SPE 153806 Solar-Generated Steam for Oil Recovery: Reservoir Simulation, Economic Analysis, and Life Cycle Assessment

Integrated solar thermal steam generation and heavy-oil recovery projects have garnered interest because of their ability to decrease the variability of steam generation costs arising from fluctuations in natural gas prices as well as life-cycle carbon dioxide emissions. The viability of a solar thermal steam generation system (with and without natural gas back-up) for thermal enhanced oil recovery (TEOR) in heavy-oil sands was evaluated in this study. Using the San Joaquin Valley as a case study, the effectiveness of solar TEOR was quantified through reservoir simulation, economic analysis, and life-cycle assessment of oil-recovery operations. Reservoir simulation runs with continuous but variable rate steam injection were compared with a base-case Tulare Sand steamflood project. Reservoir properties and well geometries were drawn from the literature. For equivalent average injection rates, comparable breakthrough times and recovery factors of 65% of the original oil in place were predicted, in agreement with simulations in the literature. Daily cyclic fluctuations in steam injection rate do not greatly impact recovery for this reservoir setting. Oil production rates for a system without natural gas back-up to moderate injection rates do, however, show seasonal variation. Economic viability was established using a discounted cash flow model incorporating historical prices and injection/production volumes from the Kern River oil field. This model assumes that present day steam generation technologies could be implemented fully at TEOR startup for Kern River in 1980, for the sake of comparison against conventional steam generators and cogenerators. All natural gas cogeneration and 100% solar fraction scenarios had the largest and nearly equal net present values (NPV) of $12.54 B and $12.55 B, respectively, with production data from 1984 to 2011. Solar fraction refers to the steam provided by solar steam generation. Given its large capital cost, the 100% solar case shows the greatest sensitivity to discount rate and no sensitivity to natural gas price because it is independent of natural gas. Because there are very little emissions associated with day-to-day operations from the solar thermal system, life-cycle emissions for the solar thermal system are significantly lower than conventional systems even when the embodied energy of the structure is considered. Here, we estimate that less than 1 g of CO2/MJ of refined gasoline results from the TEOR stage of production if solar energy provides all steam. By this assessment, solar thermal based or supplemented steam generation systems for TEOR appear to be a preferred alternative, or supplement, to fully conventional systems using natural gas (or higher carbon content fuels), especially in areas with large solar insolation. Introduction The objective of this paper is to investigate the impacts of using solar energy rather than natural gas to generate steam for Thermal Enhanced Oil Recovery (TEOR). Multiple metrcs are used to evaluate solar TEOR: reservoir performance, economics, and environmental impact. Unlike previous studies (van Heel et al., 2010) this paper considers feasibility more broadly than at the reservoir level and roots this discussion on actual projects in the San Joaquin Valley (USA) rather than an idealized, analytical model. From a reservoir engineering perspective, the major challenge in implementing a solar thermal based system is to determine the interplay of oil production and the daily cycles in heat production caused by the rising and setting of the sun as well as the yearly cycle caused by the changing of the seasons. From an economics standpoint, it is important to show that a solar TEOR project has profits at least equal if not in excess of conventional systems, such as natural gas cogeneration, by which most steam is generated for TEOR (Molchanov, 2011). And lastly, from an environmental perspective, it is important that sources of “green” energy provide actual benefits in their life-cycle impacts (relative to conventional sources), whether from an energy or emissions perspective. By benchmarking the performance of current solar thermal technologies against conventional fossil fuel systems in this way, we hope to highlight the strengths and weaknesses