A 3D modeling study of effects of heterogeneity on system responses in methane hydrate reservoirs with horizontal well depressurization

Production tests in marine methane-bearing sediments have been carried out worldwide. Pilot horizontal well tests have exhibited the potential of using horizontal well depressurization for methane hydrate production. Many studies have focused on the 2D thermal-hydraulic-mechanical-chemical (THMC) responses induced by horizontal wells, which targeted certain vertical planes penetrating the well, while 3D numerical modeling of the associated heat and mass transfer behaviors and induced geomechanical responses can provide behaviors not captured by 2D modeling. Additionally, it can give elaborated results in heterogeneous cases. This study investigates the effects of heterogeneity caused by interlayers on the coupled THMC behaviors in a 3D domain depressurized by a horizontal wellbore. Full geomechanics is considered in the model. The model is verified against a widely used benchmark problem. Numerical results show that, due to the nature of 3D fluid flow induced by depressurization, flow patterns in vertical and horizontal directions are different, which leads to the phenomenon that the system response patterns captured by 3D THMC modeling are different from those in 2D THMC modeling. 2D THMC modeling may simplify the coupled THMC system response with the presence of horizontal wells. Also, the system response is mainly governed by the thickness of hydrate-free interlayers in heterogeneous cases. The effect of heterogeneity on pressure is observed in all investigated locations while its effect on temperature and displacement is only observed in planes penetrating the wellbore. The negative impact of heterogeneity on methane production is magnified by thicker hydrate-free interlayers.