Quantitative Characterization of Pore-invasive Gas Hydrate Morphology via Rock Physics Modeling

Advancing rock physics modeling is critical for understanding the physical properties of gas hydrate-bearing sediments and assessing hydrate reservoirs. This study presents a combined elastic and electrical rock physics framework to quantitatively characterize the morphology and distribution of pore-invasive gas hydrates, a dominant reservoir type in marine and permafrost environments. Elastic modeling, grounded in granular medium contact theory and Gassmann’s equation, reveals the influence of hydrate saturation and initial porosity on P- and S-wave velocities. However, these velocities alone are insufficient to uniquely constrain hydrate morphology. To overcome this limitation, we refined Archie's law by introducing an empirical ion concentration exponent, improving the sensitivity of electrical conductivity models to hydrate distributions within pores. By coupling these models, we simulate hydrate formation processes and evaluate their impact on seismic and resistivity properties. Our results highlight several key conclusions. First, experimental observations suggest that a uniform distribution of hydrates within the pore framework is most consistent with measured geophysical responses, despite the potential for ring-shaped saturation patterns during laboratory experiments. Second, we identify a distinct morphological evolution during hydrate growth: hydrate structures transition from grain-supporting to contact-cementing and finally to pore-filling morphologies as saturation increases. This progression is reflected in both velocity and resistivity trends, offering complementary insights into the hydrate formation process. This work not only advances the understanding of hydrate formation but also provides a robust framework for evaluating hydrate reservoirs, contributing to efforts in energy resource development and environmental management.