Using Manganese Tetroxide for Hematite Settling Prevention in Water-Based Mud

The precipitation (sagging) of solids from weighting materials, such as hematite is a challenge in high-pressure high-temperature (HP/HT) applications of drilling fluids. The result is inconsistent properties of the mud and poor fluid stability. This study provides a solution to hematite sagging in water-based mud for HP/HT wells which involves the combination of manganese tetroxide with hematite. A Field formulation of the mud was employed over a range of manganese tetroxide/hematite ratios (0/100, 10/90, 15/85, and 20/80%) in laboratory experiments to address the sag performance. From the sagging tests, the optimal combination ratio was determined. Then, density, alkalinity, rheology, viscoelasticity, and filtration behavior for the formulated mud were addressed. The tests were conditioned to 300 psi and 250 °F. The acquired results of static and dynamic sag tests indicated that incorporation of 20% manganese tetroxide solved the hematite sagging issue and bring the sag tendency within the recommended safe range. Upon the inclusion of manganese tetroxide, the density reduced insignificantly from 15.2 ppg with base hematite to 15.1 ppg for the 20% manganese tetroxide mixture and similarly the pH reduced from 10.5 to 9.9. The recommended 20/80% combination enhanced the yield point (YP) by 28% with 16% increment in plastic viscosity (PV) and resulted in a 10% improvement of the YP/PV ratio which usually is indicating better hole cleaning. Also, the gel strength was improved resulting in better solids suspension capacity. The filtration behavior of the formulation with 20% manganese tetroxide was superior compared to pure hematite since it resulted in 50% reduction of the filtrate volume and 43% improvement in filter-cake weight and thickness. This study contributes to develop a technically feasible and stabilized drilling mud using combined weighting agents for HP/HT applications, which economize the drilling cost and time by reducing the associated operational problems.