A unified rock physics model for carbonate reservoir characterization: Transport and elastic properties

Rock physics models provide an understanding of the complex interrelationships among physical properties, mineral composition, fluid type, and microstructural characteristics of rocks. While these models are commonly used to estimate the elastic and electrical properties of rocks, their application to thermal properties has been limited due to a lack of reliable experimental data. This study aims to develop a rock physics model to simulate the thermal, electrical, and elastic properties of carbonate reservoirs. Based on measurements of thermal conductivity, electrical resistivity, and elastic wave velocities from 34 homogeneous carbonate core plugs from the Timan-Pechora Basin, saturated with various pore fluids, including gas, brine (6, 60, and 180 g/L), and kerosene (as an oil proxy), a unified rock physics model for simulating these transport and elastic properties is developed. The model utilizes a generalized singular approximation scheme based on effective medium theory, using unified microstructural parameters. These parameters are derived from the measurements of a selected physical property and are used to estimate other properties. Different input datasets are discussed to determine microstructural parameters and, therefore, to evaluate one physical property against another. The proposed model estimates all mentioned properties of carbonate samples saturated with various pore fluids, achieving mean absolute percentage errors of 4% for thermal conductivity and 8% for elastic wave velocities (calculated vs. measured). For electrical resistivity, the mean absolute logarithmic discrepancy is 0.15 decades across tested brine salinities. Additionally, the study reports simulation results for carbonate thermal conductivity to examine the effects of pore fluids (gas, brine, oil, and their mixtures) and void space geometry. The developed model is applied to interpret variations in the physical properties of another carbonate reservoir in the same basin, and its limitations are discussed. • A unified rock physics model integrates the transport and elastic properties of carbonates • The integration is achieved by using unified microstructure parameters • The model encompasses multiple rock physical properties for various saturation states • The model is successfully utilized for experimental data of a similar carbonate reservoir