煤岩孔隙结构3D建模与孔隙度计算

Three-dimensional modeling and porosity calculation of coal rock pore structure

煤岩是一种双重孔隙介质,由基质孔隙和切割基质的裂隙组成,二者对流体的渗流和储集起着不同的作用,构建煤岩的微观孔隙结构对研究煤层气勘探开发中具有重要意义。在本研究中,我们使用煤岩数字岩芯和三维建模来研究煤岩的孔隙结构。首先利用煤岩2D薄片图像对其微观孔隙结构进行了定量分析,提取了煤岩孔隙和裂缝(割理)结构的定量信息,分析得到了实际煤岩薄片的面孔隙度以及孔隙半径的均值和标准差。使用二分法和基于压缩的球形随机堆积法确定孔隙数量。结合岩石物理分析结果,以非等径球体表示煤岩孔隙,得到了煤岩单重孔隙结构模型。随后,以纵横比远小于1的椭球表示煤岩中的裂缝(割理),进而得到了煤岩的双重孔隙结构模型。在此基础上,探究了不同孔隙纵横比与孔隙度之间的关系,得到了拟合关系式,结果表明两者之间存在非线性关系。此关系模型可为煤岩孔隙结构、孔隙结构参数预测和煤层气储层内部结构认识提供参考。

Coal rock is a type of dual-porosity medium,which is composed of matrix pores and fracture-cutting matrix.They play different roles in the seepage and storage capacity of coal rock.Therefore,constructing the micropore structure of coal rock is very important in the exploration and development of coalbed methane.In this study,we use a coal rock digital core and three-dimensional modeling to study the pore structure of coal rock.First,the micropore structure of coal rock is quantitatively analyzed using a two-dimensional thin-section image,and the quantitative information of the pore and fracture(cleat)structure in the coal rock is extracted.The mean value and standard deviation of the face porosity and pore radius are obtained using statistical analysis.The number of pores is determined using dichotomy and spherical random-packing methods based on compression.By combining with the results of the petrophysical analysis,the single-porosity structure model of the coal rock is obtained using a nonequal-diameter sphere to represent the pores of the coal rock.Then,an ellipsoid with an aspect ratio that is very much lesser than one is used to represent the fracture(cleat)in the coal rock,and a dual-pore structure model of the coal rock is obtained.On this basis,the relationship between the different pore aspect ratios and porosity is explored,and a fitting relationship is obtained.The results show that a nonlinear relationship exists between them.The relationship model can provide a basis for the prediction of coal rock pore structure and the pore structure parameters and provide a reference for understanding the internal structure of coalbed methane reservoirs.