一种体现孔隙形态影响的四参数孔隙度反演方法

Four parameters porosity inversion method representing the effect of pore morphology

传统的测井孔隙度反演方法在反演复杂孔隙形态地层的孔隙度时往往存在偏差。孔隙形态的影响可以利用等效介质模型体现,提出了一种四参数孔隙度反演方法,即,引入差分等效介质(Differential Effective Medium,DEM)模型,将孔隙度反演与孔隙形态的影响相结合,利用中子、密度、纵波时差和横波时差四个参数实现地层的孔隙度和孔隙纵横比的同步反演。首先利用中子、密度和纵波时差反演地层孔隙度初值,通过DEM模型求取孔隙纵横比初值;而后利用纵波速度、横波速度和体积密度信息同步反演声学孔隙度和孔隙纵横比;最后综合利用中子、密度、纵波速度和横波速度数据,对地层孔隙度和孔隙纵横比进行同步反演。以西南某探区深层白云岩地层孔隙度反演为例,比较了不同孔隙度反演方法的效果,验证了四参数孔隙度反演方法的有效性。

The deviations arise when inverting the porosity of reservoirs in complex pore structure with conventional porosity inversion methods.The effect of pore morphology on acoustic velocity can be indicated quantitatively by means of the equivalent media model.S-wave velocity is introduced to improve porosity equation and to calculate the effects of porosity and pore aspect ratio.The porosity and pore aspect ratio are simultaneously inverted using the density,neutron porosity,acoustic velocity and S-wave velocity data to improve inversion accuracy.Firstly,the initial porosity is inverted with neutron porosity,density and acoustic velocity,and the initial pore aspect ratio is calculated by difference equivalent model（DEM）.Then,the acoustic porosity and pore aspect ratio are inverted simultaneously with bulk density and velocities information.Finally,the formation porosity and pore aspect ratio are inverted simultaneously with the comprehensive utilization of neutron porosity,Swave velocity,acoustic velocity and bulk density.This method is applied to invert the porosity of deep dolomite formation in somewhere southwest of China.By comparing the results with other methods,the validity of this four parameter porosity inversion method is proved.