Complexation of Surfactant/β‐Cyclodextrin to Inhibit Surfactant Adsorption onto Sand, Kaolin, and Shale for Applications in Enhanced Oil Recovery Processes. Part I: Static Adsorption Analysis

Abstract

Surfactant adsorption onto solid surfaces is a major issue during surfactant flooding in enhanced oil recovery applications; it decreases the effectiveness of the chemical injection making the process uneconomical. Therefore, it was hypothesized that the adsorption of surfactant onto solid surfaces could be inhibited using a surfactant delivery system based on the complexation between the hydrophobic tail of anionic surfactants and b-cyclodextrin (b-CD). Proton nuclear magnetic resonance spectroscopy was used to confirm the complexation of sodium dodecyl sulfate (SDS)/b-CD. Surface tension analysis was used to establish the stoichiometry of the complexation and the binding constant (K a ). Static adsorption testing was applied to determine the adsorption of surfactant onto different solids (sandstone, shale, and kaolinite). The release of the surfactant from the b-CD cavity was qualitatively evaluated through bottle testing. The formation of the inclusion complex SDS/b-CD with a 1:1 stoichiometry was confirmed. The K a of the complexations increases as salinity and hardness concentration increases. The encapsulation of the surfactant into the b-CD cavity decreases the adsorption of surfactant onto solid surfaces up to 79 %. Qualitative observations indicate that in the presence of solid adsorbents partially saturated with crude oil, the b-CD cavity releases surfactant molecules, which migrate towards the oil-water interface.

New Surfactant Delivery System for Controlling Surfactant Adsorption onto Solid Surfaces. Part I: Static Adsorption Tests

“…In all cases, the t statistic for related samples analysis indicated that the use of the SDS/β‐CD inclusion complex significantly inhibits the adsorption of surfactant onto the solid adsorbents with adsorption reductions ranging from 64–71 % as indicated by Figure . These observations validate previous observations …”

“…Several mechanisms have been proposed in our previous research to explain the significant adsorption inhibition of the surfactant onto solid surfaces . These mechanisms include steric hindrance due to the encapsulation of the hydrophobic surfactant tail into the β‐CD cavity that disrupts the formation of surface aggregates or hemimicelles, by interfering with the packing of surfactant molecules in the adsorbed layer and laterally between adsorbed surfactants.…”

“…These inhibition mechanisms are surface dependent, thus based on the type of porous media some of these mechanisms may prevail over others. More details on these mechanisms can be found elsewhere …”

“…The calculation of the exact amount of the final surfactant concentration , from the bulk solution at the conclusion of the static adsorption tests was indirectly obtained, because the bulk solutions also contained β‐CD (in the tests conducted using the surfactant:β−CD inclusion complex). In our previous research, it was determined through static adsorption baseline tests performed at the same experimental conditions of this work that β‐CD does not show adsorption onto sandstone surfaces. Furthermore, it was observed that small amounts of organic compounds leached from the solid adsorbents (sandstone, kaolin, and shale).…”

“…In our previous work, it was determined that the dominant molar ratio of the inclusion complex for the SDS/β‐CD was 1:1 and that the association constants values for the SDS/β‐CD inclusion complex range from 35–752 1/mol/L as a function of the salinity of the solution . The objective of this work was the evaluation of the effectiveness of the SDS/β‐CD inclusion complex in controlling the adsorption of surfactant towards solid surfaces.…”