Science Of Mud, Systems In HDD Operating Productive System

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. 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.

Rise of mud recycling
Rising costs of mud disposal and the limited availability of disposal sites are driving some HDD contractors to reuse their drilling fluid, which requires a reclaimer.

Environmental concerns are also a factor so we are seeing more reclaimers required in drilling specs. Also mud disposal is cost prohibitive and we are seeing an increase in mud recycling requirements on job sites.

Cost factors in mud disposal include hauling of used fluid, whether it is trucking or rail cars, sometimes out of state. Dumping costs are expensive; certain situations may require additional additives to be mixed with the used fluid that have come into contact with hazardous materials underground.

It is estimated that about 20 percent of what comes out of the exit pit is solids and cuttings. Mud recycling is simply using a reclaimer instead of a standard mixing system — it’s a combination of a mixing system and a system to clean dirty fluid, and then recirculate the cleaned fluid.
A standard mixing system employs a mixing hopper, an agitation system and a pump to deliver to the drill. These components are standard no matter the size and capacity of the system. The hopper is where bentonite is introduced into the clean water or clean mud. The agitation system continuously circulates the fluid to keep the components in suspension, and the pump creates the flow to deliver the fluid into the drill.

A reclaimer is generally used on drill projects when you are using a large volume of fluid. Smaller projects can utilize an excavation system and dispose of mud in a cost effective manner. A reclaimer utilizes a series of shakers, cones and screens to filter out solids from the fluid, leaving the bentonite and other additives in the solution and recirculating the cleaned fluid.

The reclaimer is generally configured with multiple tanks which can include a clean mud tank, a dirty fluid tank and a desander and/or desilter tank. Dirty fluid is drawn from the return pit and pumped across the first cut shaker(s), which sift out all the larger particles of sand and debris. Then the fluid is pumped through the desander cones where a cyclonic motion is used to eliminate even smaller particles, and again across a shaker screen equipped with a finer mesh screen to further the cleaning process. The fluid finally passes through desilter cones and again across a final set of shakers and screens, which separate out the smallest micron particles from the drilling fluid completing the cleaning process. Each deck on the reclaimer uses progressively smaller screens to remove micron-sized elements from the fluid. Once through, the fluid is stored in the clean mud tank ready to be recirculated back down hole.

You won’t get 100 percent return on your fluid due to several scenarios.There is typically some circulation loss either due to soil absorption, formation instability or the drilling process. When using a reclaimer, you should use a mud test kit to test the clean fluid being held in the clean mud tank. This test will verify both information on the cleanliness of the mud and be an indicator of how well your cleaning system is performing

Alice
brightway@bwsolidscontrol.com
86-29-89300061