Optimization of in-situ combustion processes: Reduction of CO2 emissions - A preliminary study

Abstract

The in-situ combustion (ISC) process is an enhanced oil recovery (EOR) method that utilizes fuel in place 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, oxygen from the injected air reacts with the oil in place to generate heat, a lighter oil fraction, steam and other reaction products such as CO2. This process drives the upgraded oil towards the production wells, but at the same time produces significant amounts of CO2. In this research project we investigate the potential of a novel hybrid ISC and CO2 recovery and re-injection process, where we attempt to maintain the advantages of the ISC process while at the same time reducing the emissions of CO2. The goal of the study is to test the hypothesis that, as long as the re-injection of produced CO 2 does not extinguish the combustion front, the overall oil recovery should not be greatly diminished. Numerical investigations of a pseudo 2-D model of this hybrid ISC process, using the CMG STARS simulator, show that recycling CO2 back into the reservoir, to replace some of the air typically injected, can be beneficial for reducing the CO2 production but also for increasing the oil production. We observe that the CO2 recycled into the system dissolves readily into the oil phase resulting in lower viscosity oil and in improved production rates. The results of our numerical simulations provide justification for the proposed combined ISC/CO 2-flood process. In this process the ISC provides on site the gas needed for the CO2 flood, and a substantial fraction of the total CO2 produced can be permanently sequestered in the subsurface. Copyright 2009, Society of Petroleum Engineers.