Page 230 - Trenchless Technology Piping Installation and Inspection

194 Cha pte r F i v e

and lubrication (reduction of friction) for drill rods tools and product
pipe. The impact of HDD on the environment, including potential reg-
ulatory problems, and associated misunderstandings, typically involves
the use of drilling fluids. An awareness of the function and composition
of HDD drilling fluids is imperative in producing a permittable and
constructable HDD crossing design. Drilling Fluids in Pipeline Installa-
tion by Horizontal Directional Drilling is a detailed discussion of drilling
fluids relative to HDD installations (Hair, 1994).
In a recent study by the Gas Technology Institute, it was reported
that inadvertent drilling fluid return occurs in the majority of HDD
operations. Since this event often cannot be prevented, prior to con-
struction, the contractor should prepare for inadvertent drilling fluid
return, as discussed in the “Inadvertent Returns” section below.

Composition
The primary component of drilling fluid used in HDD pipeline installa-
tion is freshwater. In order for water to perform the necessary functions,
a viscosifier is typically added to modify its properties. The viscosifier
used almost exclusively on HDD installations is naturally occurring
bentonite clay. The properties of bentonite used in drilling fluids are
often enhanced by the addition of polymers. This enhancement typi-
cally involves increasing the yield (i.e., reducing the amount of dry
bentonite required to produce a given amount of appropriate drilling
fluid). For use in drilling fluids, standard bentonite yields in excess of
85 barrels of fluid per ton of material. The addition of polymers can
increase the yield to more than 200 barrels per ton of material.

Mixing Water
It is standard practice on an HDD river crossing to draw water for
drilling fluid directly from the waterway. Where sufficient amounts
of freshwater are not available, water may be obtained from a nearby
municipal source or hauled to the crossing location. Substantial
amounts of water are required; therefore ample trucking and storage
are critical, if water must be hauled to the site.

Disposal of Excess Drilling Fluids
The preferred method of disposal for excess drilling fluid on an HDD
installation is dispersal at the drill site. As an alternative, excess fluid
may be hauled to a remote disposal location. Disposal of excess drill-
ing fluid in a waterway is not recommended and may not be allowed
by regulatory agencies. The methods of disposal applied to a specific
crossing will be dependent upon the size and location of the crossing
as well as any applicable local, state and national regulations, and
may include:

• Land farming––spread over an open area and mix with native
soil