Gas Production Optimization from 3D Hydrate Dissociation via Depressurization in Multiply Fractured Reservoirs

Natural gas hydrate (NGH), a clean energy resource with vast reserves and high energy density, holds significant potential to address global energy demands. However, its commercial exploitation remains challenging due to low dissociation efficiency under conventional extraction methods. To address this limitation, this study investigates the synergistic effects of hydraulic fracturing and depressurization on enhancing NGH mining. A three-dimensional model is developed using the commercial package, TOUGH + HYDRATE, to study the NGH dissociation by depressurization from a single horizontal well intercepted by multiple hydraulic fractures. After a sensitivity analysis is carried out, a quantitative relationship between the fracture density (N_d), depressurization amplitude (P_w) and the gas production performance is established. The results reveal that the dissociation rate in the case with fractures is several orders of magnitude higher than that in the case without fractures. Notably, the impact of N_d on production diminishes at higher N_d values. Increasing N_d from 1 to 3 enhances cumulative gas release by over 30%, whereas further increases to N_d = 4 and 5 yield only about 18% incremental gains. Additionally, at small depressurization amplitudes (P_w = 0.8P₀–0.9P₀), fracture density exerts minimal influence on dissociation efficiency due to insufficient driving forces. Spatial analysis shows that dissociation fronts initially form and propagate near the wellbore, but later exhibit near the upper and lower boundaries of the NGH layer. The gas distribution gradually increases during the initial year, but subsequently concentrates only near advancing fronts, driven by fluid influx from adjacent strata and the presence of high-permeability flow channels. These findings demonstrate that optimizing fracture density and depressurization amplitude is critical for balancing extraction efficiency, providing actionable insights for designing field-scale NGH production strategies.