砂岩-页岩互层气藏物质平衡方程构建与应用

在国内外很多盆地的气藏,富含有机质的页岩中发育不连续的砂岩夹层,页岩气层和砂岩气层具有很好的连通性,同属于一个压力系统。在这种类型的页岩气藏的储量计算中,不应该忽略砂岩中的游离气储量。为了计算地质储量,首先分析了页岩和砂岩的骨架、孔隙及其流体储存的差异性,在此基础上,将气藏的储集单元分为无机质基质和有机质基质两大类,并建立了此类页岩气藏的体积模型。根据体积守恒原理、Langmuir等温吸附模型和PalmerMansoori模型,分别讨论了两类基质在地层压力下降过程中孔隙和流体的变化特征,推导出页岩-砂岩互层气藏的物质平衡方程。通过实例分析验证了新的物质平衡方程能够分别计算出页岩与砂岩中的游离气储量和吸附气储量,以及开发过程中解吸的天然气体积。

Application and derivation of material balance equation for shale gas reservoirs with laminated sandstone pay zones

In many basins with the thin laminated groups of sands imbedded in organic-rich shale,shale and sandstone pay zones communicate with each other,and should be taken as inseparable parts of one pressure system.In order to calculate the original gas reserves in place,the differences of pores and fluid between shale and sandstone were compared,and the reservoir was divided into inorganic matrix and organic matrix,on which the volume model was established.According to the principle of material balance,the Langmuir adsorption isotherm model and Palmer & Mansoori model,the change of porosity and fluid with pressure drop in both matrices were discussed,and the material balance equation for reservoir with shale gas and laminated sandstone pay zones was derived herein.The field case study proves that new material balance equation can be applied to calculate original free gas and adsorbed gas reserves in shale or sandstone,and estimate the desorbed gas in development process.