Application of Solvent Alternating SAGD Process to Improve SAGD Performance in Athabasca Bitumen Reservoir

Abstract

Abstract Canada, Venezuela and United States contain the largest portions of heavy oil and bitumen resources throughout the world. The problem associated with this type of resource is very viscous fluid flow. The EOR methods applied to heavy oil reservoirs are mainly based on viscosity reduction processes such as heating the reservoir and solvent injection. Heating, in the form of hot water flooding, steam injection and in-situ combustion dramatically reduces the viscosity of heavy oil and bitumen, but it has green house gas (GHG) emission problems. Diffusion of solvents in heavy oil makes it lighter and therefore mobile and producible via production well. Diffusion of solvent is a very tardy process while time is very important in oil industry and any delay results in extra costs. Recently, hybrid methods like solvent and steam co-injection, steam alternating solvent injection (SAS) have been introduced to solve the mentioned problems, while benefiting from the advantages of heat and solvent. Several simulation studies were performed to evaluate and compare the performance of steam assisted gravity drainage (SAGD) and steam alternating solvent (SAS) processes. Athabasca bitumen reservoir properties were used. Effects of some reservoir and fluid parameters such as thickness, porosity, vertical to horizontal permeability ratio and viscosity were assessed and compared for both processes. Experimental viscosity data of Athabasca and Cold lake bitumen were applied to evaluate the viscosity effect. In addition, sensitivity analysis was carried out on injection time intervals of solvent, solvent type and concentration. Results revealed high recovery of bitumen and appropriate steam-oil ratio (SOR) for both processes. However, SAS showed better performance using hexane as a solvent. Lower porosity, vertical to horizontal permeability ratio and thickness resulted in higher SOR for SAGD process while they had no major effect on SAS. Higher concentration of injected solvent resulted in faster recovery performance and lower SOR. Pentane and heptane were used as alternatives for hexane to investigate the impact of the selected solvent. They divulged almost the same results as hexane. Different injection intervals of 3, 6, 9 months and a year were also studied and the analogous results were obtained.