Warm Water Flooding of Unconfined Gas Hydrate Reservoirs

Abstract

Large quantities of natural gas hydrates are present in shallow marine sediments as well as in arctic regions. This research is aimed at assessing production of natural gas from unconfined marine hydrate deposits. A multiphase, multicomponent, thermal, 3D simulator is used to simulate production of hydrates in the equilibrium mode. Three components (hydrate, methane, and water) and four phases (hydrate, gas, aqueous-phase, and ice) are considered in the simulator. Depressurization and warm water flooding of unconfined, horizontal and dipping reservoirs have been simulated. Production of methane from gas hydrate reservoirs depends on reservoir confinement, injection temperature, injection pressure, and production pressure. For unconfined horizontal reservoirs, depressurization is ineffective; thermal stimulation is necessary for gas production. Even warm water (temperature ≈ 30 °C) injection improves the gas production from hydrate reservoirs. Lower vertical permeability helps the gas production by heating a larger area of the reservoir for hydrate dissociation. As the well spacing decreases, the gas production rate increases. Depressurization alone is effective in dipping unconfined reservoirs, but much slower than warm water injection. As the injection point of the warm water moves down the reservoir, the start of the high gas recovery phase gets delayed, but the time for completion of gas recovery becomes shorter.