Evaluation of Cyclodextrins as Environmentally Friendly Wettability Modifiers for Enhanced Oil Recovery

In the present work, the use of Cyclodextrins (CDs) as wettability modifiers for enhanced oil recovery (EOR) was evaluated. Cyclodextrins (CDs) are cyclic oligosaccharides that form inclusion complexes with various organic molecules, including n-alkanes. Wettability was evaluated through the contact angle (theta) of an n-dodecane drop in contact with a quartz surface and immersed in a 0.6 M NaCl aqueous solution containing the CDs. The quartz surface was functionalized with octadecyltrichlorosilane (OTS), rendering the surface oil-wet (C-18-quartz). Here, the n-dodecane, the saline solution and the C-18-quartz represent the oil, the reservoir brine and an oil-wet rock surface, respectively. In the absence of CDs, the n-dodecane drops spread well over the C-18-quartz, showing that the surface was oleophilic. In the presence of CDs, remarkable effects on the wettability were observed. The most dramatic effects were observed with alpha-cyclodextrin (alpha-CD), in which case the C-18-quartz surface changed from oil-wet (theta = 162 degrees) in the absence of CD to water-wet (theta = 33 degrees) in the presence of 1.5% (w/v) alpha-CD. The effects of the CDs can be explained by the formation of surface-active inclusion complexes between the CDs and n-dodecane molecules. The CD inclusion complexes can be regarded as pseudo-surfactants, which are less harmful to the environment than the traditional surfactants employed by the petroleum industry.