Effects of net-zero produced water strategy on gas production and sediment deformation in marine gas hydrate reservoirs

Gas hydrates, commonly found in deep marine sediments, have been considered a potential long-term energy source. Recent field trials demonstrated that well depressurisation, converting solid gas hydrates into fluid in-situ, is the most efficient method for gas production. However, this process involves continuously pumping a large volume of water from the ocean that cannot be simply disposed of due to environmental concerns. The produced water, with different temperature, salinity, and residues from shallower seawater, could impact marine species, habitats, and ecosystems if directly discharged into the sea. Storing or transporting this water for treatment is economically impractical. Furthermore, as hydrate dissociation increases sediment permeability, water production rates rise over time. Therefore, reinjecting produced water into gas hydrate reservoirs emerges as a promising net-zero produced water strategy. This study investigates the effects of produced water re-injection on gas productivity and sediment deformation through coupled thermo-hydro-chemo-mechanical numerical analysis. The results indicate that re-injecting the water could improve gas productivity but may cause heave and differential displacement near the injection well. This highlights the importance of considering thermo-hydro-chemo-mechanical processes in comprehensively evaluating energy production strategies and suggests that further studies are necessary for future commercial gas production from gas hydrate reservoirs.