Drilling Fluids or Muds
Drilling Fluids
Drilling fluid has several functions and can be designed to suit a given set of conditions. Whilst similar to those used in pipejacking and microtunnelling the design use is often very different. Specific uses include: Lubrication and/or cooling of the cutting head and to reduce wear; To soften the ground so that it is easier to drill through; To convey spoil material in suspension out of the bore; To stabilise the bore prior to back reaming; To lubricate the product pipe during insertion; and to power mud motors for drilling through hard ground if such equipment is used.
The simplest drilling fluid is water, and it may be unnecessary to use anything more sophisticated for short bores of small diameter through good ground.
A mixture of Bentonite and water is the most common type of drilling fluid or 'mud'. In addition to simple water/bentonite fluids, there are polymer-based materials and a wide range of additives, which are used to tailor the properties of the drilling fluid to suit the soil conditions and the nature of the project. For example, the viscosity should be low enough to flow through the system at reasonable pressures, but sufficiently high to prevent significant loss into the ground.
As with pipejacking and microtunnelling, the formulation of drilling fluids is a complex science and is an area where specialist guidance should be sought, especially when dealing with difficult ground conditions. The design of mixing, pumping, filtration and recycling plant is also a major consideration, especially for large-scale projects, and again advice should be sought from experienced contractors or manufacturers.