Strategizing well locations in unconfined, heterogeneous hydrate reservoirs for maximizing gas production

Natural gas hydrates are a potential alternative to conventional energy due to their high energy density and low carbon with wide distribution across the globe. Producing methane from the gas hydrate reservoirs is technically challenging as they are present in complex geological environments which are highly heterogeneous. In this work, using numerical reservoir simulations of gas production from oceanic gas-hydrate reservoirs underlain with an aquifer we show that warm-water injection is necessary when the water layer below the hydrates is unconfined. Our simulations reveal that the aquifer characterization is essential to design the gas production strategy and estimating the gas recovery. We demonstrate that for a gas-hydrate reservoir attached to a moderately unconfined aquifer, warm-water injection in the hydrate-zone leads to more recovery. If the hydrate-zone is layered then the gas recovery improves by injecting the water into a more porous layer. However, for highly unconfined reservoirs water should be injected near the aquifer for efficient recovery of gas. Our findings will help in developing gas production plans from the hydrate reservoirs around the world.