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Graphical abstract Abstract This work aims to investigate the changes in the shear and oscillation responses of an ethoxylated alkylamine emulsion with the addition of acetic acid and establishes their relationships with the emulsion phase inversion. The initial emulsion behaves as a non-Newtonian fluid exhibiting shear thinning with a viscoelastic gel structure (at rest). Upon the addition of acetic acid, the emulsion first transforms to a structureless (at rest) non-Newtonian fluid with lower viscosity and worse shear thinning compared with the initial state and then converts back to a non-Newtonian fluid with a higher gel strength, higher elasticity (at rest) and better shear thinning than the initial state as the phase inversion proceeds from an oil-continuous stage to a bicontinuous stage. This regained non-Newtonian character can be maintained throughout the whole bicontinuous stage and can even extend to the beginning of the water-continuous stage which is obtained from the bicontinuous stage by increasing the acetic acid content; however, it is ultimately replaced by a structureless (at rest) non-Newtonian fluid that exhibits lower viscosity and worse shear thinning compared with the initial state as the acetic acid content increases. The establishment of relationships among the interfacial moduli and deformation, geometrical factors (i.e., interfacial curvature, droplet shape and size and positional structure) and the liquid crystal phase behaviors help to elucidate the mechanisms that control the rheological transitions of emulsions. Based on these results, a novel water-washable viscoelastic emulsion drilling fluid is proposed. [ABSTRACT FROM AUTHOR]

Clay is closely associated with the drilling of oil and gas by influencing the shale wellbore stability and the rheology of drilling fluids. In this work, four imidazolium-based ionic liquids (ILs) were used to modify the typical clay (i.e., sodium bentonite (Na-Bent)), and their effects on the Na-Bent rheological and swelling properties were evaluated by shear rheological measurements, immersion experiment, linear swelling measurements. The mechanisms involved were identified by using fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Zeta-potential and environmental scanning electron microscopy (ESEM) analysis. Evaluation experiment results showed that the adsorption of each IL could both significantly affect the Na-Bent rheological property and inhibit the Na-Bent swelling, which strongly depended on ILs' structures and concentrations. The mechanism study revealed that the cationic groups of ILs could adsorb on Na-Bent prior to water molecules, followed by expelling water and compressing the double electrode layers, and therefore inhibit the Na-Bent swelling. The adsorption of ILs could also change aggregation behaviors of the Na-Bent particles, by which the "house of cards" structures in Na-Bent dispersions were improved or destroyed, resulting in changes in rheological properties of Na-Bent dispersions. Unlabelled Image • An ionic liquid (IL) can affect the clay rheological and swelling behaviors • Effects of IL on clay depend on IL's structure and concentration • Preferential adsorption of IL expels water and compresses double electrode layers • IL inhibits clay swelling by minimizing crystalline and osmotic hydration of clay • Changes of "house of card" structure account for the clay rheological transitions [ABSTRACT FROM AUTHOR]