Saturation Model of Shaly Sand Based on Effective Medium Theory

The saturation model of shaly sand is fundamental to the evaluation and development of oil and gas reservoirs, as its accuracy directly impacts the precision of reservoir parameter calculations. Traditional saturation models often neglect the significant influence of pore structure on rock conductivity, leading to notable limitations in practical applications. To address these limitations, a novel saturation model specifically designed for shaly sandstone was developed, grounded in the effective medium theory. The model divides shaly sand into wet clay particles, oil pores, water pores, and non-conductive particles, and derives the saturation model using effective medium theory. The influence of pore structure on conductivity is incorporated through the parameters of percolation rate and percolation exponent. Unlike conventional approaches, such as the Simandoux model, which primarily account for clay content while disregarding pore structure, the proposed model offers a more comprehensive representation. The model was systematically validated by comparing its results with saturation data from a sealed core well, enabling a comprehensive evaluation of its perfomance relative to traditional models such as the Simandoux and Archie models. The newly developed model demonstrated superior accuracy compared to traditional models. Specifically, the average absolute error of the effective medium theory-based model was only 4.7% when compared to core analysis results, significantly outperforming the Simandoux and Archie models. This improvement is attributed to the model's ability to comprehensively account for both clay content and pore structure characteristics, which are often neglected in conventional approaches. This innovation overcomes the limitations of traditional models and enhances the accuracy of reservoir parameter calculations. The findings hold significant practical implications for improving reservoir characterization and development strategies in shaly sand reservoirs.