Gypsum (Gyp) Muds are water mud system which 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 inhibit shale swelling. Gypsum, CaSO4·2H2O, content is measured by an API test, and more can be added as needed. A calcium tolerant clay deflocculant may be needed to control viscosity. Carboxymethylcellulose (CMC) and starch are used for fluid loss control along with a small amount of prehydrated bentonite.
The strengthening of environmental regulations around the world has changed the way service companies and their customers view the provision of drilling fluids. Ignoring the effects on the environment from mixing, transporting, cleaning, re-using and disposing of mud and cuttings is no longer an option.
Water-based drilling fluids, regardless of the name assigned to them, usually contain clays, water soluble chemicals (including salts), a pH control additive (hydroxyl source), and one or more organic polymers, surfactants, and deflocculants.
A major component in drilling operation success is drilling fluid performance. The cost of searching for hydrocarbon reserves becomes more expensive when drilling occurs offshore, in deep water, and in hostile environments. These drilling environments require fluids that excel in performance. Measuring fluid performance requires the evaluation of all key drilling parameters and their associated cost. Simply stated, the effectiveness of a fluid is judged by its influence on overall well cost. This chapter discusses the various fundamentals of drilling fluids and their performance in assuring a safe and expeditious drilling operation at minimum overall cost.