川东北地区碳酸盐岩储层孔隙度预测方法研究

摘要

许多研究都已经证实在碳酸盐岩储层中孔隙结构对声波速度影响很大,因此在孔隙度反演时必须考虑孔隙结构的影响.通过对Gassmann方程的合理简化并引入Eshelby-Walsh干燥岩石椭球包体近似公式;导出了计算岩石孔隙结构参数的公式,并统计分析出岩石孔隙结构与其它弹性参数间的变化规律.利用这种统计规律推出了考虑碳酸盐岩孔隙结构孔隙度计算公式.由于该式计算孔隙度时考虑了纵波速度、横波速度、密度、岩石孔隙结构参数的影响,使求取孔隙度更加合理.最后测井数据试算结果与川东北地区应用实例都证实利用该方法预测碳酸盐岩孔隙度精度高于常规方法.%Many studies have been confirmed pore structure has a great influence on acoustic velocity in a carbonate reservoir. Therefore, the porosity inversion must take into account the influence of pore structure. A simplified Gassmann equation is derived firstly by using a reasonable assumption in which the compressive coefficient of the saturated pore fluid is much greater than the rock matrix and utilize the Eshelby-Walsh relation to replace the equivalent modulus of dry rock in the Gassmann equation. On this basis, the formula for calculating the parameters of rock pore structure are derived and the variation law between the pores of the rock structure and other elastic parameters are analyzed; a new formula for porosity calculation is derived to take into account the pore structure of carbonate rocks by use of this statistical law. This new formula allows the porosity calculation more reasonable because it consider the compressional wave velocity, shear velocity, density, rock porosity structure parameters. At the last, the practical log and seismic data calculation proves that the accuracy of a new approach to predict the porosity based on the pore structure of carbonate is higher than the conventional method.