The contradiction between the sag stability of weighted materials and the rheological properties of drilling fluids is one of the main technical difficulties in high-density drilling fluids. Thus, understanding the suspension mechanism of weighting materials is the key to improving the sag stability of weighting materials. In this study, micro-manganese (Mn3O4) was compared with the commonly used weighting agent barite to study the suspension mechanism of Mn3O4. The weighting effect of Mn3O4 and barite was evaluated by static and dynamic sag tests, rheological property measurements and filtration property tests. The evaluation experiment results showed that the sag stability of Mn3O4 was better than that of barite, and Mn3O4 could significantly increase the suspension capacity of drilling fluids and improve their rheology property. The scanning electron microscopy (SEM) and other test results indicate that the small and uniform spherical structure of micro-manganese not only causes it to have less friction, but also intense Brownian motion in drilling fluid, which weakens the sag caused by gravity. The large specific surface area of Mn3O4 results in the strong adsorption of water molecules and polymers in drilling fluids, resulting in the formation of a hydrated film on the surface of the Mn3O4 particles and physical crosslinking with polymer chains. This prevents sagging caused by the adsorption of small particles to form large particles. The key findings of this work are expected to provide a basis for improving the sag stability of weighting materials in drilling fluids and better the application of micro-manganese in drilling fluids.
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