An Environmentally-Friendly Process for Improved Recovery From Light Oil Reservoirs

Abstract

Abstract The injection of flue gas is a promising cost-effective process for improving recovery from light oil reservoirs. The flue gas could be obtained directly from power plants or other surface sources. It could also be indirectly generated in situ from the spontaneous ignition of oil when air is injected into a high temperature, high pressure (light oil) reservoir. When operating at high pressures commonly found in deep light oil reservoirs, the flue gas may become miscible with the oil, thereby displacing it more efficiently. The efficiency of oil recovery during flue gas injection in light oil reservoirs was studied by flue gas displacements of light oil in a 2.44-m long Berea sandstone core at pressures up to 41.58 MPa and temperature of 116 °C in the laboratory. The laboratory results were history-matched using a compositional simulator. This study attempts to understand and explain the success achieved in field high pressure air injection projects in light oil reservoirs. The high oil recovery obtained from this study suggests that flue gas injection is a promising process for enhanced oil recovery from light oil reservoirs. The results show that the level of oil recovery was accompanied by the level of approach to miscibility between the flue gas and the oil. Both were found to increase with an increase in reservoir pressure, as well as an increase in the carbon dioxide content of the flue gas. When injected from a surface source, the sequestration of the carbon dioxide component of the flue gas (a greenhouse gas) makes the flue gas injection process an environmentally- friendly process. Introduction The solvent extraction and/or miscible-type processes are among the dominant enhanced oil recovery (EOR) methods in Canada(1). These processes include the injection of nitrogen, flue gas, carbon dioxide, hydrocarbon-miscible methods, and solvent extraction of mined, oil-bearing ores(2). They have the potential to add 300 to 400 million cubic metres (~50%) to Canada's remaining recoverable oil reserves(3) and multiples of this to the world's recoverable reserves. Other than compressed air, nitrogen and flue gas are the cheapest gases available(4). The potential for cost-effective oil recovery by flue gas injection from currently producing light oil reservoirs as well as depleted and mature waterflooded reservoirs is most important, especially for reservoirs with little or no water production and those with low porosity and low permeability(5–8) where water injection is not feasible. In recent studies carried out by the authors in a slim-tube apparatus(9–11), flue gas has been found to displace oil by mass transfer of intermediate components of the oil into the injected flue gas, and subsequent condensation of the higher molecular weight intermediates back into the liquid phase from the enriched gas phase through a multi-contact combined vapourizing-condensing gas drive mechanism(12). Although the flue gas may never displace the light oil in a truly miscible fashion because of this mechanism, the oil recovery in such a process is significant enough to make it cost-effective(10).