页岩气藏压裂水平井试井分析

页岩气藏资源丰富,开发潜力巨大,已成为目前研究的热点.与常规气藏相比,页岩气藏运移机制复杂,流动模式呈非线性,有必要考虑页岩气的吸附解吸,天然微裂缝的应力敏感性,人工裂缝内的非达西流等非线性因素对压裂水平井压力响应的影响. 基于双重介质和离散裂缝混合模型,分别采用Langmuir等温吸附方程描述吸附解吸,渗透率指数模型描述应力敏感,Forchheimer方程描述非达西效应,建立页岩气藏压裂水平井数值试井模型. 运用伽辽金有限元法对模型进行求解.根据试井特征曲线,划分流动阶段,着重分析非线性因素对压力响应的影响.结果表明:页岩气藏压裂水平井存在压裂裂缝线性流、压裂裂缝径向流、地层线性流、系统径向流及封闭边界影响5 种流动阶段.吸附解吸的影响发生窜流之后,Langmuir吸附体积增大,拟压力导数曲线凹槽更加明显,系统径向流出现时间与压力波传播到边界时间均延迟;天然裂缝系统的应力敏感性主要影响试井曲线的晚期段,拟压力和拟压力导数曲线均表现为上翘,应力敏感效应越强,上翘幅度越大;高速非达西效应对早期段影响较大,非达西效应越强,拟压力降幅度越大,试井曲线上翘.与解析解的对比以及矿场实例验证了模型的正确性与适用性. 

PRESSURE TRANSIENT ANALYSIS OF FRACTURED HORIZONTAL WELL IN SHALE GAS RESERVOIR

Shale gas reservoirs have received much attention for their potential in satisfying future energy demands. Compared to conventional gas reservoir, Shale gas reservoir is characterized by complicated nonlinear processes, including adsorption and desorption, pressure-dependent permeability and non-Darcy flow. To investigate the e ect of those nonlinear mechanisms, a combined dual-continuum and discrete fracture numerical well test model was developed to analyze the transient pressure. Desorption, pressure-dependent permeability of natural fractures and non-Darcy flow was respectively described by Langmuir isotherm equation, exponential model of permeability and Forchheimer equation. Galerkin finite element method was applied to solve the model. Flow regimes were divided and the e ect of nonlinear factors on pressure response was analyzed according to the well test curve. The results indicate that there are five flow regimes, including fracture linear flow, fracture radial flow, formation linear flow, formation radial flow, pseudo steady state of closed boundary. The shale gas desorption's e ect arising after interporosity flow happened, the bigger Langmuir adsorption volume is, the deeper groove shows on the derivative curve and the later pressure propagate to the border; Bigger pseudo-pressure drop and pseudo-pressure derivative were observed with greater pressure-dependent e ect in the later stage of well test curve; Non-Darcy flow in hydraulic fractures mainly a ecting the early time, the pseudo-pressure drop increased with increasing flow rate. The comparison with analytical solution and field engineering application prove the feasibility of the model.