Experimental and Theoretical Investigation on Decomposition of Hydrate-bearing Layer by Full Implicit Simulator of Hydrate

Abstract

The gas-liquid production behaviors of hydrate-bearing layers involve the coupling of thermal-hydraulic-chemical (THC) multi-physical fields. The behaviors of methane hydrate dissociation in porous sands by pure depressurization and thermal-assisted depressurization methods via a single vertical well are investigated in a cuboid high-pressure reactor (CPR). Numerical models are developed to quantify the physical and chemical processes of fluid flow in porous media. The simulation results suggest that key indicators, including the gas and water production profiles, the spatial distributions of pressure, temperature, and phase saturations, and component mass, all agree well with the experimental data. It also clarifies the evolution of the dissociation front of methane hydrate in porous sands under the synergy effect of depressurization and electrical heating, and visualizes the complex hydrate dissociation mechanisms that are technically difficult to be measured in the experiment. In the earlier (0-160 min in Reference Case) and later (160-280 min) stages of hydrate dissociation, the kinetics and heat transfer are the dominant factors, respectively. The key finding is that the laboratory trials of pressure-induced and thermal-assisted methane hydrate reactions can be reproduced faithfully by numerical models with a group of unaltered parameters. By minimizing the deviations between numerical simulations and experimental data (less than 10 %), this study gives some deep insight into the determination of key parameters in the coupled THC system affecting hydrate dissociation, including the thermal conductivity of quartz sands ${\lambda }_s$ = 2.4 W/m/K, the absolute permeability $k_0$ = 21.1 D, and the adjustment factor $F_A$ = 0.03 in the kinetic model of methane hydrate dissociation. It is noteworthy that the mathematical models and the above parameters apply to both of the two simulated cases of methane hydrate dissociation under depressurization and thermal stimulation.