Shale hydration is the main reason causing wellbore instability in oil and gas drilling operations. In this study, nanoscale laponite as a shale inhibitor was employed to stabilize wellbores. The inhibition property of laponite suspensions was evaluated by an immersion experiment, linear swelling measurement, and a shale recovery test. Then the shale inhibition mechanism was studied by using capillary suction time (CST) measurement, a thixotropy study, plugging performance evaluation, and related theoretical analysis. Evaluation experiment results showed that laponite had a better inhibition property than widely used inhibitors of potassium chloride (KCl) and poly(ester amine) (PA). The mechanism study revealed that integration of several factors strengthened the inhibition property of laponite suspensions. Laponite nanoparticles could plug interlayer spaces of clays by electrostatic interaction to reduce water invasion; the "house of cards" structure of laponite suspensions enables large CST values and low free water contents; the excellent thixotropy of a laponite nanofluid could allow a nanofilm to form in order to reduce water invasion into the formation; the nanoscale laponite particles could substantially reduce the shale permeability and form less porous surfaces. Furthermore, laponite could considerably decrease the filtrate volume of the drilling fluid, while KCl and PA had negative influences on the properties of the drilling fluid. This approach described herein might provide an avenue to inhibit shale hydration.

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Wellbore instability caused by water invasion is the main problem in oil and gas drilling operation. This study reports the utilization of a hydrophobic-associated polymer-based laponite nanolayered silicate composite as a filtrate reducer in water-based drilling fluids (WDFs). The thermal performance and micromorphology of the composite were analyzed by thermogravimetric analysis, transmission electron microscope, and field emission scanning electron microscopy. The results indicated that the composite possessed a "bean pod" structure and a good thermal stability. The rheological properties of the composite solution were evaluated. The results showed that the hydrophobic association interaction of the composite is weak but existent, and the crosslink network structure is variable. The applied performances of WDFs containing the composite were also evaluated. Evaluation results showed that the composite could improve the properties of the thermal stability, salt tolerance, and fluid loss control of WDFs. The particle size distribution of WDFs and the micrographs of filter cakes explained the improving. The composite was expected to be applied as an efficient filtrate reducer for developing high performance drilling fluids.

This study presents an alternative method to enhance the emulsion stability of oil based drilling fluids (OBMs). Modified dimer acid (MDA) was synthesized with a molecular structure having two hydrophilic heads and two hydrophobic tails. Theoretically, the adsorption of MDA on an oil-water interface makes it possible to increase hydrogen bonding between water droplets and form three dimensional networks which benefit emulsion stability. The influence of MDA on the stability of base emulsions was studied by visual observation. Then the stabilization mechanism of MDA was analyzed from the micro and macro points of view by morphology study using a cryo-scanning electron microscope (cryo-SEM) and rheological measurements including viscosity vs. shear rates, zero-shear viscosity (h 0 ), and creep and recovery tests. Experimental results showed that a substantial improvement in emulsion stability was visually observed when the MDA concentration was 2 g L À1. From cryo-SEM observation, a honeycomb structure was observed in the emulsion containing 2 g L À1 MDA, which can provide a physical barrier to restrain the movement of water droplets. In comparison with the rheological behaviors of the emulsion without MDA, a remarkably larger zero-shear viscosity, a solid-like behavior and a greater elasticity were observed when 2 g L À1 MDA was present. Finally, the application in OBMs shows that MDA can largely enhance electrical stability (ES) and reduce the filtration volume. The method proposed in the paper could be used to enhance the stability of w/o emulsions in a variety of fields.