Field Scale Simulation Study, Investigating the Effect of Geological and Operational Parameters on Solvent Co-Injection Process in Athabasca Bitumen Reservoir

Abstract

Considerable proportions of the hydrocarbon resources in the world are in the shape of heavy oil and bitumen. In an environment of low economic returns for heavy oil operations, Steam Assisted Gravity Drainage (SAGD) process appears very promising from a technical point of view. However, it has two significant deficiencies, namely high energy and water requirements and environmental issues of green house gas (GHG) emissions. Recently, hybrid processes have attracted attentions, since they benefit from advantages of steam and solvents together. The vaporized solvents dissolve into the viscous oil and help the steam to reduce bitumen viscosity dramatically. Moreover, hybrid processes alleviate the high consumption of water and energy while improving the GHG emissions.The goal of this paper is to evaluate and compare the efficiency of SAGD and solvent co-injection (SCI) using experimental PVT properties of the Athabasca bitumen and a thermal numerical reservoir simulator. Steam trap control was applied in this study to hamper the steam production. Sensitivity analysis was performed to find out the effects of various geological parameters such as reservoir thickness, horizontal and vertical permeability, horizontal and vertical shale barriers and reservoir pressure, as well as operational parameters like injector location, solvent diffusivity, different solvent types and different concentrations of injected solvent. Three different crude oils from Cold Lake, Athabasca and Lloydminster reservoirs were selected to investigate the effect of viscosity.Results divulged great recovery of bitumen and reasonable amount of steam-oil ratio (SOR) for both processes. Applying solvent co-injection with steam reduced the amount of steam required and consequently decreased SOR, while higher recovery factors (R.F.) were obtained. Butane, pentane, hexane, heptane and dodecane were tested solvents in this study. Among them, hexane was used to investigate the effect of solvent concentration. Using higher concentration of injected solvent resulted in higher R.F. and lower SOR, however, economy of the process regarding the use of highly valuable solvents should also be considered.Higher vertical, horizontal permeability and reservoir pressure had positive effect on oil production. In addition, thicker reservoir showed better and more economical results in terms of oil production and SOR.Presence of shale barrier has a negative effect on oil production. This negative effect is more pronounced in case of horizontal than vertical shale layers. Applying solvent diffusivity coefficients revealed that very fine grid system in three directions is needed to evaluate the effect of diffusion precisely.