考虑启动压力梯度的页岩气藏数值模拟

页岩气作为一种重要的非常规能源,其渗流及开发原理越来越受到关注。在页岩气井开采过程中,为了全面认识井底压力的响应特征及影响因素,根据页岩气渗流机理、吸附气解吸特征、渗流理论和质量守恒定理,建立双孔介质页岩气藏数学模型。模型以启动压力梯度和等温吸附的原理为前提,应用有限差分法,得到数值模型,编制相应程序对数值模型求解,分析了启动压力梯度、几何因子、储容比、Langmuir压力、Langmuir体积对气井井底压力变化的影响。结果表明:双重介质模型能够准确描述吸附气在储层中的解吸过程、基质系统和裂缝系统之间的窜流过程;考虑启动压力梯度更加接近实际地层;考虑吸附解吸作用使井底压力缓慢降低,探测地层边界较晚;利用地层参数分析及室内实验可以间接求出页岩气藏解吸附过程中Langmuir压力和Langmuir体积,这对气井井底压力分析和产能预测非常重要。

Numerical Simulation of Shale Gas Reservoir Considering Startup Pressure Gradient

Shale gas is a very important unconventional energy and its seepage principle and development have obtained more and more attention.Established is a mathematical model for double porosity medium shale gas reservoir according to shale gas seepage mechanism,gas adsorption and desorption characteristics,seepage theory and principle of conservation of mass.Based on start-up pressure gradient and isothermal adsorption principles,finite difference method is applied to obtain a numerical model.Prepared is a corresponding program to solve the numerical model.Analyzed are effects of the start-up pressure gradient,geometrical factors,reserve/volume ratio,Langmuir pressure and Langmuir volume on bottom hole pressure changes.The results show that the dual medium model can accurately describe the desorption process of the adsorbed gas in reservoir stratum,fluid channeling process between matrix system and crack system.Formation parameters analysis and indoor experiments can be used to obtain indirectly Langmuir pressure and Langmuir volume in shale gas reservoir desorption process,which is very important to bottom hole pressure analysis and productivity prediction.