Certain Athabasca reservoirs have low pressures because they have been depleted due to production of over-laying gas. Other reservoirs are naturally occurring low-pressure shallow bitumen reservoirs. Hence, there is a need to develop or investigate recovery processes under which such low-pressure reservoirs can be developed. As a result of this, experiments were initiated to extend the Expanding Solvent-SAGD (ESSAGD) process application to low-pressure Athabasca reservoirs and in order to evaluate oil recovery from such reservoirs. The goal of these experiments is to develop lowpressure ES-SAGD process with better performance than, or comparable performance to, that of high-pressure SAGD process.
This paper describes five sets of laboratory experiments examining recovery processes, which include low-pressure (500 kPag+/- 50 kPag) SAGD experiment, propane-SAGD experiment and multi-component solvent ES-SAGD (at low and high concentrations) experiments; and a high-pressure (2100 kPag +/- 50 kPag) SAGD experiment. The results of these experiments are presented and analyzed in order to evaluate the performance of low-pressure ES-SAGD in comparison to SAGD (at low and high pressure) and propane-SAGD at low-pressure. The processes were assessed for recovery; recovery time; heat loss; steam chamber growth; and energy efficiency.
The principal conclusion is that the low-pressure multicomponent solvent ES-SAGD at the right concentration (mostly at low concentration) is fairly competitive with SAGD at high pressure. The energy consumptions per oil recovered for lowpressure multi-component ES-SAGD experiments are much lower than the low-pressure and high-pressure SAGD tests. The propane-SAGD test recovery is very low, even at higher energy consumption, than that of ES-SAGD experiment at low concentration. The work presented in this paper shows that the application of multi-component solvent ES-SAGD process in the field at low-pressure is a practical option. It also shows that bitumen/heavy oil reservoirs that would have remained untapped due to low-pressure reservoirs could be produced at lower energy consumption per oil recovered if a low-pressure ES-SAGD process at low concentration of the diluents is employed in the recovery of the oil.
Certain Athabasca reservoirs have low pressures because they have been depleted due to production of over-laying gas. Other reservoirs are naturally occurring low-pressure shallow bitumen reservoirs. The application of Expanding Solvent-SAGD (ESSAGD) (1–2) to these low-pressure reservoirs has been a major area of attention at Alberta Research Council (ARC) in recent years. As a result of this, experiments were initiated to extend ES-SAGD application to low-pressure Athabasca reservoirs. The goal is to develop low-pressure ES-SAGD process with better performance than, or comparable performance to, that of high-pressure SAGD process and extend ES-SAGD process application to gas-over-bitumen reservoirs and naturally occurring low-pressure reservoirs.
In this paper, four low-pressure experiments and one highpressure experiment conducted in a 2-D experimental facility at the Alberta Research Council are presented and analyzed in order to evaluate the performance of ES-SAGD at low pressure. The low-pressure experiments are SAGD, propane-SAGD, high-concentration multi-component solvent ES-SAGD and low-concentration multi-component solvent ES-SAGD experiments. The low and high concentrations refer to the concentrations of the diluent in the ES-SAGD experiments.
