Chelating agents’ application for well stimulation is gaining more and more interest, as they can perform under harsh conditions. However, the mutual influence of surfactants and chelating agents on the wettability alteration of hydrophobic carbonate rock under conditions of high-temperature well stimulation is relatively unexplored. This paper aims to study interfacial processes on the surface of hydrophobic rock in the presence of the EDTA-based chelating agent and surfactants of different classes. Cationic (cetyltrimethylammonium bromide, CTAB, and cetylpyridinium bromide, CPB), anionic (sodium dodecyl sulfate, SDS), and amhoteric (alkyldimethyl aminooxide, AO) surfactants were studied. Wettability alteration of model hydrophobic rock was studied under conditions specific to well stimulation. It was shown that chelating agent (CA) alone and its mixture with SDS could not lead to sufficient wettability alteration. CTAB, CPB, and AO were able to change the wettability effectively. A synergistic effect between CA and these surfactants was observed and a possible mechanism was proposed. AO was selected as the most promising surfactant. The influence of surfactant on the CA’s dissolution capacity towards carbonate rock was investigated; dissolution capacity strongly depends on wettability alteration. Finally, the effect of CA, AO, and their mixture on the wettability of aged reservoir rock was studied and the absence of negative effects was proven.

Chelating agents’ application for EOR and well stimulation is fast growing nowadays. However, reagents of this class have some drawbacks, with high values of interfacial tension (IFT) being among them. IFT may be lowered with the addition of surfactants; however, the simultaneous application of chelating agents and surfactants has not yet been widely studied. This paper focuses on the experimental and theoretical investigation of the interaction between chelating agent (ethylenediaminetetraacetic acid, EDTA) and surfactants of anionic and cationic types (sodium dodecyl sulfate, SDS, and dodecyl trimethynlammonium bromide, DTAB). IFT measurement was performed at ambient conditions, with normal octane being as the reference hydrocarbon to eliminate the temperature and salinity effects and compare surfactant-containing systems. The experimental results show that chelating agents’ addition to the solutions of surfactants leads to a decrease in IFT value. Moreover, surfactants’ critical micelle concentration is lowered, whereas their effectiveness and efficiency are increased, which points to the salting-out nature of chelating agents. Molecular dynamics reveal that chelating agent addition causes closer packing of surfactant layer, the decrease in head groups’ hydration, and, at least in the case of SDS, specific surfactant–chelating agent attractive interaction. These molecular-level insights, experimental dependencies, and the combined methodology may be useful for the proper selection of fluids for real-field operations.

Acid treatments are one of the methods for intensifying oil and gas production. Corrosion is a significant factor affecting the performance of oilfield equipment. There are many different methods of preventing corrosion, but corrosion inhibitors are most commonly used in industry. The protective effect of the inhibitor is directly determined by the effective adsorption of surfactants on the metal surface. For an indirect assessment of the adsorption of the inhibitor, a comprehensive research method is proposed based on the determination of the interfacial tension of acid compositions and steel plates’ contact angle of wetting after corrosion tests. It was found that in hydrochloric acid the adsorption of the inhibitor IC-1 reaches a maximum after 6 h, an increase in the acid concentration in the range of 5–15% wt. has a negative effect on the activity of the inhibitor. For sulfamic acid, the maximum adsorption of the IC-2 inhibitor is observed after 24 h, an increase in acid concentration has a positive effect on surfactants.

Different problems may occur during acid treatment of oil reservoirs because of the incompatibility of acid with rocks and fluids. One of the issues is the formation of acid-in-oil emulsions, which block pore throats and hinder acid removal. The standard “bottle-test” method does not fully characterize such emulsions and allows only quick reagent selection. This article presents a new methodology that enables the evaluation of emulsion formation and the possible risk for acid treatment. This methodology includes visual control and measurement of viscosity, interfacial tension, and voltage stability. We found that HCl-based emulsions are generally more viscous, finer, and stable, but the high strength of the acid may lead to emulsion breakdown. We also established that emulsions that are stable under static conditions may break down after applying mechanical stress, which is a characteristic of sulfamic acid-based emulsions. Although it may not be possible to separate emulsions visually, a water content gradient may be observed in an emulsion column. Our results demonstrate that the acid and oil parameters are interconnected in emulsion formation issues. This methodology and the obtained results may be applied for quick and proper reagent selection for better acid treatment results. Graphical Abstract

Most part of all additives to technological fluids for acid treatments of oil-extracting wells are surfactants. One of approaches to assess the behavior of surfactants in these compositions is to determine the interfacial tension of their solutions at the interface with hydrocarbons. The interfacial tension of surfactant—acid compositions based on hydrochloric and sulfamic acids and also on distilled water without addition of acids. The interfacial tension was determined at the boundary with n-octane, kerosene, and oil with different polarities and contents of natural surfactants. It was shown that n-octane and kerosene are model systems that allow conditional comparison in activity between surfactants. A dependence was found of the interfacial tension of a surfactant—acid formulations on the nature of an acid: sulfamic acid affects the activity of surfactants positively, and hydrochloric acid, negatively. The interfacial tension parameter being determined is strongly affected by the type of a surfactant. It was shown that the nonionogenic surfactant Neonol AF 9–12 shows the smallest values of the interfacial tension in the formulations based on distilled water, and the anionic surfactant Nezhegol, in acid formulations, which is due to the interaction of the functional group of a surfactant with hydroxonium ions present in solution.