产气量可达4 224 m3.

Extracting the coalbed methane underlying the goaf by surface boreholes through the goaf can reduce the risk level of coal mine gas disaster and realize the co-mining of coal and coalbed methane,which has a good application prospect. Stress distribution in coal seams underlying a goaf is one of the key considerations that affect the production of coalbed methane well through the goaf,but at present,relevant research reports are rare. Taking the eastern Si-he coalfield in the Jincheng mining area Shanxi Province as an example,based on the in-situ stress measurement results and hydraulic fracturing data,the characteristics of stress and hydraulic fracturing parameters of the coal seams underlying the No.3 coal seam in the study area were analyzed and the influence of the coal mining on the gas production of the underlying coal seams was discussed. The results showed that,the stress of No.3 coal seam in the study area fell into a strike-slip faulting stress regime,that is,SHmax>Sv>Shmin,In No.3 coal seam,the stress concentration existed in the syncline axis part where the least principal stress and the fracture propagation pressure were abnormally high,and the difference between the formation breakdown pressure and the fracture propagation pressure was relatively low,the extraction of No.3 coal seam resulted in a drop in overlying load of No. 9 and No. 15 coal seams,and therefore the ratios of horizontal stress to vertical stress of No.9 and No.15 coal seams under No.3 coal seam goaf were higher than those of coal seams that were not affected by mining. For the coalbed methane wells in the unexploited areas,the difference between the formation breakdown pressure and the fracture propagation pressure ranged from -4.9-11.7 MPa,averagely 2.14 MPa,for the coalbed methane wells in the mining-affected areas,the difference between the formation breakdown pressure and the fracture propagation pressure ranged from 0.5-18.0 MPa,averagely 7.1 MPa,and the formation breakdown pressure gradient were obviously higher in the mining-affected coal seams than that in the coal seam that were not affected by mining,and the fracture propagation pressure gradient was lower in the mining-affected coal seam than in the intact coal seam,the coal seam under the goaf and in the anticline axis part had a high pressure difference between the fracture propagation pressure and the formation breakdown pressure and a relatively high permeability,due to the effect of stress concentration,the coal seam under the coal pillar of the protective layer had a low permeability and a low difference between the fracture propagation pressure and the formation breakdown pressure while a high gas production of up to 4 224 m3/d can be achieved from these sections after stimulation by hydraulic fracturing through the surface well.

1 地质背景

2 储层应力确定方法

   2.1 垂直应力的估算

   2.2 主应力测试

   2.3 基于摩擦平衡理论的主应力估算

3 结果与讨论

   3.1 主应力与应力机制

   3.2 施工压力与破裂压力

4 讨论

   4.1 采动卸压作用影响范围

   4.2 储层应力与所处构造部位的关系

   4.3 采动井产气特征

5 结论