Heavy oil recovery from matrix blocks of Indiana limestone and Silurian dolomite core samples was studied using a cylindrical core holder set-up. Fractures in the system were represented by a gap between the core sample and core holder wall. Core samples and fractures were respectively saturated with heavy oil and gas. Oil recovery experiments were conducted in batch-mode using two different gases, nitrogen and carbon dioxide, at 1000 psi and various temperatures (200, 250, and 300 °C). N2 was employed as an inert gas to study the effect of temperature in oil production from the cores without affecting its chemical properties. Consequently, CO2 was used to investigate the role of mass transfer between matrix and fracture fluids in oil recovery.
The produced oil from the matrix was collected and the recovery factor for each experiment was calculated. Moreover, the remaining oil in the core was extracted. Viscosity determinations and simulated distillations of the two samples, produced oil and remained oil in the core, were carried out in order to assess oil quality distribution.
Experimental results revealed that with immiscible gas injection at high temperatures oil segregation occurred in the porous media. Consequently, lighter components of oil were produced while the heavier ones were left behind inside the matrix. Results also demonstrated a relationship between the amount of oil produced and the oil segregation in the porous media.
This research provides a systematic analysis to investigate the main recovery mechanisms from carbonate matrix blocks under various hot gas injection scenarios, which is of great interest to determine the most appropriate enhanced recovery method to be applied for heavy oil production from naturally fractured reservoirs.