裂缝性页岩气藏渗流特征与压力动态分析

为研究页岩气直井压裂后的复杂渗流机理，采用分形理论来表征裂缝的发育特征，结合页岩气的解吸和扩散等流动特征，建立了页岩气分形气藏压裂直井的三线性流模型，求得了考虑井筒存储和表皮效应的压裂直井的拉普拉斯空间解析解，通过数值反演得到了其数值解；分析了页岩气解吸、天然裂缝发育情况等因素对压力曲线的影响。计算结果表明：井筒储集系数影响曲线的早期续流段；人工裂缝导流能力不仅影响人工裂缝的线性流动阶段，同时还影响天然裂缝的线性流动阶段；串流系数影响压力导数曲线“下凹”时间；弹性储容比和解吸系数决定压力导数曲线“下凹”深浅；分形维数影响地层双线性流动。最后验证了模型的可靠性。

Pressure transient analysis of fractured shale gas flow and seepage characteristics

In order to study the mechanism of shale gas in vertical fractured wells,by using the fractal theory to charac-terize the crack growth characteristics,combined with shale gas desorption and diffusion flow characteristics,we establish an analytical trilinear seepage flow model of vertical fractured wells.The Laplace space solution of dimensionless bottom hole pressure is achieved considering wellbore storage and skin effect.Type curves of dimensionless pressure and derivative are poltted with stehfest algorithm.The study result showed that wellbore storage coefficient mainly affects the early freew heeling segment of the curve;artificial fractured conductivity not only affects the artificial fracture linear flow stage,but also affects the natural fracture linear flow stage;cross -flow coefficient decides concave time of pressure derivative curve;stor-age capacity ratio and desorption coefficient influence the hollows width and depth of the pressure derivative curve;fractal index mainly formation bilinear flow.Therefore,the results of this study can be used for pressure dynamic analysis and e-valuation capacity of shale gas reservoir.