Role of Wettability on the Adsorption of an Anionic Surfactant on Sandstone Cores

Abstract

We investigate the dynamic adsorption of anionic surfactant C 14 − 16 alpha olefin sulfonate on Berea sandstone cores with different surface wettability and redox states under high temperature that represents reservoir conditions. Surfactant adsorption levels are determined by analyzing the effluent history data with a dynamic adsorption model assuming Langmuir isotherm. A variety of analyses, including surface chemistry, ionic composition, and chromatography, is performed. It is found that the surfactant breakthrough in the neutral-wet core is delayed more compared to that in the water-wet core because the deposited crude oil components on the rock surface increase the surfactant adsorption via hydrophobic interactions. As the surfactant adsorption is satisfied, the crude oil components are solubilized by surfactant micelles and some of the adsorbed surfactants are released from the rock surface. The released surfactant dissolves in the flowing surfactant solution, thereby resulting in an overshoot of the produced surfactant concentration with respect to the injection value. Furthermore, under water-wet conditions, changing the surface redox potential from an oxidized to a reduced state decreases the surfactant adsorption level by 40%. We find that the decrease in surfactant adsorption is caused not only by removing the iron oxide but also by changing the calcium concentration after the core restoration process (calcite dissolution and ion exchange as a result of using EDTA). Findings from this study suggest that laboratory surfactant adsorption tests need to be conducted by considering the wettability and redox state of the rock surface while recognizing how core restoration methods could significantly alter the ionic composition during surfactant flooding.

Distinguishing the Effect of Rock Wettability from Residual Oil on Foam Generation and Propagation in Porous Media

“…It should however be noted that the 100% gas injection test was conducted after 2 PV of the surfactant solution was injected, which could potentially alter the rock wettability toward a more water-wet condition. 62 To verify this hypothesis, a surfactant-flooding was implemented on a separate core (B*), prepared under similar conditions as core B. Figure 4a and 4b show the collected effluent samples and the produced surfactant concentration, measured with the potentiometric titration method.…”

“…62 Under similar experimental conditions, surfactant adsorption on Berea sandstone was satisfied after 1.5 (water-wet) to 2.0 PV (neutral-wet) of surfactant solution was injected. 62 Here, the injected surfactant solution, prior to the foam-flood, was 2 PV in the tests A and B (Berea cores) and 10 PV in the tests C−F (reservoir cores). Even though adsorption tests were not directly measured with reservoir cores, the adsorption was assumed to be satisfied within 10 PV of injection.…”

A Mathematical Model of Surfactant Spontaneous Imbibition in a Tight Oil Matrix with Diffusion and Adsorption

“…Although the technologies of horizontal wells and hydraulic fracturing have been successfully applied to develop unconventional oil resources, the resulting oil recovery factor is commonly less than 10%. , As an important mechanism of improving oil recovery in unconventional oil reservoirs, spontaneous imbibition (SI) has been widely studied. , The oil recovery of SI is affected by many factors, such as rock wettability, pore structure, and fluid properties. − In water-wet unconventional oil reservoirs, water can be spontaneously imbibed into the matrix, resulting in oil production driven by capillary forces. − However, the SI process is very slow in unconventional oil reservoirs because of the tiny pore throat sizes, and for oil-wet unconventional oil reservoirs, SI cannot occur . Surfactants can accelerate the SI process and change the rock wettability from oil-wet to intermediate-wet or water-wet, while only a small amount of surfactant is required. − Therefore, SI with a surfactant is a promising way to improve unconventional oil recovery, and studying the mechanism of the SI of surfactant solution into oil-saturated nanopores in a tight matrix is of great significance for unconventional oil reservoir development.…”

Temperature-Responsive Hydrogel Carrier for Reducing Adsorption Loss of Petroleum Sulfonates

“…For these reasons, alkali-free chemical flooding has attracted considerable attention . There are two primary challenges involved in excluding the alkali component from ASP flooding: maintenance of the ability of the surfactant to reduce the water–oil IFT and prevention of excessive surfactant adsorption to the formation. − In our earlier work, we observed a strong dependence of the IFT of petroleum sulfonate (PS; the most commonly used surfactant for chemical flooding) on the presence of electrolytes. We also noted that NaCl could replace Na 2 CO 3 for reducing the IFT .…”