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An alternate injection of solvent and hot water/steam called Steam-Over-Solvent injection in Facture Reservoirs (SOS-FR) has been recently suggested and tested by our research group. In this process, most oil is produced during the solvent phase and then hot water/steam phase is assigned, mainly to retrieve the solvent. Oil recovery during this phase is typically low due to limited thermal expansion in the case of oil-wet matrix, and because capillary imbibition and gravity drainage driven by viscosity reduction do not have a significant contribution to the recovery. Wettability alteration toward more water-wet state will, however, enhance these mechanisms.Based on these facts, different wettability alteration agents were tested including cationic and anionic surfactants, ionic liquids, nano-fluids, high pH solutions, and low salinity water. The potential of these materials to modify the wettability of aged sandstone and limestone samples was evaluated using imbibition tests.Berea sandstone (aged to be oil-wet) and Indiana limestone samples were saturated with heavy oil (3, 600 cp). After the wettability modification was confirmed using different tests, the SOS-FR method was applied. The process was initiated by soaking cores into solvent (heptane or diluent oil) and the oil recovery was estimated using refractive index measurements. Then, two different experimental schemes were followed. In this first scheme, different brines were used and the oil production readings were taken periodically. These experiments will yield additional oil recovery (and solvent retrieval) by capillary imbibition and enhance gravity drainage if the wettability alteration due to solvent effect in the previous phase and chemical injected in the subsequent phase was achieved. In the second scheme, the heptane was retrieved first by hot-water exposure and the capillary imbibition tests were performed to test the selected chemical additive solutions as the wettability alteration agents.After conducting a total of 28 experiments, the most promising wettability alteration agents were marked and optimal application conditions (i.e., temperatures, injection sequence) were identified.

This study investigates the applicability of the modified version of the previously proposed SOS-FR (steam-oversolvent injection in fractured reservoir) method to recover bitumen from the Grosmont formation in Canada. Three phases were applied on a total of 13 preserved core samples. In Phase 1, the cores taken from three different parts of the Grosmont formation were soaked in a liquid solvent (heptane or distillate) at ambient conditions. The objective of the first phase was to reduce the viscosity of the bitumen in preparation for the second phase which is wettability alteration. In Phase 2, we soaked the samples in water with chemicals. Wettability modifiers tested include high pH solution, cationic surfactants, and ionic liquids because the screening process indicated they are the most useful wettability alteration chemicals for oil-wet carbonates. One of the key benefits of the ionic liquids is that they are environmentally friendly as they are chemically stable with low level of toxicity and flammabiliy. They can also be customized for particular rock/fluid system. On the other hand, pH solutions are economically attractive, in comparison with other wettability modifiers. Finally, Phase 3 was applied by increasing temperature to the bubble point of the solvent to mimic hot-water injection with chemicals. Each phase was analyzed in terms of ultimate oil recovery (and wettability alteration), time to reach this amount, the most suitable wettability alteration chemicals, and soaking times needed. The results revealed that the solvent phase not only affects the bitumen properties, but also changes Grosmont rock characteristics significantly. Wettability alteration of the fractured Grosmont reservoir was observed to be critical for additional oil recovery as well as for solvent retrieval. Specific high pH solution efficiently altered wettability and helped to recover considerable amount of bitumen/solvent mixture fairly quick showing a potential as a low cost chemical to recover bitumen. A discussion about the optimization of the process in terms of the solvent soaking period, wettability alteration chemicals, and the effect of temperature was also included.

Sole injection of steam or solvent into heterogeneous reservoirs usually yields an inefficient recovery performance. The SOS-FR (Steam-Over-Solvent Injection in Fractured Reservoirs) method was suggested as a solution to improve the efficiency of heavy-oil/bitumen recovery from fractured carbonates and oil sands reservoirs after cold production (Al-Bahlani and Babadagli 2008). The method consists of three phases: Phase (1): Steam is injected at low temperatures to heat the matrix and condition the oil for subsequent solvent injection; Phase (2): solvent injection to dilute matrix oil by diffusion and enhance gravity drainage recovery rate, and; Phase (3): low temperature (around the boiling point of solvent) steam injection to retrieve the solvent diffused into matrix.Previously, we focused on the effectiveness of Phases (1) and (2) of the method (Al-Bahlani and Babadagli 2009a-b) and observed very positive responses at the field scale (Al-Bahlani and Babadagli 2010) with high ultimate recoveries. The efficiency of this process, however, is purely determined by the amount of solvent retrieved at the end of the process. This paper, therefore, focuses on Phase (3), which is done mainly for solvent retrieval.About twelve static core experiments were performed on water and oil-wet sandstones. After saturating the rock samples with different heavy-oils, they were immersed into different liquid solvents-hexane, heptane, decane, and diluent oil. Once the ultimate recovery was achieved by diffusion and gravity drainage [Phase (2)], the samples were exposed to different temperature hot-water [Phase (3)] and the amount of solvent retrieved was measured through volumetric and weight measurements, as well as refractometer readings. The retrieval of solvent diffused into matrix was mainly due to two reasons: (1) Evaporation of solvent at elevated temperature, and (2) imbibition of hot-water into rock (if oil-wet samples become more water-wet during Phase (2).The amount of solvent retrieved through these processes were determined and the efficiencies were analyzed for different parameters including rock wettability, solvent type, solvent-soaking period, different combinations of steam-solvent cycle, and temperature applied.

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