新型页岩气藏物质平衡方程

页岩气主要以吸附气的形式吸附在基质微孔隙表面,以游离气的形式存在于基质孔隙和裂缝孔隙中,不考虑基质、裂缝双重孔隙介质的页岩气藏物质平衡方程不能准确地计算储量。文中从质量守恒的角度建立了同时考虑吸附相密度、吸附相视孔隙度、吸附气解吸对固相变形的影响,以及基质和裂缝孔隙体积随压力变化的新型物质平衡方程。通过实例计算可知:游离气主要存在于裂缝孔隙中,吸附气储量占据总储量的52.15%,基质中游离气储量、裂缝中游离气储量、基质中吸附气的储量的计算结果与基质孔隙度、裂缝压缩系数和吸附相密度密切相关。因此,在进行储量计算时需要考虑基质和裂缝双重孔隙介质,并应加强对基质孔隙度、裂缝压缩系数和吸附相密度的研究,以获取更加准确的参数。

New material balance equation for shale gas reservoir

The adsorbed gas adsorbs on the substrate surface and the free gas stores in the matrix and fracture porosity.However most predecessors do not consider the dual porosity system and adsorbed phase visible porosity when the material balance equation is derived,which cannot calculate shale gas reserves truly and accurately.So a new material balance equation is established,considering such factors as adsorbed phase visible porosity,matrix and fracture porosity changing with pressure,adsorbed gas density,and effect of gas adsorption and desorption of the solid phase deformation.Numerical examples shows that free gas mainly stores in the matrix and fracture porosity,adsorbed gas reserves account for 52.15％ of total reserves;and the free gas reserves in matrix and the free gas reserves in cracks are very sensitive to matrix porosity,crack compress coefficient and adsorbed phase density.It can be seen that the free gas mainly exists in fracture pore.In order to obtain more accurate parameters,the research on the matrix porosity,cracks compressibility and density of the adsorbed phase should be increased.