Innovations and Practices in SEC Reserve Evaluation Methods for High-Pressure/Abnormally High-Pressure Fractured Sandstone Gas Reservoirs

With global oil and gas exploration advancing into deep and complex reservoirs, high-pressure and abnormally high-pressure fractured sandstone gas reservoirs have emerged as critical reserves growth targets. However, their heterogeneous flow characteristics, complex high-pressure phase behavior, and staged development processes pose challenges for SEC reserves estimation using conventional methods (volumetric, decline curve analysis, and material balance methods), including strong parameter multiplicity and significant dynamic fitting errors. To address the evaluation needs of ultra-deep fractured sandstone gas reservoirs in the Tarim Oilfield, this study establishes a tripartite framework integrating “theoretical analysis, methodological innovation, and case validation.” By incorporating flow characteristics across development stages (early production testing, mid-term stable production, and late decline), a stage-specific evaluation model is developed. Applied to a high-pressure/abnormally high-pressure fractured sandstone gas reservoir in the Tarim Oilfield, the results demonstrate: Early stage: Fractal theory is introduced to revise fractal porosity and threshold pressure gradient, reducing porosity and gas-bearing area errors by \(10\%\) . Mid-term: A modified CKB model optimizes high-pressure phase behavior calculations, lowering water invasion error and improving reserves accuracy by \(10.7\%\) . Late stage: A fracture closure coefficient is employed to characterize dynamic permeability attenuation, refining the decline model and enhancing reserves accuracy by \(9.9\%\) . The innovative approach achieving less than \(10\%\) error compared to numerical simulations meeting the SEC's “reasonable certainty” criteria. The proposed stage-specific evaluation system overcomes the homogeneity assumptions and static parameter limitations of traditional methods. It establishes a multi-dimensional coupling model integrating “geological static parameters, dynamic development characteristics, and highpressure phase behavior effects,” offering a reference methodology for SEC reserves assessment of similar reservoirs. This advancement holds significant value for precise asset quantification in deep hydrocarbon reservoirs.