Some in the horizontal directional drilling (HDD) industry refer to the appearance of drilling fluid in a place other than intended as a “frac out.” The term can be confused with “frac’ing,” however, which refers to the hydraulic fracturing technique used for production-well development. Tyson Smith, an authority on HDD drilling fluid, said the similarity of expressions is an unfortunate coincidence.
Smith conducts mini seminars for contractors, fluid distributors and other drilling professionals. A former “mud engineer” in the oil production industry, he has been providing Wyo-Ben customers onsite consultation since 2006 for their HDD, water well and tunneling projects. Wyo-Ben is not only one of five top bentonite clay suppliers in the country, but also provides a wide range of innovative solutions specifically designed for HDD.
The proper term for the unexpected appearance of drilling fluid, Smith said, is “inadvertent return” (IR). IR is relatively common he explained, and generally harmless – with certain exceptions.
Drilling Fluid Return
In fluid-based HDD drilling, operators send a drilling fluid down the hollow interior of a drill string. The fluid’s primary purpose is flushing cuttings from the bit and carrying them away. It also reduces the force necessary to move drill string and lowers the risk of getting tooling or pipe stuck in the hole.
Additives such as bentonite clay earn drilling fluid its nickname, “mud.” Bentonite-based drilling fluid has a slick, gel-like consistency. The fluid is meant to return to the surface along the “annulus,” the space between the drill string and the bore wall. IR means the fluid has gone somewhere else.
IR Prevention, Mitigation
The simple formula for preventing IR in most cases, Smith said, is based on containment pressure. “When the formation’s containment pressure is greater than the pressure in the hole, the fluid stays in the hole.”