基于CT扫描的低渗砂岩分形特征及孔渗参数预测

Fractal characteristic of low-permeability sandstone and physical parameters prediction based on CT scanning

 曹廷宽 2 刘成川² 曾焱² 卜淘²

中国石化西南油气分公司博士后科研工作站，四川 成都 610041 中国石化西南油气分公司勘探开发研究院，四川 成都 610041）

 低渗砂岩孔喉狭小，结构复杂，难以进行岩石孔隙定量表征及物性参数的准确预测。为此，文中结合数字岩心技术及分形理论，提出了具有针对性的解决方法——选取四川盆地某气藏具有代表性的低渗砂岩岩样进行CT扫描，构建低渗砂岩微观结构图像和三维数字岩心，利用计盒维数方法分析低渗砂岩岩心孔隙空间的分形维数特征。结果表明：低渗砂岩孔隙空间具有良好的分形特征，利用分形理论可以描述其复杂的孔隙结构特征；通过建立岩石孔隙度、渗透率与孔隙空间分形维数的关系式，可有效预测该类低渗砂岩的孔渗参数，拓宽了分形理论在低渗储层物性评价中的应用范围。

 For narrow pore-throat and complex structure of low-permeability sandstone, the qualitative description of pore space and physical parameters prediction are very difficult. Combining the technology of digital rock and fractal theory, the corresponding solution is proposed in this paper. CT scanning was applied to study the samples obtained from a gas reserve in Sichuan Basin, and structural images as well as three dimensional digital rocks were reconstructed. Then, the box-counting approach was used to analyze the fractal dimension characteristic of void space in digital rock models. Result shows that low-permeability sandstone is of fractal porous media, and the fractal theory is capable to analyze the complex pore structure of it. The good correlations revealed between the pore fractal dimensions and porosity or permeability can be used to predict the rock physical parameters accurately. Thus the presented method can extend the application range of the fractal theory in evaluating physical parameters of low-permeability reserves.

10.6056/dkyqt201705013