LAUSR

Abstract Numerous Alkali/Surfactant/Polymer flooding (ASP) projects have been developed worldwide. Nevertheless, some disadvantages have limited the success of ASP during the execution in field, such as injection lines scaling and strong emulsification of the produced fluids. Commonly, appropriate formulations for particular reservoir conditions are selected after a series of evaluation steps. These includes tests of surfactants, polymers and commercially available alkali, based on the reservoir temperature, reservoir salinity, reservoir water pH, rock permeability, formation type and adsorption of the surfactant on the matrix rock, to obtain the highest oil recovery at the lowest cost. As part of the different strategies adopted for increasing the oil recovery factor, San Francisco oil field, Huila Colombia, was selected in 2012 for ASP flooding application at pilot scale. After two years of injection, ASP effluents affected considerably the quality of water and its treatment for reinjection. The present work focuses on the compositional study of the production effluents obtained after ASP flooding. A detailed analysis using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) allowed disclosing the role of natural organic acids on reducing the interfacial tension which in turn entailed highly stable microemulsions. Together with the added surfactant, naphthenic acids (because of the alkaline pH) prompts the formation of these thermodynamically stable oil in water systems. A test using an acid free oil proved that the formation of microemulsions strongly depends on naphthenic acids presence. Additional tests using oils with different acidity showed the dependence on the naphthenics acids structure over the emulsion stability. The results obtained in this study stands out FT-ICR MS as a prominent tool on understanding breaking and/or clarifying treatment processes from a molecular level point of view and thus, could help on proposing a correct and cost effective water treatment.