Science Of Mud, Systems In HDD Ops

March 2012, Vol. 67 No. 3

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,” says Heinen. “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.”

The mathematics of mud
As mentioned earlier, bores can fail due to a poor quality fluid mix, but also bores fail when the standard procedures and accepted formulas for fluid-to-soil ratio are not followed. There is a formula that must be followed to determine the amount of mud needed for effectively maintaining the bore path, which figures in the bore diameter, soil conditions and process.