Bentonite is the primary additive that forms the composition of freshwater-based drilling muds and controls the fluid loss and flow properties of the mud. The presence of a sufficient quantity of high-quality bentonite in the system is the primary requirement for forming a thin, strong, and impermeable filter cake. These filter cake properties are critical in terms of preventing drill string sticking and formation damage. The bentonite used in the spud and lignosulfonate muds recommended in this program must meet the requirements specified in API Spec 13A, Section 4.