A STEAM CYCLING MODEL FOR GAS PRODUCTION FROM A HYDRATE RESERVOIR

Abstract

A model was developed to compute upper and lower bounds on the expected gas production and the energy efficiency ratio for a single well cyclic steam injection process. This thermal-stimulation model is a time dependent energy balance model with transient heat transfer equations. Wellbore heat losses and heat losses to strata above and below the hydrate zone are considered. The radial advance of the hydrate front is tracked during each cycle to determine gas production, and combustible energy of the produced gas is compared with the energy of the injected steam through the energy efficiency ratio. Production performance was examined for a range of reservoir cases which included variations in reservoir porosity, thickness, and depth. Results indicated that increasing the hydrate-filled porosity or increasing the zone thickness contribute to better gas production and energy efficiency ratios in all cases. Deeper reservoirs appeared to yield more favorable gas production and energy efficiency ratios (in spite of increased wellbore heat losses), a result that is dependent on the natural geothermal gradient. Gas production ranged from the worst estimate of 2.5 MMscf to the best estimate of 110 MMscf in the first year. Corresponding energy efficiency ratios were 4.0 and 9.6, respectively, in spite of steam injection temperatures over 600T.