Horizontal Directional Drilling
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Directional
Drilling has seemed to be the most preferred method for pipeline construction
as of late. The reason being that Directional Drilling can be installed without
any disturbance to natural habitats.
Directional
Drilling has the least environmental impact of any method of construction. By
Directional Drilling you are able to be a great deal of depth below the
obstacle, providing minimal maintenance cost and up keeping maximum protection.
In some cases, Directional Drilling can cost a lot less then most other
construction methods and procedures.
STEP
1 – PILOT HOLE
The
pilot hole is the beginning of the Directional Drill crossing. The Pilot hole
is achieved either by excavation by jetting or by a down hole motor. Depending
on the condition of the soil the pilot is drilled along a pre-determined
alignment in which the path is selected by traditional methods.
The
typical pilot hole on most large rigs is 9 7/8 but can vary depending on the
soil conditions and rig size. Drilling fluid is pumped through the drill pipe
to the drill head at which time it is jetted through or pumped through a drill
motor. The end of the Drill Pipe is to core the pilot hole. The drill fluid
lubricates the drill stem and carries out the cutting to the surface.
The
drill fluid is then recycled and re-injected into the drill stem. The pilot
process can take several days, depending on the condition of the soil and may
require changing of the drill stem or drill head.
STEP
2 – REAMING PROCESS
Once
the pilot hole has been completed the 2nd step takes place with a reamer, or
hole opener. The hole openers come in different shapes and sizes and vary
depending on the soil conditions and density of the soil; typically a fly
cutter is used in good ground conditions.
The
reaming pass is done in several steps depending on the size of the hole,
(example: 42″ finish hole would be 3 to 5 different ream passes 14″, 20″, 34″,
42″). The reamer is attached to the drill string and is rotated and pushed or
pulled while rotating and drill fluid is pumped to the reamer through the drill
pipe. The excavated soil is suspended in the drill fluid and then brought to
the surface and recycled.
When
the reamer is attached to the Drill string there will always be a drill pipe on
both sides of the reamer allowing for the drill string to be in the hole at all
times. The reaming process can take a significant amount of time depending on
the condition of the soil.
STEP
3 – MUD PASS
After
the desired hole has been achieved and the reamer has passed through it
completely, a mud pass or packer reamer will be done to assure that the hole is
clean of all excavated material and that the drill fluid has filled the hole
completely, to allow for a smooth lubricated pull back of the pipe, avoiding
friction of the pull section.
STEP
4 – PULLBACK PROCESS
The
final step now is when the pipe is pulled into the reamed hole. A weld cap is
installed on the pipe where a swivel is placed attaching the drill string, thus
not allowing any rotation of the pipeline. Depending on the size of the pipe an
artificial buoyancy measure might be taken. This is to keep the pipeline as
close to neutral buoyancy. If no measures are taken several problems may occur
(example: coating damage from pipe floating in drill fluid and causing excess
friction causing more pull). Most typically buoyancy control is done with
pumping water into the pipeline through P.V.C. pipe and checking the gallons
pumped.
At
completion of directional drill, demobilization and clean-up takes place.
Sumber: http://www.southeastdrilling.com/drilling/
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