Application of Digital Core Analysis Technology to Study Filtration-Capacity Properties and Structure of Highly Permeable Rocks of Underground Gas Storage Facilities

The paper presents the results of pore space studies of highly porous reservoir rocks of underground gas storage (UGS) facilities using the digital analysis of computed microtomography images. The methodology of complex nondestructive analysis of structural and filtration-capacitance properties has been developed. Structural heterogeneities and rock fracturing were evaluated. 3D-models of specimen inner space were created on the basis of multi-scale images. The values of open and closed porosity, geodesic tortuosity were calculated, the characteristics of percolation paths in the studied rocks were analyzed for different directions of intrusion. Conclusions were made about the homogeneity of percolation path distribution over the rock volume. The spatial distribution of porosity in the rocks was studied, and porometry analysis of the rocks was carried out. Numerical modeling of filtration processes on the obtained structures in the framework of Stokes approximation for three selected directions in the rock by means of GeoDict software was carried out. It is shown that there is no pronounced dependence of changes in filtration properties in the selected directions on the quantitative characteristics of the pore space. The conclusion is made about the degree of anisotropy of filtration-capacitance properties of rocks. The good correspondence of the characteristics measured in the course of digital analysis with in-situ data and experimentally obtained laboratory values is shown. The described technique allows to simplify data acquisition on the characteristics of fine-grained reservoir rocks, and is designed to extend the approaches to nondestructive analysis of core material. Combined application of the proposed methodology of digital analysis of low-strength reservoirs and laboratory geomechanical core testing is one of the stages in the development of a comprehensive approach to determining the parameters of safe operation of gas wells and reducing the risks of sanding in fields with weakly cemented reservoirs.