Although the previous static experiments provided critical information as to the existence of a critical temperature range that yields the maximum heavy-oil recovery during steam/solvent injection, dynamic experiment are needed to account for the relationship between the solvent introduced into the system and heavy-oil recovery.
We conducted a series of dynamic experiments in which liquid (heptane) solvent was injected into a heavy oil saturated rock matrix, surrounded by a fracture with and without pre-thermal injection. Water-wet rock matrix (sandstones) was saturated with heavy oil and placed inside a core holder. Next, the system was placed into an oven and maintained at constant temperature conditions. Then, either hot solvent (superheated to be in vapor phase) or cold solvent was introduced into the system through the fracture at a constant rate. Pressure and temperature was continuously monitored along the core and the properties of oil and liquid condensate from gas produced were measured and analyzed. This scheme was repeated for a wide range of temperature conditions.
The first requirement for a successful application is that the solvent should diffuse into matrix effectively before it breaks through and improves gravity drainage of oil by dilution. The second requirement is solvent retrieval. The retrieval of the solvent during solvent injection phase and post-thermal method (steam or hot-water) injection performed at the near-boiling point temperature of the solvent was monitored. Our results and observations indicate that there exists a critical temperature and injection rate that yields a maximized oil recovery and solvent retrieval.