Prevention of hematite settling using synthetic layered silicate while drilling high-pressure wells

Hematite (Fe₂O₃) is used as a weighting material to increase the density of the drilling fluid. Hematite has a higher density (5.05 g/cm³) compared with barite (4.2 g/cm³). Because of the high specific gravity and particle size, hematite can separate and settle down at higher temperatures (> 250 °F). The objective of this paper is to assess the usage of laponite which is synthetic layered silicate to solve the settling of hematite particles in water-based mud (WBM). Laponite was added to the WBM in different concentrations 0, 0.25, 0.5, 0.75, and 1 lb./bbl. Static and dynamic sag tests were performed to determine the optimum quantity of laponite. The viscoelastic and rheology properties were evaluated to compare between WBM-blank and WBM-laponite. The filtration test was performed at 250 °F and 300-psi pressure difference to assess the effect of adding laponite on the filter cake thickness and filtration volume. The results showed that adding 1 lb./bbl of laponite was enough to eliminate the sag issue in both vertical and 45° inclination. The sag factor was reduced from 0.594 to 0.502 at the vertical condition and from 0.62 to 0.51 for the 45° inclined condition. For the dynamic sag, the viscometer sag shoe test (VSST) decreased from 2.1 to 0.21 lb./gal after adding 1 lb./bbl of laponite. It was observed that the apparent viscosity (AV) and yield point (YP) increased by 16% and 33% after adding 1 lb./bbl of the laponite respectively, while there was no change in plastic viscosity (PV) which resulted in increasing the YP/PV ratio which is a good indication of fluid stability and better hole cleaning performance. For the filtration properties, there was no significant change in filter cake thickness and filtration volume.