CommScope ConQuest Conduit Construction - Manual (Page 27)

Fluid
There is no universal soil therefore there is no universal drilling fluid. Drilling fluid provides soil stabilization, lubrication,
a means to carry away the cuttings, and suspend cutting when fluid is not in circulation. To achieve this requires the
proper blend of material for the type of soil(s) being drilled through. Your material supplier should be able to provide
you with appropriate mix rates of the various materials to achieve this.
Before the materials can be mixed with water, the water must be treated for calcium and pH. Soda ash needs to be
added at 1-4 Ibs/100 gallons. Soda ash will decrease the calcium (hardness) and increase the pH. Water hardness
should be ≤50ppm. Soda ash will also increase the pH of the water. The water pH should be 8.5 to 9.5. This is the
most important step to assure optimal hydration of the bentonite and polymers.
Bit/Reamers
There are many options on bits and reamers.
Wider blades can be used for better steering in soft ground. In hard ground, stepped or tapered carbide bits may be
better. Bits are designed with replaceable carbide inserts for rock (or soil that wants to act like rock). The point is that bits
can be matched to the soil type.
At the exit point, observe the condition of the bit to see if any changes need to be made to the fluid or reamer selection.
For example, if a bit is balled up with clay, a wetting agent probably needs to be added to the fluid to prevent stickiness.
A reamer that will chop up the clay to prevent large pieces from bridging off behind the reamer may be needed. If any
unexpected rocks are encountered, it may be necessary to use a fluted or spiral reamer to press them into the side of
the borehole. Bit/reamer selection and possible fluid changes are all dictated by the soil.
Volume
All the right decisions up to this point could be made and still have a failure by not pumping enough fluid. In a non-
reactive soil such as sand, it may be possible to produce a flowable slurry with as little as 1 to 1½ gallons of fluid per
gallon of soil, especially on short shots. This can be done because sand is inert. It doesn’t swell. It doesn’t get sticky.
Clay on the other hand, can do both. Because of this, 3 to 4 gallons or more of fluid may be required per gallon of
clay soil in order to maintain flow.
There’s not a universal soil. Because of this fact, there’s not a universal fluid, bit or reamer. Nor is there a universal
volume of fluid to be pumped per gallon of soil. Everything is interrelated.
*Source Cited: ‘The Drilling Square’ published by Baroid.
Underground Installation Methods 4.9
The Drilling Square