基于碳酸盐岩孔隙结构预测孔隙度方法研究

Method for predicting the porosity based on the pore structure of carbonate

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.本文通过对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,推导出包含岩石孔隙结构参数、饱和岩石压缩系数与岩石基质压缩系数三个参数的计算孔隙度的新公式,该式岩石基质压缩系数是通过Russell流体因子和Gassmann-Boit-Geertsma方程计算式建立目标函数反演获得的,然后通过测井交汇图技术把岩石孔隙结构参数与岩石基质压缩系数优选转换成纵横波速度与密度关系式,进而导出具体地区考虑碳酸盐岩孔隙结构孔隙度具体计算公式,测井与地震资料应用表明,基于碳酸盐岩孔隙结构的孔隙度预测方法的精度高于常规方法.

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. In this paper, we first derive a simplified Gassmann equation 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, we derive a new formula of the three parameters for porosity calculation to take into account the rock pore structure parameters, saturated rock compressibility coefficient and rock matrix compression coefficient. The rock matrix compression coefficient in the formula is iverted by combining the Russell fluid factor with the Gassman-Biot-Geertsma equation. Rock pore structure parameters and the rock matrix compression coefficient in the formula are preferably converted to P. S- wave velocities and density relational expression by logging cross plot technology. Predicting the porosity for specific areas based on the pore structure of carbonate is derived. At the last, the practical data 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.