One of the most overlooked aspects of mixing drilling fluid and grouting products is the pre-treatment of the mix water. Because water makes up 80-97 percent of the slurry, it should always be a priority to make sure you have good water before you start mixing. Few contractors take the time or effort to pre-treat the water to make sure they are getting full utilization of the drilling fluid or grout. I often hear contractors comparing various manufacturers' bentonite products and discussing how one product just did not mix as well as another. Chances are that the difference is in the make-up water.
The ideal pH for mixing bentonite is between 8.5 and 9.5. Most municipal water has a pH of 7, which is neutral. One of the most common mistakes I find in the field is that people believe the water they get out of a water hydrant is good for mixing, so they very seldom check the pH. If they did, they would find that the pH is usually around 7 and should be treated before they try to mix up their drilling fluid. If mix water is taken from streams, ponds or other sources of surface water, the pH can be below 6.5, indicating hardness.
Understanding pH is important because water hardness can be detrimental to the yield of bentonite. Pre-treating the make-up water with soda ash can raise the pH to an ideal level and precipitate out the minerals causing the hardness. Soda ash is the common name for sodium carbonate, which precipitates soluble calcium by separating into sodium and carbonate ions in solution.
In horizontal directional drilling (HDD) applications, high gel strengths are essential to the success of the bore. Some specialty HDD fluids have the soda ash, bentonite and polymer all together and are designed to have almost three times the gel strength of a straight high-yield bentonite. Due to the presence of soda ash in the mix, these products can be used with low-pH mix water (not too low) if the contractor is at a secluded site and does not have the ability to raise the pH. In an attempt to save money, some contractors try to use high-yield bentonite and usually do not pre-treat the water with soda ash before mixing. Therefore, they wind up with a lower gel strength than high-yield mixed under ideal conditions. This lack of gel strength can lead to the cuttings being left in the bore hole and packing off around the drill string, causing frac-outs and stuck pipe.
It is very easy to spot a tank of mud mixed with untreated water: just look for clear water at the top of the tank and a pile of mud at the bottom. Sometimes it pays to remember that basic actions can save us time and money. If you start with bad water, you'll wind up with bad drilling fluid, so pre-treat your water with soda ash.
