Optimization of in-situ combustion processes: A parameter space study towards reducing the CO2 emissions

Abstract

Enhanced oil recovery (EOR) through in-situ combustion (ISC) is a process that utilizes a fraction of the oil in-place as fuel in order to upgrade and displace the hydrocarbons in heavy oil reservoirs. In ISC processes, air is injected into a heated section of the reservoir. Upon reaching a threshold temperature, the oxygen in the injected air reacts with the oil in-place and generates heat, a lighter oil fraction, as well as steam and other gaseous reaction products, primarily CO2, which help drive the upgraded oil (lighter fraction) towards the production wells. ISC processes can, as a result, be highly efficient but at the same time produce significant amounts of CO2, a potent greenhouse gas. In this paper the emphasis is on developing an ISC process with significantly reduced CO2 emissions. The process involves the capture and re-injection of CO2 into the formation. We find that, in addition to reducing the CO2 emissions, this novel process also shows improved oil recovery rates relative to conventional ISC without CO2 capture and recycle. We observe, for example, increases in the oil recovery of ∼ 33% for a fixed time of operation when comparing the ISC process with CO2 recycle against the conventional ISC process. In addition, at the time when 80% of the total oil in-place has been produced, the CO2 emissions are consistently lowered by 18-22% when CO2 is recycled back into the formation. This study analyzes the characteristics and dynamics of the process and explores the effect of the relevant process parameters. For a wide range of Peclet and Damköhler numbers as well as initial saturations, favorable trends induced by CO2 recycling are observed. © 2011 Elsevier Ltd.