Biosurfactants and their significance in altering reservoir wettability for enhanced oil recovery

The aim of this research was to investigate the effects on reservoir rock wettability by treating oil-wet calcite and mica powder, which simulated carbonate and sandstone reservoirs, respectively, with rhamnolipid biosurfactant solutions prepared in both distilled and artificial sea water (ASW). In parallel to this primary investigation, tests were also carried out to determine the ability of rhamnolipid biosurfactants to reduce the interfacial tension (IFT) between two immiscible fluids, in this case, crude oil and water. Each sample of calcite and mica powder was modified with a 0.01 M solution of stearic acid and n-decane to ensure it was fully oil-wet, like reservoir rock. The oil-wet powder was then subjected to various treatments, which included biosurfactant treatment. To test wettability, contact angle measurements were conducted and IFT was measured using the Krüss Digital Tensiometer Model K9 equipped with a platinum ring. It was found that oil-wet mica powder became fully water-wet when it was treated with distilled water and distilled water+biosurfactant; however, the real effect was found when treating mica with any ASW solutions. The oil-wet calcite powder showed to have favorable reductions in the contact angle when treated with both distilled water+biosurfactant and ASW+biosurfactant solutions. Treatment in only distilled water and ASW did not produce reductions in the contact angle. The investigation into IFT reduction showed that the IFT between crude oil/water reduced from 18.9 to 0.1 mN/m when the rhamnolipid biosurfactant was added, which is favorable. These tests showed that treating oil-wet simulated reservoir rock with biosurfactant produces favorable reductions in wettability. This provides a good starting point for further in-depth investigations into the modification of reservoir rock wettability using biosurfactants.