Optimization of Steam and Solvent Injection as an Improved Oil Recovery Method for Heavy Oil Reservoirs

Currently a resource more and more used by the petroleum industry to increase the efficiency of steam flood mechanism is the addition of solvents. The process can be understood as a combination of a thermal method (steam injection) with a miscible method (solvent injection), promoting, thus, reduction of oil viscosity and interfacial tensions between injected fluid and oil. Solvents are hydrocarbons well known for reducing these tensions and facilitating the production of heavy oil. The use of solvent alone tends to be limited because of its high cost. When co-injected with steam, the vaporized solvent condenses in the cooler regions of the reservoir and mixes with the oil, creating a zone of low viscosity between steam and heavy oil. Mobility of the displaced fluid is then improved, resulting in an increase of oil recovery. To better understand this improved oil recovery method, a numerical study of the process was done contemplating the effects of some operational parameters (distance between wells, steam injection rate, solvent type and injected solvent volume) on cumulative oil production and oil rates. A semi synthetic model was used. Some reservoir data were obtained similar to those found in Brazilian Potiguar Basin and others ones were obtained from literature. Simulations were performed in STARS (CMG, 2007.11). It was found that injected solvent volumes increased oil recovery and oil rates. Further, the majority of the injected solvent was produced and can be recycled. High initial productions achieved by models that use solvent have normally a significant impact on the operation economics, because earlier productions suggest that fluids injection (steam and solvent) can be interrupted earlier. On environmental point of view, it would have a reduction of energy and water consumptions for steam generation, having diminished Green House Gases (GHG) emissions. Also it is important to emphasize that the high oil rates presented by these models can generate an earlier financial return, and this would be decisive for the economic viability of the project.