Production Strategy of Oceanic Gas Hydrate Reservoirs using Various Well Configurations

Hydrates are ice-like crystalline structures in which gas molecules are trapped under low temperature and high-pressure conditions. Methane hydrate reservoirs are found in arctic region, where temperature is low, and in oceanic sediments, where pressure is high. Recent production test in Nankai trough shows the production potential from oceanic sediments using depressurization. In this work, we investigate the effect of initial pressure, temperature, saturation, and well configurations on the production potential of oceanic gas hydrate reservoirs. We use an in-house multi-phase, multi-component, thermal, three-dimensional, finite volume reservoir simulator to study Class-2 hydrates. Three components (water, methane, and hydrate) and four phases (gas, aqueous-phase, hydrate and ice) are considered in the simulator. Energy and mass balance equations are solved in space and time domain. The aquifer layer below the hydrate-bearing zone can be confined or unconfined. We consider different configuration of horizontal wells, vertical wells and combinations of the horizontal and vertical wells to investigate the production potential of the reservoirs. Horizontal wells are found to be more effective for gas production than vertical wells in gas hydrate reservoirs. Gas production by depressurization is ineffective in unconfined hydrate reservoirs even with horizontal wells. Warm water injection is necessary for gas production from unconfined hydrate reservoirs. If the horizontal wells are located in the hydrate-bearing zone, the low permeability of the near well zone leads to negligible gas production in the initial periods.