Shapley-Value Weighted Rock Physics Application for Quantifying the Fraction of Morphologies in Gas Hydrate-Bearing Formations

Gas hydrate deposits exhibit diverse morphologies, including matrix-supporting or load-bearing, cementing, fracture-filling, and pore-floating types. Heterogeneity brought in by the mix of hydrate morphologies can perturb the effective stress state on the formation due to the varied responses in the pore pressure of the formation. These morphologies significantly influence hydrate saturation estimation and formation geomechanics, making accurate characterization crucial for assessing the formation stability and potential greenhouse gas release. This study investigates gas hydrate saturation potential in the Indian offshore, delineating morphology types and associated formation instability. We developed a consolidated forward-inverse model incorporating rock physics theories tailored to Indian hydrate-bearing formations. This model computes the elastic response of gas-hydrate-bearing sediments across four fundamental hydrate morphologies (and their corresponding bounds). A Bayesian-optimized forward-feed Gaussian Process was employed for the inverse mapping of hydrate saturation using observed compressional velocity data. Additionally, a novel Shapley-value analysis was utilized for the statistical segmentation and mixing of morphologies. Results revealed dominant morphologies at two sites: NGHP-02–022C showed fracture-filling (42%), pore-floating (33%), and load-bearing (25%) types, while NGHP-02–23C exhibited cementing (57%) and load-bearing (43%) morphologies. The proposed method’s validity was confirmed through comparison with previous pressured-core studies. This research enhances our understanding of the hydrate morphology distribution in Indian offshore formations, providing valuable insights for accurate saturation estimation and geomechanical stability assessment. The findings contribute to improved characterization of gas hydrate deposits and their potential impact on the formation stability.