Synergistic elastic and electrical modeling for quantitative analysis of gas hydrate formation evolution in pores

ABSTRACT Pore-invasive gas hydrates represent a dominant reservoir type that has garnered increasing global attention. However, the current understanding of their formation and evolution in sediments remains superficial, impeding efforts toward recovery assessment. In contrast to predominantly qualitative approaches found in the current literature, a novel method for a more quantitative understanding of this dynamic process is developed. Leveraging granular medium contact theory and Gassmann’s equation, we develop an elastic model that accounts for hydrate pore morphologies within sediment pores. Our elastic model calculations unveil the significant impact of initial porosity and hydrate saturation on P- and S-wave velocities, highlighting the nonuniqueness of discriminating hydrate morphology based on these velocities alone. To address the variability in hydrate electrical properties, we refine Archie’s law by introducing an empirical parameter, the ion concentration exponent, which better accounts for the distribution of hydrates and the associated effect on the conductivity of pores. Although our experimental method may lead to a ring-shaped distribution of hydrate saturation within the sample, the modeling results suggest that a uniform distribution of hydrates within the pore framework is more plausible than experimental measurements. Recognizing the shortcomings of prevalent models, we develop an innovative elastic inversion approach that simulates the hydrate accumulation process, reflecting the progressive solidification impact of increasing hydrate saturation. Using a synergistic elastic and electrical rock-physics framework, we analyze experimental geophysical data to trace the hydrate formation trajectory. Our interpretations illustrate an initial dominance of grain-supporting hydrates, transitioning to contact-cementing and pore-filling morphologies at advanced saturation levels. These joint models provide valuable insights into the quantitative assessment of gas hydrate reservoirs, offering a comprehensive understanding of the intricate interplay between elastic and electrical properties during hydrate growth.