| It is a great challenge for drilling and completion to remove oil soluble filter cake,and clean the oil based drilling fluid which is attached to the inner wall of the casing.According to existing problems of the reversible emulsion drilling fluid and the high stability of Pickering emulsions,we envisage by changing the concentration of surfactant to activate the solid particles surface in situ.The wettability change of the solid particles will induce phase transition of the oil based drilling fluid.With the addition of high concentration of surfactant,the surfactant YLZ-3 will adsorb on the surface of nano calcium carbonate solid particles.When the concentration of surfactant is greater than 1mM,the emulsion type will change from water in oil to oil in water,and the emulsion type will change from oil in water to water in oil after continuing to add the surfactant YLZ-3 up to a concentration of 100 mM.After the adsorption of the surfactant YLZ-3 on nano calcium carbonate particles,the Zeta potential of particles will decrease from 7mV to OmV and then gradually increased to-41 mV,the contact angle will increase from 38.97° to 125.46° and then decreased to 52.31°,which reveals the surfactant YLZ-3 can change the wettability of nano calcium carbonate solid particles from hydrophilicity to hydrophobicity and then to hydrophilicity,and induce a emulsion double phases inversion.The single-layers and double-layers adsorption of YLZ-3 on the surface of the solid particles is verified by MD simulation on the molecular level.Changing concentrations of the surfactant TNX may induce the phase of bentonites particles stabilized emulsions changing from oil in water to the oil in water when the concentration of surfactant is greater than 7.5mM,and then convert to oil in water when the concentration of surfactant is greater than 25mM.Increasing surfactant concentration,surfactant TNX will be adsorbed on bentonite.The zeta potential of the bentonite will decrease from-39mV to 0 mV and then increased to 54mV,and the contact angle of the bentonite will increase from 21.24° to 137.21° and then reduce to 24.37°,which reveals the wettability of bentonite particles undergoes a transition from strong hydrophilicity to hydrophobicity and then to the hydrophilicity,it will induce a emulsion double phases inversion.The inorganic salt concentration,pH and emulsion preparation temperature have little effect on the double phase inversion.The surfactant can induce a reversible phase transition of the solid particles stabilized oil based drilling fluid.By testing the rheological property and the API filtrate value of the system,we can find that each type of emulsion has better shear thinning property and lower API filter loss. |
