Simulation of Expanding Solvent - Steam Assisted Gravity Drainage in a Field Case Study of a Bitumen Oil Reservoir

With the increasing demand for energy around the world, more attention is directed to heavy oil and bitumen reservoirs for energy supply. Currently, these high viscosity heavy oil resources are produced primarily by steam. For instance, steam assisted gravity drainage (SAGD) is used widely for the exploitation of bitumen from relatively shallow reservoirs in Alberta, Canada. However, to increase the efficiency of SAGD operations and to improve economics, it has been proposed to add solvent to the injected steam. With solvent injection, there is an increase in the production rate and a reduction in the required injected steam, resulting in a lower steam-bitumen ratio (SBR). Higher concentrations of injected solvent show additional enhancement in oil production rate including some of the solvents. Although simulation results show that the rates of solvent recovery vary depending on the concentration and the nature of solvent used. For optimal results, injection strategy needs to be adjusted depending on the geological conditions, solvent characteristics and reservoir properties. The study presented in paper was motivated by observing promising results of a field test with solvent injection in a SAGD bitumen project. The study began with a compositional thermal simulator to quantify the benefits of solvent addition to the SAGD process (referred to as ES-SAGD) to produce bitumen more efficiently with lower energy requirements. A secondary objective was to determine the optimal and more cost-effective operational protocol for such solvent-steam injection projects. The paper presents (1) the methodology used to model the ES-SAGD enhanced oil recovery process, and (2) reports the field and modeling results of the application of the ES-SAGD process to an oil sand project in Alberta, Canada.