Research on hydrate-bearing reservoir deformation and wellbore wall stability during natural gas hydrate exploitation

Abstract

Marine natural gas hydrate currently attracts increasing research attention as a potential resource of alternative clean energy. However, exploitation disturbance threatens the stability of the wellbore wall as the physical parameters and mechanical properties of hydrate-bearing reservoirs change due to hydrate decomposition, which causes the futility of conventional analysis. This study determines the influence of production disturbance on wellbore wall stability by solving the fluid–solid coupling model during the hydrate decomposition based on a self-developed solver. Through this model, the conditions of depressurized hydrate production are simulated to obtain the horizontal deformation and settlement laws of hydrate-bearing reservoirs and overburden layers. These deformations and settlements cause uneven horizontal in-situ stress on hydrate-bearing reservoirs, which will cause wellbore wall instability during hydrate production. Results show that the middle of the hydrate-bearing reservoir is the best depressurization position for production. In addition, production time, production pressure, and reservoir permeability are the key factors that affect the hydrate decomposition and cause inhomogeneous in-situ stress. The borehole wall first destabilizes at the minimum effective horizontal stress direction. Results can provide a reference for the safe and efficient exploitation of marine NGH.