Non-Isothermal, Multi-phase, Multi-component Flows through Deformable Methane Hydrate Reservoirs

TL;DR

This paper develops a comprehensive hydro-geomechanical model for methane hydrate reservoirs, integrating kinetic hydrate phase change, non-isothermal multi-phase flow, and soil deformation to better understand subsurface hydrate dynamics.

Contribution

It introduces a novel decoupling strategy and numerical scheme for modeling complex hydrate reservoir processes, emphasizing the coupling of kinetics, flow, and geomechanics.

Findings

Hydrate dissociation significantly affects pore pressure and soil stability.

Coupling hydrate phase change with poroelasticity is crucial for accurate simulations.

Numerical examples demonstrate the model's ability to simulate hydrate melting and ground subsidence.

Abstract

We present a hydro-geomechanical model for subsurface methane hydrate systems. Our model considers kinetic hydrate phase change and non-isothermal, multi-phase, multi-component flow in elastically deforming soils. The model accounts for the effects of hydrate phase change and pore pressure changes on the mechanical properties of the soil, and also for the effect of soil deformation on the fluid-solid interaction properties relevant to reaction and transport processes (e.g., permeability, capillary pressure, reaction surface area). We discuss a 'cause-effect' based decoupling strategy for the model and present our numerical discretization and solution scheme. We then identify the important model components and couplings which are most vital for a hydro-geomechanical hydrate simulator, namely, 1) dissociation kinetics, 2) hydrate phase change coupled with non-isothermal two phase two component flow, 3) two phase flow coupled with linear elasticity (poroelasticity coupling), and finally 4) hydrate phase change coupled with poroelasticity (kinetics-poroelasticity coupling) and present numerical examples where, for each example, one of the aforementioned model components/couplings is isolated. A special emphasis is laid on the kinetics-poroelasticity coupling. We also present a more complex 3D example based on a subsurface hydrate reservoir which is destabilized through depressurization using a low pressure gas well. In this example, we simulate the melting of hydrate, methane gas generation, and the resulting ground subsidence and stress build-up in the vicinity of the well.