基于网格分析法的页岩储层等效孔隙纵横比反演

Inversion of effective pore aspect ratio for shale reservoir using grid search method

页岩储层通常具有复杂的孔隙空间,等效孔隙纵横比作为描述储层孔隙空间的重要参数,对地层的弹性波速度影响显著。因此,准确预测储层的等效孔隙纵横比对页岩储层建模及横波预测具有重要意义。为了分析页岩储层的等效孔隙纵横比,提出了一种自洽模型与网格分析法相结合的孔隙纵横比反演方法。自洽模型可以利用孔隙纵横比、矿物体积百分比等物性信息来模拟弹性波速度等弹性信息。网格分析法通过将测井值正态分布展开来模拟测量误差,从而降低由测量误差导致的反演不确定性,最终反演得到可靠的孔隙纵横比概率密度分布。通过对北美Barnett页岩储层的实际应用,结果表明,该方法与常规方法相比,其反演结果更加稳定,同时,利用该反演结果还可预测得到较为准确的横波速度。

The pore spaces of shale reservoir are usually complicated. Effective pore aspect ratio is a significant parameter to characterize pore spaces of formations, which obviously impact the elastic velocities of formations. Therefore, the accurate es- timation of effective pore aspect ratio for shale reservoir is meaningful in rock physics modeling and S-wave velocity predic- tion. In order to estimate the pore structure of tight formation, a workflow is proposed for pore aspect ratio inversion by com- bining self-consistent approximation （SCA） method and grid search method. Elastic properties of formation can be estimated by inputting physical parameters, such as pore aspect ratio and mineral concentration, to SCA model. Grid research method can reduce the uncertainty during the inversion of pore aspect ratio by normally distributing the logging data. The combina- tion of two methods can enhance the stability of inversion results. The workflow is performed to the Barnett shale reservoir in North America, and the results provide us a robust prediction of pore aspect ratio. Finally, the S-wave velocity can be predic- ted accurately by using the inverted pore aspect ratio.