Insights into the high temperature-induced failure mechanism of bentonite in drilling fluid

Designing ultrahigh-temperature water-based drilling fluid for an ultra-deep well is a long-standing critical technical problem. Unraveling the failure mechanism of clay in the drilling fluid at ultrahigh temperatures harbors tremendous scientific and industrial significance. Herein, the high-temperature failure mechanism was elucidated by molecular dynamics (MD) simulation, the multi-characterizations (e.g., XPS, Zeta potential, XRD, SEM, Contact angle, and FT-IR) together with the rheology and filtration experiments. It was found that high temperature could destroy the layered structure of clay in the drilling fluid, leading to reduction of aluminum element and hydroxyl species on its surface, thus reducing the amount of negative electricity of clay and its hydrophilicity. As a result, the size of the clay particle in the drilling fluid increased, and the as-formed filter cake was thicker and looser. Furthermore, the rheology and fluid loss performance of the drilling fluid degraded or disrupted. When the temperature increased from 25 to 200 degrees C, the amount of hydroxyl group on the surface of the clay reduced by 45%. Moreover, the median size of clay particles increased by 2.7 times and the fluid loss increased by 1.6 times. The insights and methodology reported here shed new light on the fundamental understanding of failure mechanism in drilling fluid and may pave the way for improving the efficiency of drilling fluid at high temperature.