| Vl. DRILLING SLURRY
- CONTAINMENT, RECYCLING AND DISPOSAL
A. BACKGROUND
- The directional crossing process requires the use of large volumes
of slurry that provide the following functions:
1. Hydraulic cutting with a jet.
2. Provide energy to the drill motor.
3. Lubricate the cutting head.
4. Transport drill cuttings to the surface.
5. Stabilize the hole against collapse.
6. Guard against loss of slurry into surrounding formations.
B. SLURRY COMPOSITION -The slurries most commonly used are bentonite
based. Bentonite is a naturally occurring Wyoming clay known for its
hydrophilic characteristics. Often polymer extenders are also added
to enhance certain characteristics. Material Safety Data Sheets (MSDS)
are readily available from suppliers and can be presented to regulatory/disposal
authorities.
C. CONTAINMENT - The slurry is pumped down hole and circulates
back to the surface and collected in "return pits." These pits typically
have a volume of at least 500 cu ft. Depending on the nature of the
project, the slurry is pumped from the return pits to a "settling and
containment pit." These pits vary in size depending on pumping rates
and contain the slurry for recycling or disposal.
D. RECYCLING SLURRY - Slurry that has been circulated down hole
and collected in the containment pit is then passed through machinery
that separate the cuttings from the slurry. This process involves a
series of shaking sieves and various size hydroclones.
E. SLURRY AND CUTTINGS DISPOSAL - Significant amounts of slurry
are normally disposed of at the end of a project. Economics for disposal
is extremely site specific. This slurry can be disposed of by:
1. Use at another drilling location.
2. Spread onto raw land for water retention improvement.
3. Evacuate to a dump site.
If working in an area of contaminated ground, the slurry should be tested
for contamination and disposed of in a manner which meets governmental
requirements.
F. COST MITIGATION FOR THE OWNER - With pre bid planning and
research, the owner can realize significant savings in slurry disposal.
It is in the owner's interest to define and specify all disposal issues.
In particular:
1. Define an approved disposal site as part of the project specifications.
2. Because it is difficult to estimate disposal quantities, disposal
should be a separate bid item as either "cost plus" or on "unit rates."
3. Inadvertent returns are not uncommon and difficult to predict. The
issue should be fairly represented to permitting bodies prior to construction.
Contingency plans for containment and disposal of inadvertent returns
should be priced as a separate bid item and agreed prior to construction.
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