Numerical analysis of sand production during natural gas extraction from unconsolidated hydrate-bearing sediments

Abstract

Sand production, which poses a great challenge for sustainable methane gas production, is commonly encountered during natural gas extraction from unconsolidated hydrate-bearing sediments. However, studies on the subject are still limited. This paper provides a numerical model, coupled with thermo-hydro-mechanical (THM) processes, which is capable to characterize the process of sand production in gas hydrate-bearing sediments. The numerical simulator is developed by introducing the newly developed particle migration module into the existing framework of the THM coupled simulator HydrateBiot. The dynamic of sand production was investigated numerically, and the influence of various parameters on sand, gas and water production was studied. The simulation results show that particle detachment and migration mainly occurs in the vicinity of wellbore, while lowering the depressurization rate can mitigate sand production to some extent without significantly inhibiting the gas production. The using of the sand control device can effectively inhibit sand production, but its blockage will cause a significant drop in gas productivity. Sensitivity analyses of the critical fluidization velocity and solid-liquid velocity show that the increase of solid particle concentration will significantly affect the fluidity of water, thus affecting the depressurization process and gas productivity. It is also found that the massive particle detachment and migration may cause the appearance of clogging area in the vicinity of the wellbore and severely restrict the sustainable gas production. The numerical model and analysis presented here could provide useful insight into sand detachment, migration and production processes induced by methane gas production using depressurization method in the hydrate-bearing marine sediments.