This paper discusses the evolution of an Alkaline Surfactant Polymer (ASP) formulation for a challenging sandstone reservoir in North Kuwait. This is an on-shore reservoir, with no gas cap, featuring a moderately high residual oil saturation to waterflood of approximately 20-30%. Moreover, the reservoir has a light oil (API Gravity 30-35) with low Total Acid Number (TAN) and is undergoing a maturing waterflood – thus making it amenable to ASP implementation. However, the high reservoir temperature (90°C), in-situ brine salinity (>250,000 ppm) and divalent ion concentration (>20,000 ppm) place the reservoir at the upper threshold of ASP technology implementation.
In addition, the oil has a high emulsification tendency and was observed to form very stable brine-oil emulsions when sampled from the field. This was due to the high concentration of heavier components such as waxes, resins and asphaltenes, some of which are surface-active and tend to interfere with the action of synthetic surfactant at the oil-water interface making ASP formulation development for such oils very challenging. Furthermore, addition of polymer to improve the ASP/oil mobility ratio caused phase separation of the aqueous phase likely because the water-soluble polymer preferentially dissolves in brine while pushing out the hydrophobic surfactant. The methodology followed in this work was to select a surfactant with a high alkyl tail length to solubilize the heavier hydrocarbons in the oil, blend it with a more hydrophilic surfactant to increase the optimal salinity to match the target injection water salinity and overcome the surfactant phase separation issue when polymer was added to the formulation. The ASP formulation was successfully tested in the field in a Single Well Chemical Tracer Test (SWCTT) and was successful in reducing the remaining oil saturation from 0.24 ± 0.02 at the end of water flood to 0.06 ± 0.05 at the end of the chemical flood.