Coupling Model of Submarine Deformation Response Prediction during Methane Hydrate Exploitation

Abstract

Methane hydrate (MH) dissociation will decrease the strength of methane hydrate-bearing sediments (MHBSs) and induce the deformation of the submarine sediment. Considering that such deformation could trigger the submarine landslide during the gas production, it is essential to understand it correctly. However, few studies have investigated a MH exploitation of what scale could affect the submarine slope stability and sand production near the wellbore. The present study adopted the numerical simulation approach where a thermal-fluid-mechanical coupled model was established. Then, the deformation response of a marine slope was analyzed considering the influence of the slope angle, the cyclic loading condition, and the decompression amplitude condition, during MH exploitation. Depressurization in a vertical well was used as the exploitation technique. According to the obtained results, when the slope angle is horizontal, the MHBS layer and the upper sediment layer deform around the wellbore symmetrically; the deformation degree increases and deformation distribution expands with the increase in loading amplitude and decompression amplitude. The exceeding pore water pressure in the upper sediment layer increases more significantly with the increase in loading amplitude. The MH regeneration area will be formed more efficiently with the increase in loading amplitude. The higher the decompression amplitude is, the wider the MH dissociation area will be. It was also found that sand production always starts on the upper and the bottom sections of the MHBS layer around the wellbore, and the predicted distance of sand production increases with the increase in mining time. The research results lay the theoretical foundation for the accurate understanding of the MHBS layer as well as the marine sediments’ stability and sand production during natural gas production from MH reservoirs.