While chemical floods have proven technically successful, the high cost of chemicals makes it challenging to develop a cost-effective tertiary process. If high interfacial tension (IFT) exists between the oil and water phases, the resulting capillary forces will resist externally applied viscous forces. This could cause the injected water and chemicals to bypass the residual oil and go to waste.
The experimental studies presented here include reservoir fluid characterization, IFT measurements, and coreflood tests, all critical elements in designing a costeffective ASP (alkaline/surfactant/polymer) injection strategy. Coreflood tests used either sandpacks or composite reservoir cores with a selected medium crude oil. Injected surfactant concentration, slug size, chasing fluid, and residual oil saturation were the varied parameters. The optimal surfactant concentration of 0.15 wt% and slug size of 0.5 pore volume (PV) obtained relatively high oil recovery while maintaining a favorably high displacement efficiency ratio. Incremental recovery was 23–41% initial oil in place (IOIP) in sandpack tests and about 16% IOIP with reservoir cores. Overall, these coreflood results indicate that ASP flooding is a suitable enhanced oil recovery method for medium oil if the right chemical concentration and slug size are selected.
The use of ASP flooding to recover oil left behind by waterflooding has become more common in recent years. Several significant developments have made ASP flooding a viable option for field enhanced oil recovery (EOR) projects and more attractive than polymer or micellar/polymer flooding. First, because world oil consumption continues to grow while production in many mature fields continues to decline, oil prices are predicted to stabilize above US$20/bbl. Second, newly developed cheaper surfactants have reduced the cost of EOR formulations by 40 to 60%, while maintaining the same high oil recoveries obtained using more expensive surfactants. The incremental cost per barrel of oil produced has been reduced to a reasonable level, around US$1.44 to $5.83.1 Third, chemical flooding can be evaluated in the oilfield faster and more economically than in the past using the single-well EOR pilot test and field-scale numerical simulations. Fourth, waterfloods in most mature reservoirs have experienced early water breakthrough and have reached their economic limit; therefore, oil companies have to consider applying new EOR technologies to increase recovery factors in such fields.
The proven medium oil resource in southwest Saskatchewan, estimated at 3.1 billion barrels, is located in reservoirs characterized by thin pay (two to eight meters in thickness) and shaly sand. The estimated oil recovery by primary and secondary methods from these reservoirs is about 25% IOIP. 2 There has been little development of medium oil reservoirs in southwest Saskatchewan by enhanced oil recovery technologies, and conventional methods are nearing their economic limit.
The Saskatchewan Research Council (SRC) has conducted extensive studies to develop ASP flooding for a selected reservoir"Instow"with reserves of about 22.1?106 m3 (140 million barrels) of medium oil originally in place. Instow field is located in ranges 18 and 19 of townships 9 and 10 in southwest Saskatchewan.
