具有越流的多层气藏的压力曲线特征

在多层油藏半透壁模型的基础上 ,建立了多层气藏的半透壁模型及其微分方程组 ,内边界条件考虑了表皮系数和井筒储集效应的影响 .利用有限差分方法编制了模拟试井程序 ,并与精确解进行了比较 .阐明了半透率、表皮系数、井筒储存对井底压力曲线、分层产量的影响 .随着半透率的增大 ,压力曲线越平缓 ,压力导数曲线的“凹陷”不断向外漂移 ;当各层表皮系数相同的时候 ,各层的井壁压力是相同的 ,各层产量趋于各自的产能系数 ;当各层的表皮系数不同时 ,各层的井壁压力是一组平行线 ,井底压力与井壁压力平行 ,各层产量不在趋于各自的产能系数 ;井筒储存可以减小层间越流的早期作用 .这些结果可用于多层气藏的不稳定试井分析

Pressure Behavior of the Stratified Gas Reservoir with Formation Crossflow

The semipermeable wall model of stratified gas reservoir and its differential equation were established based on the semipermeable wall model of stratified oil reservoir. The finite difference scheme of the differential equation and corresponding solving program are presented. In internal boundary conditions, skin factor and wellbore storage are considered. As an example, the numerical simulation result of a two layer gas reservoir is given. The numerical solutions of pressure and its derivative are compared with their analytic solutions, and there is little difference between them. The effects of semipermeability, skin factor and wellbore storage on bottom hole pressure curve and the output of every zone are stated: (1) the greater the semipermeability is, the evener the pressure curve is, and the "sag" of the pressure derivative curve moves toward right. (2) when the skin factors of all layers are the same, the wellbore pressures of them are also the same, and the output of every layer trends to itself productivity coefficient; when the skin factors of all layers are different, their wellbore pressure curves are a set of parallel curves, bottom hole pressure curve is also parallel to the set of parallel curves, and the output of every layer does not trend to itself productivity coefficient. (3) wellbore storage can decrease the early effect of interzonal cross flow. The research results in the paper can be used for the transient well testing analysis of stratified gas reservoir.