Solvent- Steam Assisted Gravity Drainage (S-SAGD) processes for bitumen extraction are proposed to reduce the environmental impact of steam injection. S-SAGD processes require more research due to the unknowns of solvent-bitumen interaction and the desire to reduce the cost of steam and solvent utilized. This study investigates propane-SAGD (P-SAGD) and propane-steam flooding (P-SF) performance for the recovery of a Canadian bitumen from Alberta with 9.6 API gravity, 290,500 cP viscosity (at 25 °C), and 21.7 wt% asphaltenes (n-pentane insoluble) content. Three two-dimensional SAGD experiments (one SAGD and two P-SAGD at two different propane doses) and three one-dimensional flooding experiments (propane, steam, and propane-steam) were conducted. By comparing 2D experiments with 1D, we were able to analyze the effect of continuous steam flow and steam chamber development on process performance in microscopic scale. Water and asphaltenes contents of produced oil were measured. It has been observed that the steam chamber development with propane coinjection enhanced the oil production, however, led to delay in oil production compared to the steam flooding case. Thus, we also tested first steam injection until achieving the communication between the injector and producer in SAGD configuration and then, switching to steam-propane coinjection. After allowing the steam-bitumen interaction first, propane injection did not result in severe water-in-oil emulsion formation. Moreover, lesser permeability reduction due to asphaltenes deposition was observed. The application of propane-SAGD as follow up to SAGD improved the process by the mobilization of trapped residual oil and enhanced the quality of produced oil by minimizing the formation of water-in-oil emulsion.
The objective of this paper is to enhance the produced oil quality during solvent-steam flooding processes by using asphaltenes precipitants and environmentally friendly solvents as injection fluid. This way, it is aimed to increase the asphaltene deposition tendency and decrease the emulsion formation severity. Eight one-dimensional core flood experiments were conducted; one steam flooding, three solvent flooding, and four solvent-steam flooding. Five different solvents were tested; propane, n-hexane, toluene, Benzoyl peroxide (BP), and a plant-based environmentally friendly solvent (MS). Solvent and water injection, oil and water production, and temperature along the core flood were continuously measured during each experiment. Both produced oil and residual oil samples were further analyzed to investigate the quality of produced oil samples and the amount of asphaltenes deposited on spent rock. An ASTM method which uses n-pentane was implemented to separate asphaltenes from both produced and residual oil samples. The water content of produced and residual oil samples was determined through thermogravimetric analysis (TGA) and the water-in-oil emulsion content of produced oil samples was visualized with an optical microscope. To understand the impact of each SARA (Saturates, Aromatics, Resins, and Asphaltenes) fractions on produced oil quality during solvent-steam processes, every fraction was exposed to liquid or vapor water and examined under a microscope. It has been observed that stability of asphaltenes and emulsions varies in the presence of vapor or liquid water. Aromatics and Resins fractions are the main contributors of water-in-oil emulsion formation, and emulsion formation is enhanced with the addition of asphaltenes. Vapor-water (steam) promotes the formation of more severe emulsions than liquid-water. Hence, the emulsion formation mechanism was predicted to start with a foam-formation step in where the vapor steam diffuses into the liquid crude before condensing to form liquid water droplets, and then, forming an emulsion at lower temperatures. Since asphaltenes insoluble solvents were used, diffusion of steam occurs mostly in deasphalted oil and mainly in aromatics and resins.
Steam flooding is the most widely used thermal enhance oil recovery (EOR) process to recover bitumen and heavy oil. This process has been proven to be reliable, thus, establishing itself as a favorite among other thermal EORs. However, the excessive water usage to generate steam causes environmental concerns such as air and water pollution. Thus, a noble idea to reduce the sole dependency on steam alone is to co-inject solvent with steam. Solvent will aid the oil recovery process by improving miscibility aside from the oil displacement mechanisms from steam itself. Three core flooding experiments were conducted on a heavy oil sample from Texas; namely, steam flooding (E1), CO2 -steam flooding (E2), and CO2 - MS- steam flooding (E3). MS is a corn based environmentally friendly solvent which is tested for the first time for heavy oil extraction via solvent-steam injection process. Because CO2 is known as asphaltene insoluble solvent, asphaltene precipitation was also investigated on spent rock samples to determine the formation damage occurring during the process. An ASTM method was used to determine the amount of asphaltenes in initial oil sample, on produced oil samples, and on residual oil samples. Another flow assurance problem is emulsion formation which occurs widely in any steam processes. Hence, the emulsions formed during solvent-steam and steam experiments and the role of asphaltenes on emulsion formation are investigated. It has been observed that CO2 enhances the asphaltene precipitation and results in consolidation of core samples which reduced significantly the oil production. The use of asphaltene insoluble solvent CO2 with an asphaltene soluble solvent (MS) enhanced the oil production, increased the sweep efficiency and decreased the water-in-oil formation. With this study for the first time asphaltene soluble and insoluble solvents co-injected together with steam to recover a heavy oil from Texas. We also analyzed the oil displacement mechanism through asphaltene precipitation and emulsion formation.
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