Experimental Investigation of Bitumen Recovery From Fractured Carbonates Using Hot Solvents

With the decrease in conventional oil and gas reserves throughout the world and an ever-increasing demand for fossil-fuel-based energy and resulting high oil prices, focus has been shifting to unconventional and heavy oil and bitumen. Grosmont carbonates in northern Alberta have been estimated to contain at least 300 billion bbl of heavy oil or bitumen. However, recovering this oil is extremely difficult because of the complexity associated with carbonate reservoirs in general (e.g., the Grosmont unit is known to possess a triple-porosity system of matrix, fractures, and vugs, on the basis of core studies). The second problem is the fluid itself, which is highly viscous bitumen that is immobile at reservoir conditions. To extract this bitumen from heterogeneous carbonate rock, both heat and dilution using solvents may be needed. This paper reports the results and analysis of hot-solvent experiments conducted on original Grosmont carbonate cores. Three experiments were conducted using propane and one using butane as solvent. After heating the entire system containing the core sample, solvent gas was injected. The rock was allowed to soak in the hot solvent for a long time. The experimental temperature and pressure were decided on the basis of the results of our earlier work that suggested they be slightly above the saturation line of the particular solvent. An attempt was made to keep the conditions close to the saturation conditions of the solvent being used to maximize the dilution and, hence, the recovery. The oil produced was analyzed for viscosity and asphaltene content. The results in terms of recovery, the degree of dilution, and upgrading achieved suggested that butane was a better solvent for this bitumen. Finally, the optimum conditions for operation of the hot-solvent process were verified for Grosmont carbonates.