Theoretical Study on Rock-Electric Characteristics of Complex Shaly Sandstones and its Application to Reservoir Saturation Evaluation

The conductive model of complex shaly sandstones is used to describe the rock-electric characteristics, which is the key to reservoir saturation evaluation. At present, conductive models as a single factor are unable to accurately reflect the conductive property of complex shaly sandstones, which limits the evaluation precision of reservoir saturation. In this paper, by incorporating multiple factors of shale, pore structure, and conductive structure, a novel modified equivalent rock element model (MEREM) is developed to analyze the rock-electric characteristics and calculate the reservoir saturation in complex shaly sandstones. Our studies show that pore structure and shale significantly influence the conductive property of complex shaly sandstones. However, they have the opposite effect and may cancel out each other. Moreover, the conductive model presented here has achieved promising results in interpreting experimental data. Furthermore, the MEREM is extended to oil-bearing shaly sandstones, demonstrating that the rock resistivity at different saturation is sensitive to pore structure and shale. The MEREM is applied to predict the reservoir saturation, and the computed saturation is found to be well-matched with cores. Therefore, the proposed MEREM is good for interpreting rock-electric characteristics and the evaluation of reservoir saturation in complex shaly sandstones.