Research and application of rock physics modeling for shallow gas reservoirs in South China Sea

Abstract The shallow gas-bearing formations in the South China Sea present distinctive petrophysical challenges due to their poorly consolidated lithology and early diagenetic characteristics. This research synthesizes several fundamental rock physics theories to establish an integrated workflow for characterizing gas-bearing formations in the offshore shallow sedimentary basins of the South China Sea. The paper evaluates the modulus of elasticity of the rock matrix via Voigt–Reuss–Hill averaging, addressing the polymineralic nature of reservoir lithologies. The Hashin–Shtrikman theory is applied to derive the modulus of elasticity of the dry frame at different porosities while applying the Hertz–Mindlin model to compute the elastic modulus under critical porosity. This study applies the patchy saturation theory combined with the Gassmann fluid substitution equation to analyze the variations in the elastic parameters of rocks under fluid-saturated conditions. Validation against logging datasets confirms the model's capability to universally characterize shallow gas reservoirs across different geological settings in the study area. This generalized workflow establishes essential theoretical foundations for quantitative seismic interpretation of shallow gas-bearing formations in the South China Sea.