Regardless of whether one is drilling a foundation drilled shaft, vertical well or doing a horizontal directional drilling project, contractors require a lot out of a drilling fluid or slurry. Functions of a drilling fluid include cooling and lubricating the hole and bit, cleaning the hole, suspending and transporting cuttings, holding the hole open, stabilizing the hole, controlling fluid loss, loss circulation and frac-outs, reducing torque associated with sticky soils, and controlling sub-surface pressure.
In knowing all of the functions of a drilling fluid or slurry, it is ironic how some contractors simply dump bentonite into untreated water and expect the fluid or slurry to flawlessly perform all of these functions. This article is a focus on borehole stability. Understanding how a drilling fluid or slurry stabilizes a borehole can dramatically increase odds of success for drilling contractors.