Thermo-hydro-mechanical effects of hydraulic fracturing on depressurization-induced gas production from natural gas hydrate reservoirs: a numerical study

Abstract

A MATLAB-based thermo-hydro-mechanical (THM) simulator incorporating the Snow equivalent-permeability tensor was developed for hydraulic-fracturing-assisted depressurization of natural gas hydrate reservoirs in a two-dimensional axisymmetric domain. Validation against Shenhu field-production data, TOUGH+Hydrate benchmarks, and laboratory datasets yielded R² values of 0.941–0.992 for the evaluated responses. Hydraulic fractures provide high-conductivity pathways that markedly extend pressure depletion, while endothermic dissociation causes pronounced local cooling (maximum 11.4 K adjacent to fracture surfaces), inducing secondary hydrate formation within approximately 22 m of the fractures and reducing cumulative gas production by about 11% over 200 d. Modeled effective stresses exceed 14 MPa along 50–60 m of the fracture planes, and stress-dependent aperture closure and compaction-induced permeability deterioration are captured through coupled porosity–permeability feedback. Under the baseline slope conditions, pore-pressure depletion and cementation loss reduce the calculated submarine-slope factor of safety from 1.55 to 0.99 within one year (− 36%), with predicted seafloor subsidence of 0.36–0.72 m. Sensitivity analysis identifies fracture aperture as the dominant geometric parameter (a sixfold increase raises the modeled peak rate by 122%) and indicates a preliminary favorable range of nf = 3–4 and lf = 9–12 m, with the aperture near the upper bound of the tested range.