Assisting
Directional Drilling With Pneumatic Pipe Rammingby Jim Schill
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Drill Stem RecoveryThe principal is the same during a drill stem recovery as it is during bore salvage, however, there are two possible tool configurations. Depending on the situation, contractors can remove the drill stem from the ground or, if the stem is still attached to the drill rig, push on the stem while the drill rig pulls back (See Figure B).
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Pullback Assist
The pullback assist technique works directly on getting the product pipe installed. Drilling underwater or in loose flowing soil conditions a condition known as hydrolock can occur. Hydrolock occurs when the external pressure being put on the product pipe from ground water pressure, drilling fluid pressure and/or soil conditions exceeds the drill rig’s pullback capability or the product pipe’s tensile strength. The percussive action of a pipe rammer in this situation is used to help free the immobilized pipe.
The pullback assist technique has been successfully used on steel pipe, as well as HDPE. The technique can be used as a safety measure in anticipation of hydrolock problems or after the pipe has become immobilized (See Figure C). Time is a key factor with any of these methods. The rate of success improves the faster problems are responded to. To improve response time, many drilling contractors are now bringing ramming equipment to directional drilling sites in order to respond quickly to problems if they develop.
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Conductor
Barrel
The
Conductor Barrel process differs slightly from the other
three methods in the sense that it deals with the actual
drilling aspect of the project rather than pullback or recovery.
The concept behind the Conductor Barrel is creating a clear
pathway through poor soil conditions so that drilling can
begin in more preferable soil conditions. The success of
a drilling operation can often be determined right at the
start. If drilling does not begin in soil that is conducive
to drilling, the success of the entire project can be put
in jeopardy. Loose, unsupported soils are prime candidates
for the Conductor Barrel method.
During the Conductor Barrel process, casings are rammed
into the ground, at a predetermined angle, until desirable
soil conditions are met. The spoil is removed from the casing
with an auger or core barrel. Drilling proceeds within the
casing in the desirable soil conditions. In addition to
assisting drilling operations at the start, the conductor
can also serve as a friction-free section during pullback
(See Figure D). In addition, the conductor barrel can prevent
situations in unstable soils where drilling fluids under
pressure force their way into waterways or wetlands, acting
in a similar fashion to containment cells.
Drilling contractors throughout North America have successfully
employed all four directional assist techniques.
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Case Study:
Pullback Assist on Gulfstream Pipeline Project
Laney
Directional Drilling, Inc., Humble, TX was working to meet
an aggressive timeline on the Gulfstream Pipeline project
off the coast of Alabama when the crews were put to the
test by extremely difficult directional drilling conditions
during the installation of two major sections of the pipeline.
To solve the problems Laney crews combined the power of
their self-manufactured LDD Series directional drill rigs
with the percussive action world’s largest pipe rammer,
the Grundoram Taurus from TT Technologies, Aurora, IL (part
of the international group of Tracto-Technik companies).
Gulfstream
Project
The
753-mile Gulfstream natural gas pipeline begins near Mobile,
AL and reaches Florida in Manatee County, traveling a majority
of the way under the Gulf of Mexico. Laney Directional Drilling,
Inc. was sub-contracted by Stolt Offshore, Inc., Middlesex,
UK for several directional bores in various locations along
the pipeline route. Some of the most difficult bores took
place where the pipelines transitioned from offshore to
onshore, under a shipping channel, in the Gulf of Mexico
off the coast of Bayou LaBatre, AL.
The Bayou LaBatre section called for the completion of two
4,700-ft parallel bores for the final phase of the project.
The 36-inch diameter epoxy coated steel product pipe had
a 1.25-inch wall thickness. The pipes needed to travel under
a shipping channel in the Gulf of Mexico to a location onshore.
One line would serve as the main line, the other as the
supply line.
The Laney crew set up on shore to drill the pilot bore out
to the pre-determined spot in the Gulf of Mexico for the
installation of the first pipe, the main line. The second
bore would install the supply line. Over the course of several
weeks the Laney crew set up, performed the necessary survey
work, and completed the pilot bore and a series of backreams
in preparation for pulling back the pipe.
Pullback
Directional drilling operations under water face distinct
challenges. Difficult soil conditions under river bottoms,
lakes and even an ocean combined with the weight of the
pipe and the hydrostatic pressure of the water itself can
create problems during drilling applications. Reaching a
point during product pullback where the pulling forces required
to pull in the pipe exceed maximum capability (a condition
often referred to as hydrolock) is one potential problem.
These were the challenges the Laney crew faced as they began
pulling back the 4,700 feet of 36-inch diameter steel pipe.
The pipe lay underwater and was hoisted to the surface,
connected for pullback and then lowered back down. Pullback
started slowly, but continued until approximately a third
of the way through. The Laney drill rig began to reach the
upper end of its pulling capabilities. The decision was
made to stop the pullback and try and recover the pipe.
After recovering the pipe with a cross-winch anchored off
shore, the Laney crew began pullback a second time. The
second pullback halted near the 4,000-ft mark. After a meeting
with Gulfstream officials, it was concluded that the supply
line was more important to keeping the project on schedule.
So, the decision was made to begin work on installing the
supply line.
While the Laney crew started moving equipment into position
for the second bore, TT Technologies (part of the international
group of Tracto-Technik companies) was contacted and a 24-inch
diameter Grundoram Taurus
pneumatic pipe rammer was brought on site to assist with
the project.
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Pullback
Assist
When the Taurus pipe rammer arrived at the site, the supply
line pullback was ready to begin. The decision was made
to ready the rammer to assist during pullback. Pullback
of the second pipe proceeded to within 800 feet of completion
when pullback stopped again.
The rammer was taken to an awaiting work-barge in the Gulf
by another barge equipped with a large crane, pipe adapter
and large air compressors. Once at the work-barge, the end
of the product pipe was carefully lifted with the crane
and rested on the surface work-barge. The end of the pipe
was fitted with the specially fabricated adapter that connected
to the 24-inch diameter Grundoram Taurus,
completing the assembly.
With the Grundoram in
place, the crew pulled with the directional drill rig.
The rammer was started and within a few minutes the pipe
began to move. The hammer and drill rig worked in tandem
until the section drill stem needed to be removed. The
crew shut the rammer off, removed the 31-ft section of
drill stem and started pulling again. The rammer assisted
for a few more minutes, then the rig was able to complete
the pullback on its own. The second bore was complete,
but the first bore was still waiting, immobilized for over
21 days
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Push & Pull
Despite sitting for three weeks, everyone was optimistic
about getting the first pipe all the way in the ground.
The crews repositioned the drill rig and moved the barges
out to the end of the first pipe string. Again the end of
the pipe was carefully lifted out of the water and the Grundoram,
pipe adapter and pipe were fitted together.
The crew started the drill rig and pulled back at approximately
50 percent power. Then the hammer was started and the crew
let it run for a few minutes. When they believed that the
energy from the rammer had moved through the pipe string,
more pulling force was applied and the pipe began to move
and was ultimately installed successfully.
World Pipelines, April 2003