The bentonite used for drilling fluids, grout and sealants is primarily mined in the area encompassing Wyoming and surrounding areas in the western United States. This sodium-based bentonite is an ore whose major constituent is the clay mineral, sodium montmorillonite. Montmorillonite is a three-layer mineral consisting of two tetrahedral silicate layers sandwiched around a central octahedral aluminate layer.
In a perfect world, drilling fluids for each project would have exactly the right properties for the job at hand and the work would go as planned. But, sometimes, changing conditions downhole—e.g., shale, rock, sand or salt—require further modification in water loss properties, rheology control or viscosity modification.
In normal mud rotary drilling, it is not unusual for solids content to approach 20 percent of returns during fast-hole drilling. This is good; it means fast penetration and thus, a quicker, more profitable hole. The trick is to get the solids out of the mud before it is returned to the hole.
