This study examines the role of crude oil’s surface active compounds (SAC) in determining the reservoir wettability. Wettability describes the relative preference of a reservoir rock for oil or water. Wettability influences the distribution of fluids in a reservoir and the efficiency of oil recovery methods. Unfortunately, the chemical mechanisms controlling wettability in individual reservoirs remain hazy. The wettability measurement method used was the modified flotation technique (MFT).<br/>Wettability is conditional and is influenced by rock mineralogy, fluid chemistry, and temperature. An extensive experimental study was executed to understand the impact of naturally-occurring SACs typically found in crude oil, on the wettability of sandstone and carbonate rocks over a range of salinities and temperatures. To isolate the effects of individual SACs, this project used model oil mixtures of pure decane and SACs to represent the oleic phase. The four groups of SAC studied are:  aromatic, oxygen-bearing, sulfur-bearing, and nitrogen-bearing SACs.<br/>In the quest to determine why low salinity waterflooding is successful in increasing oil recovery in some reservoirs and not in others, this study found that it is crucial to accurately characterize crude oil, brine, and reservoir rock material. This allows one to effectively engineer injection water chemistry which would favorably alter wettability, and maximize oil recovery. The overall effect toward either oil-wet or water-wet conditions was observed to depend more on brine salinity than temperature. As salinity was decreased nitrogen SACs, non-acidic sulfur SACs, and the short chained oxygen SAC shifted the wettability of the carbonate rocks towards water-wet conditions. Long chained acids SACs, acidic sulfur SACs, and aromatics shifted the wettability of carbonates towards oil-wet conditions as brine salinity was decreased. This difference in SACs’ reaction to salinity was proposed as one of the reasons why low salinity waterflooding is successful in some reservoirs and not in others.

Impact of surface active compounds in crude oil on reservoir sandstone and carbonate rock wettability

254th National Meeting (2017)

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