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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.

As an important industrial material, bentonite has been widely applied in water-based drilling fluids to create mud cakes to protect boreholes. However, the common mud cake is porous, and it is difficult to reduce the filtration of a drilling fluid at high temperature. Therefore, this paper endowed bentonite with a thermo response via the insertion of N-isopropylacrylamide (NIPAM) monomers. The interaction between NIPAM monomers and bentonite was investigated via Fourier infrared spectroscopy (FTIR), isothermal adsorption, and X-ray diffraction (XRD) at various temperatures. The results demonstrate that chemical adsorption is involved in the adsorption process of NIPAM monomers on bentonite, and the adsorption of NIPAM monomers accords with the D&ndash, R model. With increasing temperature, more adsorption water was squeezed out of the composite when the temperature of the composite exceeded 70 &deg, C. Based on the composite of NIPAM and bentonite, a mud cake was prepared using low-viscosity polyanionic cellulose (Lv-PAC) and initiator potassium peroxydisulfate (KPS). The change in the plugging of the mud cake was investigated via environmental scanning electron microscopy (ESEM), contact angle testing, filtration experiments, and linear expansion of the shale at various temperatures. In the plugging of the mud cake, a self-recovery behavior was observed with increasing temperature, and resistance was observed at 110 &deg, C. The rheology of the drilling fluid was stable in the alterative temperature zone (70&ndash, 110 &deg, C). Based on the high resistance of the basic drilling fluid, a high-density drilling fluid (&rho, = 2.0 g/cm3) was prepared with weighting materials with the objective of drilling high-temperature formations. By using a high-density drilling fluid, the hydration expansion of shale was reduced by half at 110 &deg, C in comparison with common bentonite drilling fluid. In addition, the rheology of the high-density drilling fluid tended to be stable, and a self-recovery behavior was observed.