Bentonite based drilling fluids are used in both vertical and horizontal drilling. The desirable drilling fluid properties, however, are different. A drilling fluid property that is desirable in vertical drilling may be detrimental or used differently in HDD.
Viscosity is the measurement of the thickness of a fluid. It is measured with a Marsh Viscosity Funnel and is reported in seconds per quart. Viscosity measurements are important in HDD but are important for different reasons than in vertical drilling. Viscosity is something of a necessary evil in HDD.
Gel strength is the measurement of the suspension properties of a drilling fluid. Gel strength is measured with a rheometer or shearometer and is reported in pounds per 100 square feet. Gel strength is of the utmost importance, especially in coarse-grained soils (sand, gravel and rock).
Fluid density is not a concern as it is in vertical drilling when related to hydrostatic head. Because of the relatively shallow depths at which HDD installations are made, hydrostatic head doesn’t come into play.
PH is an indicator of water quality and is used the same as we should be using to test water quality in all drilling practices.
It is important to remember that, although we are using much the same materials in both vertical drilling and HDD, we have different needs as far as fluid properties are concerned. These properties are adjustable. Let’s adjust them to be beneficial rather than detrimental.