Life Cycle Assessment of Improved Oil Recovery While Helping to Achieve Net Zero Emissions from Shale Reservoirs

Abstract

Summary Shale reservoirs will help to meet oil demand that is forecasted to continue increasing for several years. Oil recovery from shales is low and has been reported to range between 5% and 10%. The objective of this paper is to show how oil recovery from shale can be improved while simultaneously reducing CO2 emissions, thus contributing to the goal of a net-zero future. The proposed methodology shows how oil recovery from shales can be increased while simultaneously storing CO2 in undepleted (as opposed to depleted) shale oil reservoirs and consequently contributing to a future with net-zero emissions. The methodology is developed with the use of reservoir simulation and is achieved by performing the following procedure: (1) Start huff ’n’ puff CO2 injection 2 or 3 years after the well goes on oil production so the shale reservoir is essentially undepleted, and (2) store CO2 gradually in the shale reservoir during the huff periods, and continuously once the huff ’n’ puff project is finalized. The simulation model includes a history match period with actual production data from a pilot horizontal well and a forecast period with huff ’n’ puff CO2 injection. Two cases, one with diffusion and one without diffusion, are conducted for evaluating the molecular diffusion effect. The initial reservoir pressure is never exceeded during the life cycle of the project as a safeguard against the possible creation of new fractures or reactivation of faults. Life cycle assessment (LCA) indicates that the ratio of cumulative stored CO2 to cumulative equivalent CO2 emissions during the project is approximately 31.3%, helping us consequently in the goal to eventually achieve a future with net-zero emissions. A careful literature survey indicates that the methodology proposed in this paper that includes enhanced oil recovery (EOR) by huff ’n’ puff CO2 injection and the simultaneous storage of CO2 in the shale reservoir is novel and has not been considered previously in geoscience or petroleum engineering literature.