Cable Tool
Drilling
GeoCore
maintains a full fleet of equipment designed to allow us the capability
to perform a wide variety of tasks. One of our specialized areas
is cable tool drilling. There are two types of cable tool
drilling: drive barrel and percussion paddle bit.
Drive
Barrel Method
 GeoCore
is one of
only a few private companies in the Midwest who offer drive barrel
drilling. The
drive barrel method of cable tool drilling offers the advantage of less
fluid and solid waste handling and more efficient development. The drive barrel
technique is performed much like a standard penetration test--but on a
much larger scale. A drill casing is driven into the soil by the
cable tool rig. The soil goes into the casing and is easily collected from the drive barrel.
By it's
nature, the drive barrel method is a continuous sampling method of
drilling.
This method significantly reduces a project's waste handling costs
because it can use the minimum allowed diameter, reducing soil waste, and does
not require the addition of fluid to remove drill cuttings, reducing fluid
waste. As a result, development water is significantly
reduced.
The
drive barrel method is commonly used for the installation of Soil
Vapor Extraction (SVE) wells. Engineers
have discovered improved results using the drive barrel method over other drilling
techniques. The drive
barrel method “shears” or “slices” the strata; thus, it does not
leave smeared soils or a filter cake on the borehole wall like auguring and fluid rotary drilling
can.
In addition, the driving action tends to “open” the formation
and allows for enhanced air movement.
The
drive barrel technique is most often used in relatively dry,
unconsolidated soils such as clays, silts, sands and gravels often found
in the unsaturated zone. However,
using a combination of driving casing and the drive barrel drilling is
performed below the water table in unconsolidated soil and/or sand
environments. This also reduces waste handling costs, and well development is made easier and more
cost effective than other drilling methods.
Paddle
Bit and Bailer Method
Paddle
bit drilling is the most familiar form of cable tool drilling and can be
used in any formation but is typically reserved for rock drilling. The
percussive action of the drill bit crushes the formation. Water is added
prior to each drilling run to create a slurry during drilling. The drill
bit is removed from the hole and a bailer removes the slurry from the
hole before drilling continues. The
paddle bit and bailer method is a proven drilling technique to
penetrating hard, consolidated strata like limestone, sandstone, and
shale.
However,
samples obtained using percussion drilling are lower quality because the
cuttings are pulverized and mixed other cuttings in the particular
drilling interval. Therefore,
the samples pose limited usefulness for geological and chemical
analysis.
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