考虑启动压力梯度的煤层气羽状水平井开采数值模拟

建立了对非均质各向异性双重介质煤层气进行定向羽状水平井开采的数学模型.模型中考虑了与气体吸附、解吸和扩散相耦合的三维气、水两相渗流以及储层的压力敏感性和煤层本身所具有的低渗透特性,即低渗透地层启动压力梯度的影响,同时还考虑了井筒内的压降损失.利用有限差分法对数学模型进行了数值求解,完成了煤层气定向羽状水平井开采的数值模拟,并着重分析了启动压力梯度对模拟产量的影响.计算结果表明,利用定向羽状水平井能够大幅度提高低渗透煤层气的开采效率.启动压力梯度的存在会使煤层中羽状水平井的降压效果变差,从而减少煤层气的产量.

Numerical simulation of pinnate horizontal multilateral well for coal-bed gas development in consideration of start-up pressure gradient

A mathematical model for describing coal-bed gas recovery in heterogeneous anisotropic dual medium of pinnate horizontal multilateral wells was established. The factors including heterogeneity and anisotropy of stratum, sensitivity of permeability to pressure, friction and acceleration loss in wellbore and start-up pressure gradient in low-permeability coal bed were considered in this model. The numerical simulation method was presented and used to simulate the production of coal-bed gas in the pinnate horizontal multilateral wells. The effect of start-up pressure gradient on the simulated gas production was analyzed. The result of simulation showed that the gas production in low-permeability coal bed could increase greatly by drilling pinnate horizontal multilateral wells. The existence of start-up pressure gradient can make depressurization effect of pinnate horizontal multilateral well get worse, which promotes gas production reduced.