The subject of rock–fluid interaction is important in cases where flow through porous media is occurring. One special case is when the fluid reacts with the porous matrix. In this case, the mass transfer and reaction rate control the dissolution pattern. This article aimed to study the interaction between an acid nanoemulsion system and a carbonate porous media. Nanoemulsions were developed to retard the rock’s dissolution and to promote the formation of conductivity channels. Nanoemulsions were prepared using ALK100 (alkyl alcohol ethoxylate) and RNX110 (alkylphenol ethoxylate) (nonionic surfactants), sec-butanol (co-surfactant), xylene isomers (oil phase), and a solution of HCl (aqueous phase). The obtained systems were characterized in terms of surface tension, droplet diameter, and reactivity. X-ray fluorescence/diffraction (XRF/XRD) and X-ray microtomography (microCT) were performed on carbonate porous media samples treated with the acid systems in order to observe the effects of the fluid–rock interaction. The results showed that the acid nanoemulsion, presenting a low oil content formulation, showed the low surface tension and droplet size characteristic of nanoemulsions. It was experimentally verified that the reactivity in the nanoemulsion media was mass-transfer-retarded, and that the wormhole pattern was verified under the studied conditions.

Conventional treatment of drill cuttings, as drying and thermal desorption, is failing to meet environmental and economic standards; therefore, new alternatives for the treatment of this waste must be developed. The purpose of this study was to remove n-paraffin from drill cuttings using microemulsion systems (MES). The extraction percentage (%) of n-paraffin was quantified by gas chromatography with a flame ionization detector. The optimization of extraction parameters showed that the extraction percentage (%) is directly proportional to the stirring speed and contact time and inversely proportional to the HLB of the surfactant used in the microemulsion system. Results for MES using Alkonat^® L90 and Renex^® 95 were similar, but Alkonat^® L90 was chosen as the best system considering the environmental issue. The MES/cuttings ratio did not influence the percentage of n-paraffin extracted, reaching 55.03% and 56.32% for the ratios of 0.5 and 2.0, respectively. The reuse of MES in multiple extractions showed that MES can be reused in up to two extractions, obtaining up to 86% extraction. The optimal parameters for Alkonat^® L90 microemulsion systems were MES/cuttings ratio of 1.0, stirring speed of 132 strokes, and contact time of 80 min, achieving 86.27% extraction. Results obtained in this study may help to better understand n-paraffin removal from drill cuttings by MES, considering the future use of this technology in the design of an industrial treatment plant for both onshore and offshore operations.

Aromatic solvents, such xylene and toluene, are widely used in the organic damage removal operations, although increasing environmental requirements have encouraged the research for new environmental-friendly solutions to replace these solvents. Microemulsions are thermodynamically stable multicomponent systems known by their notable solubilization capability. This paper describes the preparation and investigation of a low-oil-content microemulsion system able to remove the organic damage and restore the permeability. The damage removal efficiency, for the microemulsion systems prepared, was comparable to xylene. The results showed that the proposed microemulsion formulation is a cost-effective and environment-friendly alternative to aromatic solvents.

The application of Enhanced Oil Recovery (EOR) methods is essential to promoting increase in the oil recovery where the conventional recovery methods unsuccessful. Numerous studies have demonstrated that microemulsion and surfactant systems injection can change the properties of fluids and increase the oil recovery. In this work, flooding tests were carried out combining brine and microemulsion in different proportions and schemes of injection. Microemulsion systems constituted by: Ultramine 200, n-butanol, kerosene and water were obtained and characterized by measurements of droplet diameter, surface tension, interfacial tension (IFT), and viscosity. The surfactant concentration in the microemulsion was evaluated on the oil recovery through flooding experiments. This study also evaluated how surface and interfacial tensions influence crude oil recovery (29° API). Results demonstrate that the oil recovery increases with the increase in surfactant concentration in the microemulsion. However, that increase is significant only up to 9 wt%, reaching an additional 21% oil recovery of the original oil in place (OOIP). This research recommends chemical method to EOR tests by combined injection from microemulsion and brine. The chemical action of microemulsion system results in a miscible phase, promotes oil mobilization, improve brine flooding, and increase the oil recovery. Graphical Abstract

The understanding of the mechanisms that affect oil production in carbonaceous reservoirs has become increasingly necessary, particularly in limestone, which mostly features oil wettability properties that diminishes petroleum recovery. The objective of this work was to investigate the ability of anionic surfactant (coconut oil derived soap) to adsorb in limestone in order to promote wettability change. The finite-bath technique was employed with changes in temperature, mass of adsorbent material (limestone), contact time and surfactant concentration. Contact angle and zeta potential measurements were also made. The surfactant could be significantly adsorbed on the rock, possibly due to ions that are charged oppositely to the species on the rock surface. A temperature rise from 30 °C to 50 °C was unfavourable to the adsorption capacity. The oil-wettable in-natura limestone had its wettability reduced after the treatment with surfactant. The zeta potential measurements showed that electrostatic attractions play an important role in the adsorption process.