"If you're trying to understand a particular soil condition such as sand, identify if it's wet and running sand or dry and compacted," says Savage. "Time of the year can also influence soils. In the Midwest, the summer months can be dry, so our clay can get very hard. But it's a different animal in the Spring and Fall when there's more moisture available. You will want to ensure you're talking about the same depths, since soil changes at various depths."
It can be beneficial to dig down a few feet and do your own visual inspection, as well. "Also pay attention to the initial cuttings coming from the pilot bore," suggests Tom Tibor, Baroid Industrial Drilling Products. "It can reconfirm your thoughts or serve as an initial check."
Mud mixes broadly fall into two categories: bentonite mixes designed for coarse, non-reactive soils, such as sand, rock and gravel; and polymer-based mixes for fine, reactive soils such as clay and shale.
For unstable soils such as sand, bentonite mixes build a wall around the tunnel to prevent water loss and intrusion, so the hole will stay open long enough for the tooling and product to pass through uneventfully. "This will also help reduce torque and pullback requirements," says Savage. "If that soil caves in or comes around the product you're pulling in, it acts like a piece of sandpaper when you wrap it around a steel rod. It grips down on it and locks up so you can't pull it or rotate it."
Plus, you can't get spoils out, adds Nameth. "You should be able to recognize rotary torques going up by watching the gauges," he notes. "And you will notice that it's getting harder to turn. At that point, stop. Don't keep drilling yourself into problems. You might get lucky and get through the pilot hole, but you will likely have problems on the ream. The hole may collapse entirely and you may lose tooling and drill pipe."
Fluid mixes are designed to combat the tendency clay soils have to swell and get sticky when hydrated with water alone. "Clay can swell up to 10 times its original size," says Savage. "It can settle around the drill stem and product pipe and lock it up so you can't move it. Polymers keep the clay from swelling and they also add a lot of lubrication to make the tooling spin and pull easier."
It's also important to identify properties of any water you use for mixing additives, notes Tibor. "Some water - even city water - may have a low pH with a lot of calcium," he says. "That can affect the ability of the additives (bentonite and polymers) to mix properly and be utilized to their full extent."
In that effort, Tibor encourages contractors to test the water for pH and hardness. In general, soda ash should be mixed into the make-up water to raise the pH and reduce excess calcium. The soda ash assists in creating an environment that will enhance the yield and performance of selected fluid additives and optimize drilling fluid properties. It also is key in minimizing any waste of the fluid additives due to not mixing completely.
Drills rigs equipped with more than one fluid tank can prove beneficial. "That gives you the ability to mix in one and use the second one to supply the drill," Tibor says. The alternative is to stop drilling once you've used the fluid in the single tank, fill the tank with water and additives, then mix everything. "That takes time. And for optimum benefits, you should wait 15 to 20 minutes for the fluid to mix properly."
Oftentimes what happens is that contractors don't want to wait. "They mix on the fly. They keep drilling - fill the tank with water and mix," says Tibor. However, until the additives and water are thoroughly mixed, they are basically pumping water.
"Plain water doesn't have the properties you need for boring. It doesn't have the ability to suspend the cuttings that you create when you drill," Tibor points out. "And if you don't remove enough of the cuttings, you can get stuck, stretch the product, fracture the surface or hump the road because there simply isn't enough room for the product to fit. You don't save money by trying to get by without any mud. Fluid should be considered a tool, just like a bit or reamer."
Nameth agrees, noting, "It may be tempting to try to get away with minimal amounts of fluids or just water alone. That may work in small-diameter installations. But when you step up into installations above about 6 in., fluid management becomes more important.