Solvent vapour extraction (SVX) processes offer an attractive alternative to thermal recovery processes, being less energy intensive; and are more suitable for thinner, partially depleted reservoirs. A typical SVX process uses solvent injection to dilute the heavy oil by reducing its viscosity, allowing it to be mobilized for production. During this process the injection of hydrocarbon solvents results in partial deasphalting of the heavy oil, thus further reducing its viscosity and enhancing the process performance.
This work examined the formation and growth of solvent chambers in laterally and vertically spaced horizontal injector/producer well pairs in porous media with five different permeabilities and three different solvent vapour qualities. Consolidation of the porous media due to asphaltene precipitation was also analyzed. Thermal imaging and model excavation studies were performed to investigate the formation and growth of solvent chambers for seven different experiments conducted on a large 3D physical model apparatus.
The important findings from this study are as follows: During solvent injection, one or more solvent fingers develop between the injector and producer. The dominant solvent finger becomes a conduit that grows into a solvent chamber connected to the injection well in the upper portion of the reservoir, and develops into an oil drainage conduit connected to the production well in the lower portion of the reservoir. Solvent dispersion layers are located on the margins of both the solvent chambers and the oil drainage conduits. The location and development of these non-uniform solvent chambers and oil drainage conduits are unpredictable, and the oil drainage conduits do not grow significantly in diameter once connected to the production wellbore, limiting the wellbore inflow efficiency and conformity. Asphaltene precipitation and migration can aggravate this inflow problem, further reducing SVX process performance.
SVX performance can be improved by increasing the number and diameter of oil drainage connections between the solvent chamber and the production well, and by controlling the oil deasphalting process. This can be done by optimizing injection and production wellbore geometries, and by optimizing solvent injection rates and vapour quality.