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Reversible invert emulsion muds (RIEMs) offer unique advantages over other oil-based muds for the completion of a well due to the pH-responsiveness of reversible emulsifiers. This paper presents new insights into the effects of pH-responsiveness on the completion performance of RIEMs and the mechanisms involved. At pH 4 and 6, RIEMs are easy to remove, but the formation damage is relatively severe. At pH 10, the removal of RIEMs is relatively difficult but can be facilitated by intense and repeated flushes. Once the mud has been removed, there is little formation damage. At pH 8, the mud is very difficult to remove, and the greatest amount of formation damage is observed. The spontaneous curvature of the surfactant layer changes at pH 4 and 6, resulting in the emulsion inversion and thereby enabling the removal of RIEMs by the solvent effect. These changes do not occur at pH 8 and 10. More emulsifiers adsorb to the rock surface at pH 4, 6, and 8, resulting in a strongly oil-wet condition and high formation damage. The desorption of emulsifiers occurs at pH 10, causing a water-wet condition and low formation damage. The variety in chemical states accounts for the changes in the adsorption behavior of the emulsifiers. [ABSTRACT FROM AUTHOR]

In this paper, the inhibition of chitosan quaternary ammonium salt (HTCC) in the drilling fluid was studied. The inhibition was evaluated by linear swelling test, mud making test and rolling recovery. The results indicated that the inhibition of HTCC was better than polyether amino, which be used widely in the oil flied as the excellent shale inhibitor. Especially HTCC is an environmental friendly and biodegradable. The inhibition mechanism of HTCC was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, Scanning electron microscopy, Zeta potential, Gel strength measurement analysis. The negative charge in the surface of montmorillonite (MMT) was neutralized by the positive charge. HTCC was absorbed and coated in the surface and intercalated in the interlayer of MMT, which reduced the hydration repulsion of diffuse electric double layer and leaded to the inhibiting hydration of clay. Hydrogen bonding between hydroxyl, amino groups in the HTCC and the surface of clay can be formed in the process. The coordination of electrostatic interaction and hydrogen bonding prevented the water molecules from the gallery of clay, which resulted from the absorption and intercalation of HTCC in the surface and interlayer of MMT. The high molecular weight of HTCC was coated in the surface of MMT, which further expelled the hydration swelling of clay. It kept the high inhibition even if the ether bond hydrolysis partly in high temperature, comparing to polyether amino which the inhibition be reduced. [ABSTRACT FROM AUTHOR]

In this paper, the nano terpolymer of acrylamide (AM), 2-acrylamido-2-methyl -1-propane sulfonic acid (AMPS), N-vinyl-pyrrolidone (NVP) was synthesized by free radical polymerization in water solution. The addition of ethanol was used to control molecular weight of terpolymer. The plugging properties and mechanism of terpolymer were studied. The characterization and properties of nano terpolymer were studied by Fourier transform infrared spectroscopy, particle size analyzer, transmission electron microscopy. The results indicated that the structure of terpolymer was consistent with design. It was nano material in water and kept on nanoscale stable in drilling fluid. The filtration property of terpolymer was studied by drilling fluid filter press and the results indicated that the filtration property of terpolymer was equal to fluid loss agent. Nevertheless, the addition of inorganic nanoparticles resulted in high amount of filtration volume in the same conditions because of extensive agglomeration of inorganic nanoparticles. The stability of nano materials in solution was requirement to plug nanopores. The resistance properties to salinity, calcium and high temperature were studied, and the results showed that the properties were better than PAC which is widely used in oil flied as fluid loss agent. The plugging properties of terpolymer were studied by specific surface and porosity physical adsorption instrument (BET) and the membrane efficiency tester. BET results showed that the surface area of natural rock reduced after treated with terpolymer, indicating terpolymer entered into nanopores of shale because of the adsorption in the surface of shale. In study of the membrane efficiency test, the addition of terpolymer resulted in significantly reducing of shale permeability. It was further presented that nanopores of shale were plugged by terpolymer. [ABSTRACT FROM AUTHOR]