Semianalytical Modeling of Steam/Solvent Gravity Drainage of Heavy Oil and Bitumen: Unsteady-State Model With Curved Interface

Summary Coinjection of solvent with steam in steam-assisted gravity drainage (SAGD) has shown promising results for enhancing oil rates as well as reducing energy and water consumption. Modeling and optimizing hybrid-steam/solvent-recovery processes by use of commercial numerical simulators can be very time-consuming. Semianalytical mathematical models may be used to estimate production rates and thermal efficiency in much less time. In this study, an unsteady-state semianalytical model was developed to predict the oil-flow rate in the steam/solvent-assisted-recovery process. The model assumes a curved interface with transient temperature and solvent distribution in the mobile zone. It also accounts for transverse dispersion and concentration-dependent molecular diffusion for solvent distribution. The oil-flow rate and interface profile are predicted at each time in an iterative fashion. The model is validated against the CMG-STARS thermal simulator as well as experimental results for hexane-aided SAGD physical-model tests. The semianalytical model was able to predict oil-production rates by use of different solvents coinjected with steam, in agreement with reported experimental data. The proposed model accounts for the complex interaction of heat and solvent solubility and diffusion as they affect mobilization and production of viscous oil. This model may be used to estimate the optimal operation parameters for the process over a range of different reservoir qualities and pressures, in a very time-efficient manner. The final outcome may lead to an efficient design of a steam/solvent-recovery process that uses less water and reduces the amount of energy and gas emissions per barrel of oil produced.