Insights into the carbonate/bicarbonate ion-induced failure mechanism of bentonite in drilling fluids

Abstract

During deep oil and gas drilling, drilling fluids are often polluted with carbon dioxide (CO2). The intrusion of CO2 can affect bentonite performance, leading to deterioration or even failure of drilling fluids. To further investigate the influence of CO2 pollution on the bentonite and its failure mechanism, Na2CO3 simulation experiments were conducted. Performance evaluation showed that as the concentration of HCO3− and CO32− increased, the viscosity, filtration loss, and mud cake permeability of drilling fluids significantly increased. Meanwhile, the drilling fluid foaming was particularly evident. Mechanism studies indicated that the adsorption of HCO3− and CO32− on the bentonite diminished the electrostatic interactions and interlayer spacing between particles, leading to the particles aggregation and a decrease in Zeta potential, ultimately causing the hydration film on the bentonite to become thinner. Simultaneously, this also led to a decline in the dispersibility of bentonite. This study can offer a new research thread for the failure mechanism of bentonite under CO2 pollution and indicate the direction for the study of drilling fluid resistance to acidic gas pollution.