A novel model of reaction specific surface area via depressurization and thermal stimulation integrating hydrate pore morphology evolution in porous media

Abstract

Reaction specific surface area (RSSA) of hydrate is essentially important for hydrate kinetic dissociation and gas production from hydrate-bearing sediment. Models of RSSA available in literatures neglecting hydrate pore morphology evolution and methods induced hydrate dissociation could not capture the characteristic of RSSA evolution accurately. In this study, a novel model using logistic function to link microscale hydrate pore morphology evolution with macroscale RSSA variations was proposed, and verified by different published laboratory data and compared with other models. The introduced critical hydrate saturation and transitional intensity of hydrate pore morphology were optimized by genetic algorithm. Results indicated that the critical hydrate saturation and transitional intensity of hydrate pore morphology dominated the characteristics of RSSA evolution. The RSSA evolution was orderly divided into four stages named ‘high Sh pore wall coating dominated’, ‘high Sh pore filling dominated’, ‘low Sh pore filling dominated’ and ‘low Sh pore filling only’ in both method of hydrate dissociation by depressurization and thermal stimulation. In addition, the RSSA for depressurization was lower than that of thermal stimulation at the same hydrate saturation due to annulus hydrate by thermal stimulation. Grain size and arrangement factor significantly influenced RSSA, which showed a negative correlation. The proposed model brings reliable predictions and mechanistic understandings of the RSSA evolution in hydrate-bearing sediment, and builds fundamental theory for development of natural gas hydrate in safety and efficiency.