Whereas polymer flooding is now a proven method for heavy oil reservoirs, the use of surfactants is reported only in a limited number of cases and mostly in combination with alkali (ASP) to benefit from in-situ generated soaps. Operational issues such as scale formation, corrosion or logistics difficulties are often encountered. The objective of this work was to assess for the feasibility of alkaline-free surfactant-polymer (SP) processes for heavy oil reservoirs. Three "pseudo-synthetic" sandstone cases have been investigated for SP formulation design and performance evaluation through coreflood tests:

  • 100 cP oil viscosity, 60°C, 800 mD and salinity 7.5 g/L TDS;

  • 1400 cP oil viscosity, 35°C, 2 D and salinity 20 g/L TDS;

  • 4500 cP oil viscosity, 50°C, 2-4 D and salinity 6.4 g/L TDS.

All experimental assays have been carried out on outcrop rock plugs but with dead oil samples from real reservoirs. SP formulations were successfully designed for the three cases with ultra-low IFT (<10−2 mN/m) at the target salinities and with good solubilities. For the 1400 and 4500 cP cases, SP tertiary oil recovery coreflood tests were carried out and led to high recoveries, namely above 90% of post-polymer flooding ROIP. For the 1400 cP case, a salinity gradient method was proven successful to mitigate adsorption. For the 100 cP case, injections at and below the optimal salinity were carried out with good results in both situations. To enable these experimental assays, new protocols had to be developed to contend with the specificities of heavy oils such as very long equilibrium times and difficulties to determine the oil production in corefloods. These exploratory investigations demonstrate that alkaline-free SP processes are feasible for heavy oil reservoirs and that field operations can be prepared using proper laboratory methods.

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