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http://hdl.handle.net/10136/145
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| Title: | Adsorption and desorption studies of some model surfactants from oil-based drilling fluids |
| Authors: | Bryant, Elizabeth Michelle |
| Keywords: | Drilling muds -- Wettability |
| Issue Date: | 20-Nov-2008 |
| Abstract: | Characterization of reservoir wettability is an important part of assessment of
potential oil recovery. Oil-based drilling fluids include surfactants, which can alter the
wettability of mineral surfaces. Cores exposed to these fluids may not reflect the true
wettability of the reservoir materials.
The focus of this study was to observe wettability changes induced by adsorption
and removal of surfactants of known structure on mica surfaces using tools that are
applicable to studies of wetting alteration by crude oil components. The surfactants used
were polyethoxylated coconut and tallow amines with chain lengths of 12 and 18 carbons
and head groups consisting of two to five ethoxy groups. Mica was exposed to decane
solutions of the surfactants. The treated mica was characterized macroscopically using
contact angle measurements and microscopically using atomic force microscopy (AFM).
Upon exposure to the surfactant solutions, the mica became oil-wet (~170° for
both water-advancing and receding conditions). AFM examination of similarly treated
surfaces imaged in air revealed surfactant layers that were easily disrupted or surfaces
that showed no surfactant at all. Contact angles were in the intermediate to water-wet
range if the mica samples were removed from the surfactant solution, rinsed with nonaqueous
solvents, and submerged in decane for measurements of water/decane contact
angles. These results suggest only weak surfactant adsorption occurred from nonaqueous
solutions. Sorption was less for increased levels of ethoxylation, which was
concluded from the difference in the contact angles of TAM-2 and TAM-5; differences
due to hydrocarbon chain length were negligible, which was evident when comparing
CAM-2 and TAM-2 contact angle results. Stronger adsorption, higher contact angles,
and more stable surfactant layers could be demonstrated when mica was exposed to
aqueous solutions after surfactant sorption, depending on the pH of the aqueous phase.
Low-pH conditions that promote protonation of the surfactants’ amine headgroup
produced the greatest wetting alteration. Above a pH of 8 or 9, no surfactant remained
adsorbed on mica surfaces. |
| URI: | http://hdl.handle.net/10136/145 |
| Appears in Collections: | Theses
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| Bryant, Elizabeth M..pdf | | 2283Kb | Adobe PDF | View/Open |
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