Solvent retrieval and wettability alteration during heavy-oil and bitumen recovery by SOS-FR (steam-over-solvent injection in fractured reservoirs) method

Abstract

Water injection is inefficient to recover heavy oil from naturally fractured carbonate reservoirs mainly due to its oil-wet nature of the matrix. Solvent injection could be an option in this type of reservoir through dilution of oil and gravity drainage. This, however, will only be feasible if the injected solvent is retrieved back effectively. This thesis focuses on the two approaches that can be used to retrieve the solvent diffused into matrix: (1) Thermal method and (2) chemical methods. In the thermal method, steam or hot water is injected at or around the bubble temperature of the solvent. The solvent will then be retrieved by its vaporization, which was the base of a recent suggested method called steam over solvent injection in fractured reservoirs (SOS-FR) method (Al-Bahlani and Babadagli, 2008). An experimental setup that enables quantifying the retrieved solvent at the end this process was designed and then used to investigate the effect of different factors on the process. Then, an optimization study was performed to determine the optimal conditions for oil recovery and solvent retrieval during the SOS-FR method. Chemical methods rely on the possibility of altering the wettability of rock surfaces. This type of treatment is a new approach to develop heavy oil/bitumen containing oil-wet systems. After a critical review of the past literature in wettability alteration with a comprehensive analysis of materials/methods suggested for different types of reservoirs, selected chemicals were tested on heavy-oil saturated core samples pre-exposed to solvent. The chemicals tested include surfactants, high pH solutions, low/high salinity water, nanofluids, and ionic liquids. The key parameters to evaluate the efficiency of the examined recovery methods were oil recovery and solvent retrieval through enhanced capillary imbibition.