Hydrocarbon solvent-based enhanced oil recovery techniques, such as cyclic solvent injection (CSI) and vapor extraction (VAPEX), have shown great potential to recover heavy oil reserves. But VAPEX suffers from low production rates because of the slow mass transfer and inefficient gravity drainage. CSI benefits from solution gas drive and foamy-oil flow; however, solvent gas release would cause the viscosity of the diluted oil to re-increase to slow down the oil flow. In addition, the oil rate of CSI might be uneconomical due to the long no-production injection/soaking period.
The UR team proposes a new process, named foamy-oil assisted VAPEX, to enhance the heavy oil recovery. This process applies the same production mode as a traditional VAPEX except the model pressure is reduced cyclically to induce foamy-oil flow.
In the new process, a vaporized solvent near its dew point is continuously injected into wells in the reservoir to maintain reservoir pressure and also supply extra gas drive to flush the now diluted oil out through an injector that is located on the top of the reservoir.
The producer wells are located at the bottom of the reservoir and are operated in a shut-in/open cyclic way. Essentially the reservoir gets pressurized and depressurized repeatedly. A series of experiments have been conducted to evaluate the CPCSI performance.
The recovery factors (RFs) are up to 85% of original oil in place (OOIP) in 1-D tests, and the RF is improved by 11% by using the 2-D lateral CPCSI, compared with the traditional 2-D lateral VAPEX. Well configurations and the producer shut-in/open scenarios are key optimization factors that affect the CPCSI performance. Experimental results show that the foamy oil flow and solvent trap are the two major enhanced heavy oil recovery mechanisms for enhancing the oil production rate during the production period. In comparison with continuous injection process, such as vapor extraction and cyclic injection process, such as cyclic solvent injection, CPCSI offers free gas driving, and the reservoir pressure is maintained during the producer-opening period so that the diluted oil viscosity is kept low.
Note the research is directed to heavy, or quite thick oil. Canada has massive untapped heavy oil and bitumen resources, much of it located in Western Canadian Sedimentary Basin. Heavy oil and natural bitumen are oils set apart by their high viscosity (resistance to flow) and high density (low API gravity).
A number of in-situ thermal methods, such as steam flooding, cyclic steam stimulation and steam-assisted gravity drainage, have been used to attempt to reduce the heavy hydrocarbon viscosity to enable production.
But for reservoirs with thin net-pay – the thickness of the zone in which the oil or bitumen resides or in the presence of a bottom water zone and/or with high water saturation in the pay zone, these thermal methods tend to be neither effective nor economical due to significant heat loss and large heating and water source requirements.
The CPCSI process uses a vaporized petroleum solvent that doesn’t mix with water. Propane is used to recover a heavy oil sample with a viscosity of 5,875 cP. For VAPEX, model pressure is kept at ~800 kPa. For foamy-oil assisted VAPEX, pressure control in each cycle consists of two periods: a constant pressure period and a pressure reduction period.
Results show that a strong foamy-oil flow can be induced through a pressure drawdown, which forms a foamy-oil zone. The foamy-oil flow pushes the solvent-diluted heavy oil inward the solvent chamber, which not only increases the oil production, but also helps solvent to contact the fresh heavy oil and accelerate the mass-transfer process. In the foamy-oil assisted VAPEX, oil that could not be produced in a traditional VAPEX by the gradititional force could be recovered in the foamy-oil assisted VAPEX process by a foamy-oil flow. Compared with a traditional VAPEX, foamy-oil assisted VAPEX can increase the oil production rate by 68.5 % and the final recover factor by 20.4%.
Hmm, the information is on the net, curiously without a press release from the university, with the research paper behind pay walls. Not many scientific papers get published multiple times, so this idea must have legs.
When you look at the map above, and consider the area involved both Canadian and U.S., the potential oil reserves to be added will be substantial. And most of it is already found with infrastructure in place.