Experimental investigation of the controversial effects of a cationic surfactant with brine on spontaneous imbibition of an asphaltenic crude oil

Carbonate formations, which are often naturally fractured and oil-wet, include a significant portion of the discovered oil reserves. Due to their tendency to retain oil at the rock surface, enhanced oil recovery (EOR) from these reservoirs is difficult. It has been suggested that low salinity (LS) water injection be used to recover more oil from these types of oil reservoirs. A surfactant is one of the chemicals that is broadly applied as an agent to alter wettability towards water-wet conditions. In these reservoirs, if the wettability of the reservoir rock is altered from mostly oil-wet to mostly water-wet, recovery efficiency can be greatly enhanced. In this study, the synergistic effect of a modified brine solution (i.e., increasing the concentration of (SO42-)) and a cationic surfactant, namely cetyltrimethylammonium bromide (CTAB) with two different concentrations (100 ppm and 300 ppm) on the wettability of dolomite rock was considered. The contact angle is used to assess wettability alteration from dolomite rock surface. Also, oil recovery was tested in dolomite core samples via spontaneous imbibition procedures at 60 degrees C for 30 days. Using the modified brine, the contact angle was reduced from 130 degrees to 27 degrees, and the oil recovery increased from 0% to 33%. While CTAB-surfactant decreased the contact angle from 140 degrees to 32 degrees and 120 degrees to 34 degrees, respectively, for concentrations of 300 ppm and 100 ppm. Moreover, oil recovery was increased to 7.95% and 6.60 % and at concentrations of 300 ppm and 100 ppm, respectively. The oil-wet dolomite rock wettability can be modified by using the sulfonate ion and a cationic surfactant. Indeed, by absorbing SO42- ions on the dolomite slice surface, a repulsive force is formed between SO42- and the carboxylate on its surface and the wettability changes from an oil-wet to a water-wet condition. Furthermore, electrostatic interactions between the surfactant's positively charged head and the negatively charged carboxylate cause the cationic surfactant to adsorb on the oil-wet surface. Indeed, the wettability changes to the water-wet condition when the carboxylate group is removed from the rock surface by forming an ion pair. On the other hand, for low oil recovery in surfactant imbibition, three different scenarios were considered, namely: I) reduction of cationic surfactant concentration in the Amott cell, II) oil snap-off phenomenon, and III) asphaltene deposition and plugging of the pores. The results of the three proposed scenarios are as follows: I) when re-imbibing cationic surfactant into the dolomite core surface, shifting the wettability state from oil-wet to water-wet resulted in higher oil recovery (scenario result (I)), II) after CTAB flooding into the micromodel with varied pore throats, oil could be released from the porous medium throats and the walls of pores. As a result, an increase in oil recovery was seen (scenario result (II)), and III) an oil-in-water emulsion was formed as a result of the interactions between asphaltene and the cationic surfactant, and asphaltene became more unstable. As a result, asphaltene is deposited on the rock surface, plugging pores and reducing permeability, resulting in a decrease in oil recovery (scenario result (III)). The findings of this study can help for better understanding of the impact of modified bine water and cationic surfactant on dolomite rock and the interaction between asphaltene and cationic surfactant and their impact on ultimate oil recovery. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the synergistic effect of a modified brine solution and a cationic surfactant on the wettability of carbonate rock formations. The results demonstrate that these chemicals can alter the wettability from oil-wet to water-wet, leading to a significant increase in oil recovery. Additionally, different scenarios for low oil recovery during surfactant imbibition are considered, including variations in surfactant concentration, oil snap-off phenomenon, and asphaltene deposition and pore plugging.