Light hydrocarbon solvent was used to produce bitumen from Cold Lake oil sand in three dimensional scaled physical modelling experiments. Injection of the gas was carried out through a horizontal well until the bottom hole pressure was slightly above the saturation pressure at model temperature. Production of diluted bitumen followed the injection cycle through the same horizontal well until pressure in the reservoir was depleted slightly below the saturation pressure at model temperature. At that pressure liquid production rates were very low. In some of the experiments with ethane gas, pressure in the model varied between 3.2 and 4.0 MPa, which is near the Cold Lake reservoir pressure. This favourable physical property of ethane was offset by a smaller improvement in product quality as compared to that from tests with propane. The results of these experiments show that the production rate of bitumen assuming a gravity drainage drive mechanism with a single horizontal well cyclic process was significantly higher than what could be expected from the molecular diffusion rate of solvent into the bitumen, indicating that other mechanisms, probably solvent dispersion or fingering, are important in the mass transfer of solvent into the bitumen. Reasonable efficiency and effectiveness of ethane as solvent were achieved, resulting in a small loss of solvent and low 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 be overcome. Introduction 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 sands which are not amenable to exploitation by steam based processes. A potential alternative for these reservoirs is a solvent based process which has been the subject of laboratory investigations by a number of researchers(l-9) in recent years. The advantages of the solvent based processes are: little heat loss and limited water handling; the disadvantages are: high solvent cost and inherently low production rate limited by mass transfer of the solvent into the bitumen. The recovery process utilizing light hydrocarbon gas was first investigated by Dunn et al.(1,2) on Athabasca oil sands and later by R.M. Butler(3–9) on heavy oil and Peace River bitumen in a two dimensional scaled physical model. In their investigations, both researchers modelled solvent assisted gravity drainage with a pair of horizontal injector and producer wells in much the same way as the Steam Assisted Gravity Drainage (SAGD) process. The present study applied the concept of cyclic stimulation with a solvent gas through a single horizontal well. Compared to the two well SAGD type configuration, the advantage of this process concept is the halving of well costs. As illustrated in Figure I, solvent gas is injected to the horizontal well until the bottom hole pressure exceeds the saturation pressure of the solvent (3.6 MPa for ethane at 13 °C).

In a three dimensional scaled physical modeling experiment, Cold Lake oil sand was subjected to cyclic stimulation with supercritical ethane through a single horizontal injector/producer well located at the base of the reservoir. Hot ethane gas was injected into the bottom of the formation until the bottle hole pressure reached slightly above the ethane supercritical pressure of 4.9 MPa. Production of diluted bitumen followed the injection cycle through the same horizontal well until pressure in the reservoir was depleted slightly below 4 MPa. At that pressure liquid production rates were very low During the experiment, temperature in the model varied considerably with the distance from the wellbore as well as with the number of stimulation cycles. Supercritical ethane enhanced the cyclic solvent gas process by improving the early production rate. As well there was an increase of recovery of solvent in the blowdown at the end of the experiment. Both are important factors for the process economics. Time animation of the temperature profile revealed that solvent gas preferentially invaded the region in close proximity to the production end of the horizontal well. The observation was consistent with the post test measurement of residual oil saturation in the model which showed that bitumen was preferentially depleted from that region. Evidently, full utilization of the horizontal well was not achieved in the experiment. Production enhancements would be expected if this technical deficiency could be overcome. Introduction The current in situ recovery process practiced at Cold Lake Alberta by Imperial Oil Resources Limited (IORL) uses high pressure steam to reduce bitumen viscosity and mobilize the oil. The process has been applied successfully for many years to produce bitumen from good quality sands from the thick Clearwater formation. However, only a small fraction of IORL's reserve holding at Cold Lake is in the good quality reservoir, with the rest categorized as either thin, shaley or bottom water reservoirs. P. 521

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