Pre‐Stack Seismic Inversion of Dual‐Porosity Geometry in Deep Coalbed Methane Reservoirs Based on Decoupled Equivalent Medium Theory

ABSTRACT Seismic inversion quantitatively extracts reservoir properties from seismic data, which has gained increasing attention in assisting the exploration and evaluation of deep coalbed methane (DCBM) reservoirs. However, the accuracy of seismic prediction is limited because the DCBM reservoirs exhibit complex pore geometries governed by a dual‐porosity system. To address this limitation, the study presents a dual‐porosity parameter seismic inversion method based on decoupled equivalent medium theory. A dual‐porosity rock physics model is constructed and then decoupled to derive a linear forward operator that links matrix porosity, crack porosity and crack aspect ratio to the corresponding elastic parameters. To account for lithological variability, a Gaussian mixture model is employed to describe the joint prior probability distribution of dual‐porosity parameters. Well‐log data are applied to invert matrix porosity, crack porosity and crack aspect ratio, which serve as prior constraints in the iterative Bayesian inversion framework, thereby enhancing the stability and accuracy of the forward operator. By explicitly treating dual‐porosity parameters as inversion targets, the proposed method effectively captures the spatial heterogeneity of pore geometries in DCBM reservoirs. Borehole‐side synthetic seismic gather validation results demonstrate that the proposed approach significantly enhances inversion accuracy compared with conventional equivalent‐porosity inversion methods. The application to pre‐stack seismic data demonstrates the ability of the method to capture the dual‐porosity geometry.