Modeling Fracturing Propagation in Hydrate Bearing Sediments Using Phase Field Method

Abstract

Fracture development in natural gas hydrate reservoirs plays a critical role in enhancing permeability for gas production while potentially triggering geomechanical hazards due to hydrate dissociation. This study presents a fully coupled thermo-hydro-mechanical-chemical phase-field model to simulate fracture propagation in hydrate-bearing sediments. The model integrates thermal effects, two-phase flow, hydrate phase change and poroelastic deformation. Fracture evolution is governed by a diffusion-type phase-field variable, driven by maximum positive stored energy considering the strain energy, pore pressure and water/gas saturation, with its growth modulated by hydrate saturation and fracture energy release rate function. Fracture-induced alterations in permeability, porosity, and Biot's coefficient; along with hydrate dissciation-induced variation in bulk modulus, permeability, and heat/mass source, are systematically incorporated to account for coupled multiphysics processes. The model is numerically implemented within a finite element framework using a fully coupled direct solver with damped Newton-Raphson scheme to efficiently solve the strongly nonlinear coupled multiphysics problem. Model validation is encompasses three benchmarks: 1) comparison with analytical Sneddon's fracture displacement solution, 2) Numerical benchmarking against unsaturated fracture flow simulations, and 3) Experimental calibration using hydrate sediment breakdown pressure data. These validations confirm the model capability, and suitability in capturing THM-coupled responses and its applicability to hydrate fracturing scenarios. An application simulating hot water injection into hydrate-bearing sediments further illustrates the model’s ability to capture fracture evolution and reservoir response. This work provides a robust framework for simulating fracturing in NGH systems, with implications for optimizing production strategies and assessing geotechnical risk in future comercial hydrate exploitation.

Keywords: Natural gas hydrate, Hydraulic fracturing, Fracture propagation, Phase-field method, THMC coupling, Unsaturated porous media