The Impact of Daily and Seasonal Cycles in Solar-Generated Steam On Oil Recovery

Abstract

Abstract Steam-injection projects located in areas with abundant sunshine can exploit solar energy to generate steam, instead of burning gas. Using mirrors, sunlight can be concentrated and used to heat water flowing inside a pipe to steam-temperature at high pressure. This solar-generated steam is only available during the day, causing a day-night cycle in the steam-rate, and is also affected by seasonal variations in solar energy, causing a summer-winter cycle in the steam-rate. Using both analytical modelling and thermal reservoir simulation, we investigate the impact of the daily and seasonal cycles in steam rate on oil recovery. We compare the oil recovery from solar-generated steam and the recovery resulting from a continuous and constant-rate steam-injection, as obtained by burning gas, for instance. Our analytical model for the periodic heating of matrix-blocks in a fractured reservoir shows that for fractured reservoirs with a typical fracture-spacing larger than one metre, the impact of daily cycles in steam-injection can be ignored. Using thermal reservoir simulation, we also compare oil recovery from two representative models of realistic reservoirs: a fractured reservoir (recovery mechanism: thermally-enhanced gas-oil gravity drainage) and a non-fractured reservoir (recovery mechanism: steam-drive), for both steam-injection profiles: constant-rate and cyclic-rate. Our simulations show that the seasonal cycles in the solar-generated steam rate are reflected as seasonal cycles in the oil-rate. The simulation results indicate that for the same cumulative amount of steam injected (during the same time-span), the oil recovery from solar-generated steam-injection and that from constant-rate steam-injection are essentially the same, both for the fractured reservoir and for the non-fractured reservoir. Therefore, from a subsurface oil-recovery point of view, solar-generated steam provides a viable alternative to constant-rate steam-injection.