Multi-Phase Coupled THMC Modeling of Gas Extraction from Hydrate Reservoirs

Abstract

The unconventional source of energy such as the methane gas hydrate sediments are typically found in substantial quantities in permafrost regions and in deep-sea continental shelves. Extracting gas from these hydrate sediments might result in problems associated with seafloor subsidence, well-bore collapse, and submarine landslides. During gas extraction, there are various physical processes that are commonly observed such as thermal changes, dissociation of hydrates, the flow of fluids, and the deformation of the geomaterial. Thus, to understand all these processes, an appropriate multi-physics numerical model needs to be developed which can quantify the gas production due to the dissociation of hydrates coupled with solid deformation. Further, in order to take into account the effect of hydrate saturation on mechanical strength and stiffness, an advanced elastic-plastic constitutive (HISS-MH) model for gas hydrate sediments was used. In this study, a thermo-hydro-mechanical-chemical model was developed using the finite volume method (for mass balance and energy equations) and the finite element method (for geomechanics equations). After the numerical implementation and validation, the effect of various well-bore positions along the reservoir's depth on the settlement and cumulative gas production was investigated. A well-bore at the top, middle, and bottom of the reservoir are the three distinct scenarios that are independently examined. The bottom well-bore has the lowest overall settlement, while the middle well-bore has the highest after one year of gas production. A well-bore in the middle of the reservoir is preferable due to its greater overall gas production and least differential settlement.