Novel fluorinated surfactants for enhanced oil recovery in carbonate reservoirs

Novel surfactant-polymer (SP) formulations containing fluorinated amphoteric surfactant (surfactant-A) and fluorinated anionic surfactant (surfactant-B) with partially hydrolyzed polyacrylamide (HPAM) were evaluated for enhanced oil recovery applications in carbonate reservoirs. Thermal stability, rheological properties, interfacial tension, and adsorption on the mineral surface were measured. The effects of the surfactant type, surfactant concentration, temperature, and salinity on the rheological properties of the SP systems were examined. Both surfactants were found to be thermally stable at a high temperature (90 degrees C). Surfactant-B decreased the viscosity and the storage modulus of the HPAM. Surfactant-A had no influence on the rheological properties of the HPAM. Surfactant-A showed complete solubility and thermal stability in seawater at 90 degrees C. Only surfactant-A was used in adsorption, interfacial tension, and core flooding experiments, since surfactant-B was not completely soluble in seawater and therefore was limited to deionized water. A decrease in oil/water interfacial tension (IFT) of almost one order of magnitude was observed when adding surfactant-A. However, betaine-based co-surfactant reduced the IFT to 10(-3)mN/m. An adsorption isotherm showed that the maximum adsorption of surfactant-A was 1mg per g of rock. Core flooding experiments showed 42% additional oil recovery using 2.5g/L (2500ppm) HPAM and 0.001g/g (0.1mass%) amphoteric surfactant at 90 degrees C.