The Characteristics and Parameter Correlation of Pore–Throat Structure in Ultradeep Carbonate Gas Reservoir Based on Dual-Resolution Computed Tomography Scanning

Abstract

The pore–throat structure characteristics of the reservoir are key factors limiting the efficient development of ultradeep carbonate gas reservoirs. This study uses casting thin section experiments, dual-resolution computed tomography (CT) scanning, and digital-core reconstruction technology to study the characteristics and parameter correlation of pore–throat in ultradeep carbonate gas reservoir. The dual-resolution CT scanning experiment further quantitatively reveals that the cumulative volume of mesopores and macropores in ultradeep carbonate rocks accounts for 43.53%; it cannot be ignored. The sample size of low-resolution CT scanning is large, making it suitable for studying the spatial distribution and heterogeneity of multiple pore types. However, its microscopic pore parameters are less effective for correlation studies with the porosity and permeability. High-resolution CT scanning has a high recognition accuracy and has great advantages in the identification of micropores and fractures. It can significantly improve the accuracy of microscopic pore parameters such as porosity, pore number, equivalent diameter of pore, equivalent diameter of throat, tortuosity, and shape factor in the CT pore model. In the correlation study, these microscopic parameters show a good correlation with porosity and permeability, except for the coordination number. In addition, this study focuses on revealing that the two-dimensional (2D) fractal dimension and the geometric standard deviation method based on the volume fracture of 2D show good correlation with porosity and permeability, proving that the two newly introduced parameters are helpful for characterizing the porosity and permeability. The research results offer a reference for researchers in selecting CT scanning resolution and comprehending the characteristics of ultradeep pore–throat structures.