首山一矿水平井水力压裂应力阴影效应及裂缝演化机理

Stress shadow effect and fracture evolution mechanism of hydraulic fracturing in horizontal well of Shoushan No.1 Mine

水力压裂是煤层增透和煤层气增产的关键技术,它可有效地造成裂缝网络,增大气体渗流通道面积。然而随着煤层开采深度的增加,煤层气开发面临着埋藏深、赋存环境复杂、岩体致密、非均质性强、开发难度大等难题,水平井段簇方案设计成为解决该问题的关键。基于首山一矿某工作面煤层的物性特征,采用三维有限元应力模拟技术构建地质力学模型,设计储层压裂的排量、液量、液体黏度等压裂工艺技术指标,研究不同应力差对水力压裂半径的影响,并利用该模型运用单因素控制方法,研究分析不同簇间距下裂缝的发育形式与有效半径。研究结果表明,水力压裂工程试验验证了裂缝的有效半径,并且与数值模拟分析结果相吻合;随着地应力差异系数的增大,水力压裂主裂缝逐渐发生偏移,水平应力差越小,形成的压裂缝网越复杂;随着簇间距的增加,裂缝的簇间应力干扰作用减弱,裂缝的扩展变得更加均匀。

Hydraulic fracturing is a key technology for improving the permeability of coal seam and increasing the production of coalbed methane.It can effectively create fracture network,increase the area of gas seepage channel.However,with the increase of coal seam mining depth,coalbed methane development faces challenges such as deep burial,complex occurrence environment,dense rock mass,strong heterogeneity,and high development difficulty.The design of horizontal well cluster scheme has become the key to solving this problem.Based on the physical properties of a coal seam in a certain working face of Shoushan No.1 Mine,a geomechanical model was constructed using three-dimensional finite element stress simulation technology.The fracturing process technical indicators such as reservoir fracturing displacement,liquid volume,and liquid viscosity were designed to study the influence of different stress differences on the hydraulic fracturing radius.Using this model and single factor control method,the development form and effective radius of fractures under different cluster spacings were studied and analyzed.The results showed that the effective radius of fracture was verified by hydraulic fracturing engineering test and was in agreement with the numerical simulation analysis results.With the increase of the difference coefficient of ground stress,the main fracture of hydraulic fracture gradually migrated,and the smaller the horizontal stress difference was,the more complex the compression fracturing network formed.With the increase of the cluster spacing,the intercluster stress interference of fractures decreased,and the propagation of cracks became more uniform.