Nano laponite as a potential shale inhibitor in water based drilling fluid for stabilizing wellbore stability and mechanism study

Shale hydration is a main reason to cause wellbore instability in oil and gas drilling operations. In this study, nano laponite as the shale inhibitor was employed to stabilize the wellbores. The inhibition property of laponite suspensions was evaluated by immersing experiment, linear swelling measurement and shale recovery test. Then the shale inhibition mechanism was studied by using capillary suction time (CST) measurement, 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 KCl and polyester amine. 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 laponite nanofluid could allow to form a nano film to reduce water invasion into formation; and the nanoscale laponite particles could substantially reduce shale permeability and form less porous surfaces. Furthermore, laponite could considerably decrease filtrate volume of drilling fluid while KCl and polyester amine had negative influences on the properties of drilling fluid. This approach described herein might provide an avenue to inhibit shale hydration.