修正岩石压缩系数的页岩气藏物质平衡方程及储量计算

由于页岩气藏孔隙度变化与常规气藏孔隙度变化不一样,受有效应力和基质收缩的耦合作用,前者使孔隙度减小,后者使孔隙度增加,因此建立页岩气藏物质平衡方程时必须考虑二者的综合作用。从物质平衡原理出发,运用Bangham固体变形理论、Langmuir等温吸附模型,推导出了修正岩石压缩系数的页岩气藏物质平衡方程,并对方程线性化,得到只含有原始游离气和原始吸附气的直线方程。代入实际生产数据,求得关于线性方程的数据点,并对数据点线性拟合,其拟合方程的斜率是原始游离气的含量,截距是原始吸附气的含量,两者相加求得页岩气藏的原始地质储量。实例分析表明,考虑基质收缩效应,使得页岩压缩系数前期不断减小,后期趋于稳定;由于压缩系数的改变,使得页岩气藏储层孔隙度的变化比常规气藏缓慢;通过对页岩气藏岩石压缩系数的修正以及实际生产数据点的线性拟合,求得页岩气藏中吸附气的含量增加,游离气的含量减少,页岩气藏总地质储量增大,且与实际储量更加接近。

Material balance equation with revised rock compressibility for shale gas reserve calculation

As shale gas reservoirs have different change pattern of porosity with conventional gas reservoirs and their effective stress tending to lower porosity and matrix shrinkage tending to enlarge porosity have coupling effect,these two factors must be considered comprehensively when establishing the material balance equation for shale gas reservoir.Based on the material balance principle,Bangham solid deformation theory and Langmuir isotherm adsorption model are used to establish shale gas reservoir material balance equation with correction rock compressibility.The equation is linearized to a straight line equation only containing original free gas and absorbed gas.Actual production data are substituted in the equation to obtain the data points of the linear equation.These data points are fitted to obtain a fitting equation,the slop of which is the content of free gas and theintercept is original absorption content of gas.The sum of these two is original geological reserves of shale gas reservoir.Case analysis shows that considering the matrix shrinkage effect makes compressibility factor decrease at the beginning and stablize at the later.The lowering of shale gas reservoir porosity caused by the change of compressibility factor is slower than that of conventional gas reservoir.The correction of the rock compressibility of shale gas reservoirs and linear fitting the actual production data lead to the increase of the calculated amount of absorbed gas and the decrease of estimated content of free gas,so the estimated geological reserves increase and are more close to actual reserves.