Investigation of the methane hydrate surface area during depressurization-induced dissociation in hydrate-bearing porous media

The surface area of hydrate during dissociation in porous media is essentially important for the kinetics of hydrate dissociation.In this study,the methane hydrate surface area was investigated by the comparison results of experiments and numerical simulations during hydrate decomposition in porous media.The experiments of methane hydrate depressurizationinduced dissociation were performed in a 1D high pressure cell filled with glass beads,an improved and valid 1D corescale numerical model was developed to simulate gas production.Two conceptual models for hydrate dissociation surface area were proposed based on the morphology of hydrate in porous media,which formed the functional form of the hydrate dissociation surface area with porosity,hydrate saturation and the average radius of sand sediment particles.With the establishment of numerical model for depressurizationinduced hydrate dissociation in porous media,the cumulative gas productions were modeling and compared with the experimental data at the different hydrate saturations.The results indicated that the proposed prediction equations are valid for the hydrate dissociation surface area,and the graincoating surface area model performs well at lower hydrate saturation for hydrate dissociation simulation,whereas at higher hydrate saturation,the hydrate dissociation simulation from the porefilling surface area model is more reasonable.Finally,the sensitivity analysis showed that the hydrate dissociation surface area has a significant impact on the cumulative gas production.

A comprehensive analysis of formation conditions,intrinsic properties,and mechanical responses of gas hydrate-bearing sediments

Natural gas hydrates(NGH)stored in submarine deposits are a promising energy resource,Yet,the deterioration in sediment strength can trigger geological disasters due to drilling-induced hydrate dissociation.Hence,an in-depth investigation on geo physical-mechanical performance of gas hydrate-bearing sediments(GHBS)is crucial for recovery hydrates safely and efficiently.This paper provides a comprehensive assessment of the research progress on formation conditions,intrinsic properties,and mechanical responses of GHBS.The key findings have been presented:gas composition,inhibitors and promoters alter hydrate formation by modifying the thermodynamic equilibrium of temperature and pressure.Also,we identified the key determinants of porosity of GHBS and revealed the correlation between permeability,hydrate saturation,and hydrate morphology.Moreover,we highlighted the differences in mechanical behavior between hydrate-free sediments and GHBS along with their underlying mechanisms.Furthermore,we examined the methods for GHBS preparation as well as the employed test apparatuses,providing critical insights into the limitations and recommendations.By synthe-sizing data from existing literature,we conducted a comprehensive analysis of the dependence of mechanical parameters of GHBS on factors such as hydrate saturation,effective confining stress,and temperature,and dis-cussed the mechanical responses subjected to various hydrate dissociation methods.Finally,we offer a perspective for future research to focus on the micro-scale aspects,heterogeneous distribution,and long-term stability of GHBS.The discerned patterns and mechanical mechanisms are expected to guide the improvement of predictive model for geo physical-mechanical behavior of GHBS and establish a reference for developing effective strategies for recovery hydrates.