Abstract

Steam Assisted Gravity Drainage (SAGD) is a proven enhanced oil recovery technique for oil sand extraction. However, the environmental and economic challenges associated with steam generation limit the application of this technology. To address these issues, we investigated the effectiveness of Expanding Solvent SAGD (ES-SAGD) over base SAGD on a bitumen sample (8.8 °API). Experimental studies are conducted with a two-dimensional physical model. Different strategies for solvent injection are tested (co-injection and cyclic injection) to examine the deposition of polar fractions of the bitumen on porous media or producing polar fractions with non-polar ones. To investigate the level of oil upgrading while toluene is used as asphaltene soluble solvent, n-hexane was selected as asphaltene insoluble. Steam chamber development is monitored with temperature profiles from 47 separate positions. Steam oil ratios, solvent oil ratios, and the level of oil upgrading in terms of viscosity reduction and API gravity improvement are evaluated together. Environmental footprints of SAGD with ES-SAGD are discussed in terms of solvent toxicity, total produced greenhouse gases, and asphaltene precipitation with FTIR analysis on postmortem samples. Furthermore, the energy intensity of the processes is assessed by considering steam generation and solvent costs. This study reveals that co-injection of hydrocarbon solvents with steam enhances the steam chamber development with higher oil production rate. Moreover, ES-SAGD results in recovery of more upgraded oil and has less environment impact. We observe that the selection of the solvent type and injection strategy are the most crucial parameters for the design of hybrid SAGD process and solvent cost can be minimized by using the recycled solvent for continuous injection of solvents. High energy consumption for steam generation during SAGD process can be reduced by co-injection with steam proper solvent type at proper injection strategy. This experimental study reveals that ES-SAGD process has environmental and economic benefits over base SAGD. However, some solvents can cause undesirable effects due to the asphaltene destabilization and precipitation in production or transportation lines. Results of this work can be used to better address solvent interaction with polar components during SAGD.

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