What Does Weighting Agent Mean?
A weighting agent is a material that, when added to drilling fluid, increases its density. The most commonly used weighting agents in the drilling industry are barite and hematite, which meet specifications by the American Petroleum Institute (API) and the International Organization for Standardization (ISO). Weighting agents are added to drilling mud to maintain sufficient bottomhole pressure (BHP) and prevent the undesired influx of formation fluid, known as a kick.
Trenchlesspedia Explains Weighting Agent
The widely used weighting agent barite has a minimum specific gravity of 4.2 g/cm3. Hematite is denser, with a minimum specific gravity of 5.05 g/cm3. The primary role of weighting agents is controlling formation pressure and maintaining wellbore stability. If BHP is not sufficient, a kick can occur, allowing formation fluids to flow into the wellbore. This can cause a blowout from pressured formation fluids, which can be dangerous.
Barite is a standard weighting agent because of its high specific gravity, which can produce mud weights in excess of 19 lb/gal. Barite is hard enough to reduce it to a particle size that reduces losses on the shaker screen and minimizes settling of cuttings in the drilling fluid. Another benefit of barite is that it is inert enough to be used in drilling fluids that have different chemical constituents.
Ilmenite and hematite are other weighting agents that are used, but their higher specific gravities cause problems in the drilling fluid rheology and settling rate. Their greater hardness has an abrasive effect on the equipment, and their magnetic properties (due to the presence of iron oxide) can affect the function of drilling equipment.