Abstract
Surfactant losses by adsorption to rock surfaces make surfactant-based enhanced oil recovery economically less feasible. We investigated polyacrylate (PA) as a sacrificial agent in the reduction of anionic surfactant adsorption with focus on calcite surfaces by using quartz crystal microbalance with dissipation monitoring. It was found that the adsorption of the anionic surfactant alcohol alkoxy sulfate (AAS) followed a Langmuir adsorption isotherm, and the adsorbed amount reached saturation above its critical micellar concentration. Adsorption of PA was a much slower process compared to AAS adsorption. Increasing the calcium ion concentration also increased the amount of AAS adsorbed as well as the mass increase rate of PA adsorption. Experimental results combined with density functional theory calculations indicated that calcium cation bridging was important for anionic surfactant AAS and PA adsorption to calcite surfaces. To effectively reduce the amount of surfactant adsorption, it was needed to preflush with PA, rather than by a simultaneous injection. Preflushing with 30 ppm of PA gave a reduction of AAS adsorption of 30% under high salinity (HS, 31,800 ppm) conditions, compared to 8% reduction under low salinity (LS, 3180 ppm) conditions. In the absence of PA, the amount of adsorbed AAS was reduced by already 50% upon changing from HS to LS conditions. Lower calcium ion concentrations, as under LS conditions, contributed to this observation. On different mineral surfaces, PA reduced the AAS adsorption in the order of alumina > calcite > silica. These results offer important insights into mitigating surfactant adsorption using PA polyelectrolyte as sacrificial agent and contribute to improved flooding strategies with reduced surfactant loss.
Highlights
With the growing demand for oil production and achieving more efficient extraction of residual oil from petroleum reservoirs, tertiary oil recovery, known as enhanced oil recovery (EOR), has been receiving substantial attention [1,2]
We first investigated the separate adsorption of alcohol alkoxy sulfate (AAS) and PA on calcite sensors by using quartz crystal microbalance with dissipation monitoring (QCM-D) at room temperature (23 ± 0.1 °C) in aqueous 50 mM CaCl2 at pH = 9.5
We have found that PA polyelectrolytes are able to act as sacrificial agent to reduce the adsorption of the anionic surfactant AAS to the mineral surfaces as deduced from QCM-D measurements, which were performed for the first time
Summary
With the growing demand for oil production and achieving more efficient extraction of residual oil from petroleum reservoirs, tertiary oil recovery, known as enhanced oil recovery (EOR), has been receiving substantial attention [1,2]. Added alkali like sodium carbonate has been used to increase the local pH, and increasing the negative charge density of the surface, which leads to a reduction of anionic surfactant adsorption [20] Another important factor influencing the surfactant adsorption to rock surfaces is the ionic compositions of the surfactant flooding solution [21,22,23]. Divalent cation, such as Ca2+, is capable of acting as ionic bridges between anionic surfactants and negatively charged surfaces, and favoring anionic surfactant adsorption [23,24,25]. To alleviate the drift effects of signals, each sensor was utilized less than five times
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