Science Of Mud, Systems In HDD Ops

March 2012, Vol. 67 No. 3

The old adage “don’t muddy the water” doesn’t apply to horizontal directional drilling (HDD) where the water is supposed to be muddy. Drilling fluid (mud) extracts particles and cuttings from the bore hole, as well as stabilizes the hole itself. Mud has always been an essential element to a successful drilling operation.

Along with the drilling fluid, a reliable method of delivery to the drill is needed. This is called a mixing system or mud system. The mud system delivers the fluid to an onboard pump (on smaller horizontal directional drills) or a standalone pump that feeds into a larger rig (generally 100,000-pound capacity or larger.) With the rise of mud recycling in drilling, reclaimers are becoming more prominent on jobsites. These are a type of mud system that “cleans” the used mud and recirculates it back into the mixing system to be reused. An HDD contractor needs to make sure to use the right kind of mud and the proper equipment to effectively supply the correct amount of fluid into the pump and downhole.

“The mud system is the device on the jobsite that is married to a particular drill rig,” says Jon Heinen, pipeline segment manager for Vermeer Corporation. “Its job is to provide that rig with the appropriate amount of drilling fluid, so it has to be a good match. A large pipeline project with a maxi rig is going to have a significantly different system than that of a smaller 9,000-pound (thrust/pullback) machine. Either way, all HDD machines need a mud system of some kind.”

There is a method to the “mudness,” and strict adherence to procedures needs to be followed. The key factors are proper planning, ensuring the use of proper equipment and consistent drilling fluid maintenance during drilling operations.

Drilling fluid, mud, slurry -- it’s all the same
“Mud” is the common reference to drilling fluid used in all types of drilling operations. “Slurry” is another term that is an interchangeable reference to drilling fluid. Mud serves multiple purposes such as: provide coolant for down hole electronics; suspend and displace cuttings from the bore hole; reduce wear on downhole tooling; and aid building a stable bore hole by reinforcing and maintaining the walls of the bore or tunnel. Given the importance of mud, achieving the right mix is another science.

“There is no universal formula,” says Heinen. “There’s no perfect recipe for a fluid mix. It just depends on what you’re doing, where you are and how each soil encountered reacts, since soils react differently.”