EFFECT OF ADDED SURFACTANT ON INTERFACIAL-TENSION AND SPONTANEOUS EMULSIFICATION IN ALKALI ACIDIC OIL SYSTEMS/

An experimental investigation of the buffered surfactant-enhanced alka line flooding system chemistry was undertaken to determine the influen ce of various species present on interfacial tension as a function of pH and ionic strength. Phase behavior tests that monitor the extent of emulsification are sufficient to determine the region of low interfac ial tension. Optimization of interfacial tension by adjustment of the ionic strength alone may not necessarily provide the lowest interfacia l tension under the best conditions. The pH should be simultaneously o ptimized along with ionic strength to allow better control over attain ment of low interfacial tension. The dominant mechanism by which added surfactant aids in the reduction of interfacial tension is the format ion of mixed micelles with the ionized acid. Although added surfactant partitioning from the influence of the un-ionized acid and ionic stre ngth will affect interfacial behavior, the formation of mixed micelles plays a dominant role. Middle-phase formation is possible with a low acid oil using a petroleum sulfonate at a proper pH and ionic strength .