页岩气分段压裂水平井非稳态渗流模型

UNSTEADY SEEPAGE MODEL OF THE SHALE-GAS STAGED FRACTURED HORIZONTAL WELL

有关应力敏感页岩气藏分段压裂水平井渗流的解析模型很少,在考虑页岩气吸附解吸附、基质内非稳态扩散及应力敏感的前提下,应用拉式变换、摄动变换、镜像原理以及叠加原理等方法,建立了页岩气分段压裂水平井半解析模型。模型计算结果表明,页岩气分段压裂水平井可分为6个渗流阶段,即线性流、第一径向流、双径向流、天然裂缝系统径向流、窜流阶段和整个系统径向流动。应力敏感主要影响后5个流动阶段,考虑应力敏感的无因次井底压降是不考虑应力敏感的几倍之多,且开发后期无因次压降导数曲线往往上翘,表现出封闭边界影响的特征。如果计算分析时不考虑应力敏感的影响,计算结果会产生较大的误差,且会得出错误的试井解释。所建的半解析模型为快速预测页岩气分段压裂水平井的产能、认识压裂水平井渗流规律和评价分析压裂效果,提供了一种非常有用的方法。

The analytical model is few for the flow of the staged fractured horizontal well in the shale gas reservoir.The calculated results of the model show that the flow can be divided into six stages i. e. linear flow,the first radial flow,double radial flow,radial flow of the natural fracture system,interporosity flow and whole-system radial flow. The dimensionless bottom-hole pressure drop considering the stress sensitivity is several times of that without considering the stress sensitivity,and moreover the dimensionless pressure drop curve often warp in the later period of the development,so the characteristics of the sealed boundary influence are well presented. If do not consider the influence of the stress sensitivity when calculating and analyzing,the calculated results will produce larger error,and furthermore the wrong well test interpretations may be concluded. The built semi-analytical model has pro-vided one useful method for rapid predicting the productivity of the staged fractured horizontal well,understanding the flow laws of the well and evaluating analyzing the effects of the fracturing.