The recovery of 1,600,000 cp bitumen from very heterogeneous carbonate reservoirs in the Grosmont unit in Albert is a great challenge. Steam injection alone may not be efficient due to the heterogeneous nature of the reservoir caused by natural fractures at different scales. Recent cold solvent studies showed limited recovery because of low diffusion coefficient and by-passing matrix oil. The hybrid use of steam and solvent could be an option to overcome some of these challenges. We adapted the previously introduced SOS-FR (Steam-Over-Solvent Injection in Fractured Reservoirs) method and conducted twelve experiments using preserved core samples from the Grosmont formation. The temperature used can be qualified as hot water injection thereby reducing the cost of heating the reservoir.

The method applied in this study is based on soaking rather than continuous injection. The samples were immersed in hot water (90 °C) first to mimic low temperature pre-steaming to condition the reservoir for solvent injection. This was followed by a solvent soaking period under varying conditions (duration, solvent type, etc.). Heptane and the distillate obtained from a heavy oil upgrading facility were used as solvents. Finally, the core samples were soaked in hot water again. Oil recoveries varied between 40% and 90% OOIP with a mean value of 68%. Asphaltene precipitation as a percentage of OOIP was measured between 6.5wt% and 33wt%. The oil recovery and asphaltene precipitation depended on the solvent type, the solvent exposure duration, the position of matrix rock (horizontal or vertical), and the duration and number of solvent/hot water cycles. Most importantly, the last phase (hot water immersion) yielded substantial recovery of solvent diffused into matrix oil by applying a temperature value close to the boiling point of the solvent. The solvent retrieval was extremely fast and varied between 62% and 82% of the solvent diffused into the core during solvent exposure.

Experimental observations look promising for further applications as indicated by the high recovery values. The important aspects are that the solvent from readily available distillates used for transportation of heavy oil are very responsive and the temperature requirement for final hot water injection applied to retrieve solvent was less than 100 °C. Solvent retrieval was extremely quick and reasonably high which is more likely to make the process economic.

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