致密气藏压裂水平井不稳态压力分析

采用离散化裂缝模型,裂缝内考虑为变质量流,利用叠加原理得到气藏内任一点压降计算式,在裂缝壁面处耦合裂缝内流动与气藏内流动,得到致密气藏压裂水平井不稳态压力分析模型。分析了无因次拟压力导数的斜率对应的物理意义,将不稳态渗流过程划分为5个具体阶段:裂缝内线性流阶段、裂缝间线性流阶段、气藏内早期径向流阶段、气藏内线性流阶段和气藏内晚期径向流阶段;计算了不同无因次井筒存储系数对流动阶段的影响,结果表明:随着无因次井底存储系数增加,流动第1、第2阶段被陆续掩盖;研究了裂缝干扰对产量的影响。研究表明:位于水平段跟、指端部分的裂缝较位于中间部位的裂缝产量高,裂缝产量沿水平段分布呈"U"型。

An Analysis of Unsteady Pressure of Fractured Horizontal Wells in Tight Gas Reservoir

By employing the discrete crack model ,considering the crack as thevariable mass flow , using the superposition principle , the calculation of pressure drop of any point in the gas reservoircan be worked out .Through coupling the gas flow inthe fracture surface as well as the cracks in the reservoir ,the transient pressure analysis model of fracturedhorizontal wells in tight gas reservoirhas been built up .Based on the analysis of the dimensionless pressure derivative of the physical meaning of the corresponding slope ,the unsteady flow process was divided into five stages:thelinear flowin cracks , the linear flow between cracks , the earlyradialflow in gas reservoir ,the linear flowin gas reservoir and the later radial flow in gas reservoir .The influence of different dimensionless wellbore storage coefficient on the flow stages is calculated .Results show that withthe increase of dimensionless bottom hole storage coefficient ,the flow of the first and second stage have been covered .T he effect of crack interference on yield is analyzed too .T he research indicates that the yield incracks in the horizontal section and the end part is higher than that in the middle part ,and the yield distributionof cracksalong the horizontal section emerges as a“U” shape .