Doctor of Philosophy (PhD)


Petroleum Engineering

Document Type



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. 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. Due to the large number of experiments in this study, standard wettability measurement methods were not used due to the time and expense it takes to run a single experiment. To overcome this barrier, the modified flotation technique (MFT) was developed. This wettability measurement method is fast reliable, and can serve both as a screening tool and provide quantitative results. 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.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Radonjc, Mileva