Dielectric properties of fractured reservoir sandstones based on digital rock physics technique

Understanding the dielectric properties of reservoir rocks has significant applications in all aspects of the petroleum industry. Small-scale fractures are one of the geological factors that affect the dielectric properties of rocks. Obtaining the quantitative relationship of the influence of fractures on the dielectric properties of fractured rocks has important theoretical and practical significance. Based on the three-dimensional microscopic digital structure of artificial sandstone with fractures, the validity of the numerical calculation method is verified by comparing the dielectric properties of the rock calculated based on the three-dimensional finite-difference algorithm with the experimental data. The dielectric properties of the matrix (i. e., the rock without fractures) with various porosities are then determined using the multiphase incremental model, the validity of which is tested using the measured results of the unfractured sample. Finally, fractures with varying crack density and aspect ratio are artificially added into the CT structure of the matrix to form new fractured rocks, and their dielectric properties are simulated using the validated three-dimensional finite-difference model. The results show that the influences of fractures on the dielectric properties of the sandstone increase with the decrease of porosity of the sandstone matrix, and the dielectric properties of the fractured sandstone are positively correlated with fracture density and fracture aspect ratio when fracture porosity changes with fracture density or fracture aspect ratio. However, the dielectric properties of the fractured sandstone increase with the decrease of fracture aspect ratio as fracture porosity unchanged. The variation of the fractures impacts the dielectric properties of the fractured rocks with varying matrix porosity in a similar trend, but the amount of the impact increases with decreasing matrix porosity. The research results of the influence of fracture parameters and matrix porosity on the dielectric properties of fractured sandstones provide a basis for the quantitative characterization of fractured oil and gas reservoirs based on dielectric properties, and have important application prospects in oil and gas exploration and development.