With about 90% of Saskatchewan's original heavy oil in place remaining in the ground, there is excellent potential for the application of enhanced oil recovery (EOR) methods and new technologies. The goal of the study discussed in this paper was to investigate if a new proposed process – coupling CO2 and polymer injection – can increase EOR performance for heavy oil reservoirs. The oil recovery performance of three EOR modes [water-alternating-gas (CO2 WAG) injection, polymer-alone flood, and coupled CO2 and polymer injection was compared in laboratory-scale linear coreflood tests in waterflooded cores. The immiscible CO2 WAG process recovered 15.3% original oil in place (OOIP) with 6.16 MSCF/stb gas utilization. Under a controlled maximum pressure drop across the core, the polymer-alone (0.4 wt%) flood produced an additional 12.93% OOIP above the initial waterflood recovery. However, the coupled CO2 and polymer injection process – using a polymer concentration of only 0.2 wt% – gave better recovery efficiency – 18.7% OOIP – than the polymer-alone flood. Moreover, it had much better gas utilization than the CO2 WAG run, consuming only 2.0 MSCF/stb, or one-third of the amount of CO2 used in that run – to recover the same amount of oil. This performance comparison demonstrates two of the biggest advantages of coupled CO2 and polymer injection: it can effectively reduce the pressure drop across the core and obtain very encouraging recovery if the optimal polymer concentration is added to the water.
The production of heavy oil accounts for more than 50% of Saskatchewan's total crude oil production.[1] However, currently only about 10% of the province's estimated 3.1 billion cubic meters (19.5 billion barrels) of heavy oil originally in place is recoverable based on current and expected conditions. With about 90% of the original heavy oil in place remaining in the ground, there is excellent potential for the application of enhanced oil recovery methods and new technologies. The benefits are readily apparent: if the EOR technologies can be developed to recover another 10% to 15% of the in-place resources, an additional 310?106 m3 to 465?106 m3 would be added to Saskatchewan's oil reserves.
Most of Saskatchewan's heavy oil deposits are described as lying in the " heavy oil belt", which extends from the Alberta border well into Saskatchewan (100–120 km). However, these heavy oil belts are deposited in a series of thinner blanket and channel sands at shallow depths and typically low reservoir pressures. They are not suitable for thermal recovery processes or for miscible gas injection, since miscibility between the oil and injected solvent gases, such as CO2, cannot be achieved under reservoir conditions; In addition, heavy oil production is constrained by very high oil viscosity, unconsolidated sand, and bottomwater, which all present special technical challenges.
Recently, immiscible CO2 flooding has generated interest as a method of enhanced heavy oil recovery. However, the very unfavourable viscosity ratio of CO2 to heavy oils leads to a combination of gravity override and CO2 fingering through more permeable zones, leading to early gas breakthrough and, ultimately, less oil being recovered.
