Abstract
In the mathematical treatment and numerical simulation of hybrid recovery processes, specifically SAGD (Steam-Assisted Gravity Drainage) with solvents, instantaneous phase equilibrium is assumed. Previous studies by the authors, and others, show that this is not the case. Experimental work and the lack of success in the field corroborate this view. In the present work, a non-equilibrium model is developed involving the solution of mass and heat transfer equations. The state of equilibrium is based on diffusion and dispersion at the pore scale.
First, a new model is developed for oil mobilization by solvent and heat based on diffusion and dispersion mechanisms for different solvents. The concentration distribution is used to calculate the partition coefficients in a gridblock based on temperature, pressure, composition, and apparent time. The latter is different from simulation time and is an indicator of gridblock interaction with the solvent. By defining new parameters viz. apparent time, a gridblock has a memory of how long it was in contact with the solvent.
The analytical model developed in the first phase of this work confirmed the need for a non-equilibrium model for reservoir simulation. The non-equilibrium partition coefficient developed for vapor solvents of methane, propane, and butane using compressible assumption for the vapor phase. The oil production appears to improve using a solvent if instantaneous equilibrium is assumed. In this study, the nonequilibrium approach developed for heated solvent showed the cumulative oil production decreased as a result of the inability of the solvent to reduce viscosity.
The present study is the first of its type in the development of a non-equilibrium pore-scale simulator. The outcome of this study is considered to be novel in reservoir simulation that can improve predictions significantly.
