Use of a small amount of solvent with steam has been shown to be effective for the recovery of very viscous oils. The mathematical treatment of such thermal-miscible recovery methods has been virtually nonexistent. This paper describes an experimental and theoretical investigation of miscible displacement under nonisothermal conditions, which serves to pave the way to studies of more complex systems.
The hot miscible floods were carried out in an adiabatic glass bead pack, displacing one hydrocarbon by a more viscous hydrocarbon, the latter being at an elevated temperature. As a result, dispersion of both mass and heat took place, and was determined by temperature and concentration measurements. The system was simulated by coupled convective-diffusion and thermal conduction-convection equations. The results of the numerical as well as an approximate analytical solution were compared with the experimentally observed behavior.
It would found that the recovery of the displaced hydrocarbon increased with the injection temperature up to a point, beyond which it decreased due to mobility ratio inversions, caused by the different viscosity-temperature relations of the two liquids. As a result, determination of the dispersion coefficient by the usual isothermal methods can be unreliable. On the other hand, the use of isothermally determined dispersion coefficients in the mathematical model did not yield a good match between the observed and calculated temperature and concentration profiles. A history match indicated a complex relationship between heat convection and dispersion of material. The calculated local mobility ratios showed a maxima and minima for any temperature profile. The numerical and experimental results point to the factors which should be considered in the choice of a solvent tor a thermal-miscible type oil recovery process.
Numerous experimental and theoretical studies have dealt with the displacement of one liquid by another miscible with it, under isothermal conditions. To date, an investigation of miscible displacement under nonisothermal conditions has been lacking. Such aprocess is of considerable interest at the present time, since many studies by Farouq Ali and Coworkers, as well as others, have employed solvents together with steam for the recovery of bitumen from the Athabasca oil sand. Apart from that. solvents have been employed in conjunction with hot water and steam for the recovery of moderately viscous oils, by Abbas Alikhan and Farouq Ali (1, 2). The rationale Ear the use of a solvent differs for the above situations. For example. in the case of an oil sand, containing a semi-solid hydrocarbon, the goal is to create an initial flow channel tor subsequent steam injection. In all ins~ances, the solvent is less viscous than the in-place oil, and consequently, the mobility ratio is greater than unity ("unfavourable"). The displacement would be unstable under such conditions,a problem which has so far defied a comprehensiveanalytical treatment even for simple systems.
The present study is a first attempt to examine miscible displacement under nonisothermal conditions, experimentally as well as theoretically.