gyp mud
A calcium-based water mud system containing gypsum. Gyp mud can be used for drilling shales, but it is also well-suited for drilling gypsum, anhydrite and salt stringers. An advantage of gyp over lime muds is that the pH of gyp mud need not be so high because it contains more soluble Ca+2 to inhibitshale swelling. Gypsum, CaSO4·2H2O, content is measured
Detailed Explanation
by an API test, and more can be added as needed. A calcium-tolerant claydeflocculant may be needed to control viscosity. Carboxymethylcellulose (CMC) and starch are used for fluid loss control along with a small amount of prehydrated bentonite.