Light hydrocarbon solvent was used to produce bitumen from Cold Lake oilsand in three dimensional scaled physical modeling experiments. Injection ofthe gas was carried out through a horizontal well until the bottom holepressure was slightly above the saturation pressure at model temperature.Production of diluted bitumen followed the injection cycle through the samehorizontal well until pressure in the reservoir was depleted slightly below thesaturation pressure at model temperature. At that pressure liquid productionrates were very low. In some of the experiments with ethane gas, pressure inthe model varied between 3.2 and 4.0 MPa, which is near the Cold Lake reservoirpressure. This favorable physical property of ethane was offset by a smallerimprovement in product quality as compared to that from tests with propane.
The results of these experiments show that the production rate of bitumenassuming a gravity drainage drive mechanism with a single horizontal wellcyclic process was significantly higher than what could be expected from themolecular diffusion rate of solvent into the bitumen, indicating that othermechanisms, probably solvent dispersion or fingering, are important in the masstransfer of solvent into the bitumen. Reasonable efficiency and effectivenessof ethane as solvent were achieved, resulting in a small loss of solvent andlow solvent to bitumen replacement ratio in the experiments.
Based on the measurement of the residual oil saturation along the wellbore, full utilization of the horizontal well was not achieved in the model tests.Production enhancements would be expected if this technical deficiency could beovercome.
Half of the original bitumen in place in Imperial Oil's leases at Cold Lake, Alberta is located either in bottom water reservoirs or water sensitive sandswhich are not amenable to exploitation by steam based processes. A potentialalternative for these reservoirs is a solvent based process which has been thesubject of laboratory investigations by a number of researchers [1–9] in recentyears. The advantages of the solvent based processes are: little heat loss andlimited water handling, the disadvantage are: high solvent cost and inherentlylow production rate limited by mass transfer of the solvent into thebitumen.