The game changed 25 years ago for the horizontal directional drilling (HDD) industry with the introduction of a dual-pipe, rock drilling package. This All Terrain (AT) technology means operators have an option outside of powering the drill bit primarily with drilling fluid through the use of a mud motor.
Mud motors are still a common tool found in the HDD industry. They take drilling fluids that are pumped downhole, through the drill string, at high volumes, into a rotor and stator and transfers that into mechanical power that drives the rotary bit on a mud motor. Mud motors are high-fluid volume downhole tools that can produce high drilling fluid pressures downhole and increases the possibilities of inadvertent returns. Inadvertent returns happen when the drilling takes the path of least resistance to the surface and does not follow the designated path of the bore and makes its way through to the surface in unwanted areas.
Mud motors can often send much more fluid downhole than is actually needed on the job. A bore that requires 20gpm of mud-flow to efficiently flush the bore of cuttings, for example, ends up using an additional 180gpm of fluid to run the mud motor. And, as the drill units become larger or the ground harder, mud motors can send as much as 10 times more mud downhole than what is needed to clean the borehole.
The additional drilling fluid results from inefficiencies of creating mechanical power. To accumulate enough energy for the drill bit, mud often flows over a 15 to 30ft power section. On average, only 50 per cent of the power generated makes it downhole. In comparison, 95 per cent or more of the HDD unit's inner drive power is successfully transferred downhole using AT systems.
A switch from powering the bit with drilling fluid to All Terrain technology helps operators minimise how much fluid is pumped downhole. And AT systems provide a way to use the HDD unit's power more efficiently for driving the drill bit.
This is possible because of the dual-pipe technology offered by AT systems. With an inner drive shaft that reaches back to the HDD unit, these motors physically control exactly how much horsepower is sent to the bit.
By reducing operator reliance on drilling fluid, AT technology is a more efficient power option.
This direct connection to an HDD unit also reduces the overall size of an AT system. Instead of a long power section, AT systems are between 3 and 5ft long. And by placing the electronic locating package in the middle of that system, the shorter length puts the package 1 to 2ft behind the bit. Locators are then able to more accurately track the location of the drill bit's cutting face, instead of predicting where the bit could be when the electronics package is embedded behind a mud motor's 15ft power section.
A small footprint is becoming a more and more common requirement on HDD job sites. AT technology generally provides a smaller footprint job site than mud motor-driven job sites, partially due to having to use much less fluid. Large volumes of fluid usage on the job site comes with larger tanks and larger reclamation systems with a mud motor.
Sometimes technological advances don't generate a huge impact, but that is not true for AT technology. The dual-pipe system lets operators control how much fluid is used on varying job sites. And, by keeping drilling fluid to a minimum, HDD crews can decrease the risk of inadvertent returns and stay efficient and profitable on any job site.