ASP flood of a viscous oil in a carbonate rock

• An ASP formulation was developed that gives ultralow IFT with a viscous oil.
• The alkali reduces anionic surfactant adsorption on dolomite without calcite precipitation.
• 93–95% of the viscous oil was recovered in core floods.

The goal of this work is to develop an alkaline–surfactant–polymer (ASP) formulation for a viscous oil (105 cP at the reservoir temperature) and compare secondary and tertiary ASP floods. Phase behavior studies were performed to find an ultralow interfacial tension (IFT) ASP formulation for the viscous oil. Static surfactant adsorption experiments were performed to compare the effectiveness of different alkalis in reducing adsorption. The surfactant formulation was tested with an outcrop vuggy dolomite core in both tertiary and secondary modes. Lab coreflood results were modeled in UTCHEM which used EQBATCH to model sodium metaborate geochemical reactions in a carbonate rock. Sodium carbonate and sodium metaborate were both found to be equally effective in reducing surfactant adsorption on crushed dolomite. Waterflood recovered about 47.8% of the oil in place and reduced the oil saturation to 43.8%. The tertiary surfactant flood increased the cumulative oil recovery to 92.7% whereby the oil saturation was reduced to 6.1%. The secondary surfactant flood was even more effective than the tertiary; the oil saturation was reduced to 3.1% and the oil recovery was 95.6% OOIP. Very low surfactant retention was observed in the ASP corefloods. UTCHEM simulations showed a reasonable match with the experimental results. Experimental data for surfactant phase behavior, polymer viscosity, and surfactant adsorption were critical in modeling the experimental results.