Water-based Drilling Fluids
Drilling fluids have never been so popular or critical to the industries with which most of us are involved as they are today. These markets include the water well, environmental, mining, horizontal directional drilling, and limited oil and gas. The dynamics of the well or borehole continue to get more and more complicated as the types of drills used today have much greater capabilities. Today's drills have the ability to drill larger and deeper holes - in less time - than previous drills. In addition, they have the ability to drill through most types of formations at varying angles. All these complexities have made drilling fluids of the utmost importance to successfully utilize the state-of-the-art drills and complete the bore in an economic timeframe.
Within the aforementioned industries, the type of fluids this article addresses are water-based fluids. This means that all the fluids will use fresh water for their make-up water, as opposed to oil- or salt-based muds, which are used mostly in oil and gas drilling. As you have heard on a regular basis, the quality of your make-up water is important. Since 95 percent to 99 percent of your fluid consists of water, it is critical that the water comes from a good source, has a low calcium content (<200 ppm) and has a pH in the range of 8-9. If the water is from a good source, and it has a high level of hardness (calcium) or low pH, then you can simply treat the water with soda ash at concentrations between 0.25-0.5 pounds per 100 gallons.
Types of drilling fluids and additives commonly used:
- Bentonite - High-quality Wyoming sodium bentonite.
- Partially hydrolyzed polyacrylamide (PHPA) - Liquid or dry polymer used with or without bentonite to increase viscosity of fluid and inhibit clay and shale from swelling and sticking.
- Polyanionic cellulose (PAC) - Liquid or dry polymer used with or without bentonite to increase stability of borehole in unconsolidated formations.
- Drilling detergents - Surfactants used with bentonite drilling fluids to decrease surface tension of soils encountered.
- Sodium carbonate (soda ash) - Additive that raises pH of water and precipitates calcium out of the water.
There are many other types of polymers and additives that are available to the industry. However, these five fluids/additives constitute the majority of fluids used today.
Keeping mud formulas fairly simple and easy to understand, regardless of your drilling application or the formation you expect to encounter, is important. A good rule of thumb: in fine soils (clay and silts), use a polymer or polymer/bentonite system; in coarse soils (sand and gravel) use a bentonite or bentonite/polymer system. The table above covers most types of formations and drilling conditions encountered.