A Methodology for Screening Surfactants for Foam Enhanced Oil Recovery in an Oil-Wet Reservoir

A surfactant-screening methodology for foam enhanced oil recovery (EOR) is proposed that comprises both bulk-foam tests and foam flooding in model porous media. The initial foam screening (bulk-foam stability in test tubes) is aimed at quickly providing a qualitative indication of a surfactant's foaming potential as well as salinity and oil tolerance at reservoir temperature. Surfactant formulations passing these tests are tested further in a series of foamflooding experiments in model porous media (bead packs) under reservoir conditions (100-bar backpressure, at 55 degrees C) at 95% gas fraction, with and without crude oil (32 degrees API) present. The mobility-reduction factor (MRF) (i.e., ratio of pressure drop across the pack with foam compared with that for water) is a direct measure of foam strength in porous media. To investigate the effect of wett-ability, tests are performed in both strongly water-wet (glass beads) and oil-wet (polypropylene beads) porous media. The bulk-foam tests screened out most of the considered surfactants. Out of 31 surfactants tested, 26 precipitated in the highest-salinity brine (200,000 ppm). Also, the presence of crude oil resulted in foam collapse for most surfactants in the bulk tests. Surfactants that retained some foam stability in the presence of oil were carried forward to the porous-media tests. In our study, qualitative foam stability inferred from the bulk-foam-stability tests correlated well with the MRF in the water-wet bead packs. We found large variations in MRF comparing different surfactants; some have MRFs on the order of 10 and others are as high as 1,000. For all investigated surfactants, the presence of crude oil reduced MRF, but for some mobility reduction was still significant. The bulk-foam tests showed similar results, with foam retaining some stability even in the presence of oil for the surfactants that were analyzed in both bulk form and in porous media. Oil-wetness was found to have a detrimental effect on foam strength: Values of MRF were approximately one order of magnitude lower than those measured in the water-wet porous media. However, the decrease in MRF was not the same for all surfactants. The best-performing surfactant in the oil-wet pack was not the same as the best performer in the water-wet pack, proving the value of these additional tests. The goal of the protocol is to obtain a method for rapid testing the foaming performance and stability of a range of surfactants under conditions that are as realistic as possible. The most-promising surfactant(s) identified by use of this protocol are then selected to be evaluated further in long consolidated cores.