Hot Solvent Injection for Heavy Oil/Bitumen Recovery from Fractured Reservoirs: An Experimental Approach To Determine Optimal Application Conditions

We conducted a series of dynamic experiments in which liquid solvent (heptane) was injected into heavy-oil saturated artificially fractured Berea sandstone samples with and without prethermal injection. To account for the effect of wettability on the process, experiments were repeated on the samples exposed to a wettability alteration (more oil-wet) process. Cores were saturated with heavy crude oil and placed inside a rubber sleeve. Next, the system was placed into an oven and maintained under constant temperature conditions. Then, either hot solvent (superheated to be in the vapor phase) or cold solvent was introduced into the system through the fracture at a constant rate. Pressure and temperature was continuously monitored at the inlet and center of the core. Properties of the oil and liquid condensate from the gas produced were measured and analyzed. This scheme was repeated for a wide range of temperature conditions. The retrieval of the solvent during the solvent injection phase and post-thermal method (steam or hot-water) injection performed for a wide range of temperature was monitored. Our results and observations indicate that the first requirement for a successful application is an effective solvent diffusion into matrix before it breaks through and improves the gravity drainage of oil by dilution. The second requirement is solvent retrieval. We also observed that a critical temperature and injection rate exists that yields a maximized oil recovery and solvent retrieval.