Mass and heat transfer in developing fracture-filling gas hydrate using a fractured horizontal well

Natural fractures are widely distributed in hydrate reservoirs, resulting in a fracture-filling type of gas hydrate. However, the complexity of fracture networks, including both hydraulic and natural fractures, complicates the evaluations of gas well productivity. This study investigates the heat and mass transfer dynamics in fracture-filling gas hydrate reservoirs developed using a multi-stage fractured horizontal well. A coupled thermal-hydraulic-mechanical model was developed based on the embedded discrete fracture method, and the model was validated against a commercial numerical simulator, demonstrating high accuracy in predicting gas–water production rates and reservoir pressure, temperature, and hydrate saturation field evolution. The simulation results revealed significant insights into gas and water production rates, flux distributions, and field map distributions. Furthermore, we analyzed the impact of various hydraulic fracture parameters, including fracture numbers, angles, lengths, and morphologies. The simulation results show that fractured wells perform better than non-fractured wells, and the initial daily gas production of a multi-stage fractured horizontal well is 4.05 times that of a fractured vertical well. Besides, fracture geometry critically influences the productivity of the multi-stage fractured horizontal well. The greater the number of hydraulic fractures and the longer the fracture length, the higher the daily and cumulative gas production of the gas well due to higher drainage areas. The cumulative gas production is increased by 131.98% as the number of hydraulic fractures is increased from 3 to 9, whereas the increase is 91.66% as the fracture length is increased from 50 to 200 m. A narrower intersection angle between hydraulic fractures and the wellbore corresponds to a diminished drainage area, thereby exacerbating fracture-driven interference effects and accelerating production decline rates. The intersection density between hydraulic fractures and natural fracture systems serves as the primary determinant of drainage efficiency in fracture-filling gas hydrate reservoirs. The findings have important implications for improving gas well productivity and enhancing the efficient exploitation of fracture-filling gas hydrates.