Efficient oil displacement near the chamber edge in ES-SAGD

Steam-assisted gravity drainage (SAGD) is the most widely used method for in-situ bitumen recovery. Expanding-solvent-SAGD (ES-SAGD) has been proposed as an alternative to SAGD to improve its efficiency. In ES-SAGD, steam is coinjected with a small amount of solvent. Detailed oil recovery mechanisms near the chamber edge are little known due to the complex interaction of fluid and energy flow, and phase behavior. Prior research on ES-SAGD explains that coinjected solvent can further decrease oil viscosity near the chamber edge by dilution, in conjunction with heat. In this paper, we conduct a detailed investigation on oil displacement mechanisms and the placement of solvent near the chamber edge using fine-scale reservoir simulation. The importance of properly considering both phase behavior and flow to design ES-SAGD is demonstrated. Results show that ES-SAGD can achieve a higher displacement efficiency than SAGD. Oil production rate in ES-SAGD can be two times higher than that in SAGD. As a result, the ultimate oil recovery of ES-SAGD is enhanced by almost 20%, compared to SAGD in this research. The oil saturation reduction results from condensed solvent bank and phase transition near the chamber edge. The condensed solvent bank lowers the oil-component concentrations there. The diluted oil with solvent is then redistributed in the gaseous and oleic phases in the presence of the water phase on the phase transition at the chamber edge. The resulting amount of the oleic phase can be significantly small, yielding lowered oil saturations in the ES-SAGD chamber. (C) 2014 Elsevier B.V. All rights reserved.