Guar and guar derivatives are used as viscosifiers and fluid loss control additives in low solid drilling muds. The most important property of guar is its ability to develop viscosity in fresh water or brine. Guar and HPG are effective fluid loss control additives due to their colloidal nature and high molecular weight. Typical use levels are from 0.14% to 0.57% by weight for viscosifying and filtration control.
The hydration of guar and HPG in drilling fluids is dependent on pH, temperature and shear. Guar and HPG hydrate faster in the pH range of 6 to 8 but will also hydrate in an alkaline mud although at a slower rate. Guar and HPG have been employed successfully in foam drilling applications using a stiff foam viscosified with guar or HPG. Use levels are from 0.07% to 0.29% by weight.[divider]