Effect of Dead-Oil Viscosity and Injected-Solvent Type on SVX Process Performance

Abstract

Summary This work presents experimental results of four 3D-physical-model experiments that were performed to evaluate the dependence of the solvent-vapour-extraction (SVX) recovery process performance on initial dead-oil viscosity and injected-solvent-mixture composition. 0 Model excavation studies were also performed to approximate the solvent movement in the physical model and to map out the residual oil saturation and precipitated asphaltenes. The field-scale application and optimization of SVX processes requires that relationships be established among oil-production rates, solvent usage, and important process parameters (e.g., matrix permeability, initial dead-oil viscosity, solvent-mixture composition, and solvent usage). This work has attempted to generate such relationships for the two most promising mixed-solvent systems being considered for use in heavy-oil reservoirs. The analysis of the experimental results revealed that the initial dead-oil viscosity had a significant effect on the SVX performance. Higher oil-production rates were achieved with the lower-viscosity oils for both injected-solvent-mixture types, with a more-pronounced effect observed when using the CO2/C3 solvent mixture. The results also showed that the CO2/C3 mixture resulted in earlier solvent breakthrough and initial oil production, reduced solvent-makeup requirements (i.e., better solvent recycle stream), and reduced solvent retention in the model/reservoir, as compared with the C1/C3 solvent mixture. The residual-oil-saturation mapping showed that the CO2/C3 mixture led to comparatively lower values in the drained regions and a higher amount of precipitated asphaltenes remaining in the model, although there was evidence of some precipitated asphaltenes close to both the injection and production wells in all four experiments, regardless of the solvent-mixture type. Finally, this mapping also indicated that the solvent/oil interfaces and solvent chambers were more uniform and predictable for the CO2/C3 solvent-mixture injection.