Assisting Directional Drilling With Pneumatic Pipe Ramming
Some of the most spectacular trenchless projects have been accomplished through the use of directional drilling. Drill operators and manufacturers are finding new and creative ways of tackling tough projects and difficult situations by utilizing pipe ramming technology to assist directional drills.
Recently, trenchless equipment manufacturer TT Technologies, Aurora, IL introduced several pipe ramming techniques that are helping drill operators solve drilling problems and tackle tough conditions. The techniques are changing the way drillers approach projects and respond to problems on the job.
Four pipe ramming techniques are being used to help prevent failed directional drilling bores and even salvage bores. Properly configured pipe rammers can be used to salvage product pipes, remove stuck drill stems and assist drills during product pullback, overcoming hydrolock.
The first technique is used to remove a stuck product pipe are simple yet highly effective. During a bore salvage the pipe rammer is attached to the end of the partially installed product pipe. The pipe rammer needs to be attached to the pipe so that it pulls the pipe from the ground. This can be accomplished through a fabricated sleeve (See Figure A). A winch or some type of pulling device is used to assist the rammer during operation. In many cases, the percussive power of the pipe rammer is enough to free the stuck pipe and allow it to be removed from the ground.
Drill Stem Recovery
The 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).
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.
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.
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).
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.
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.
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.
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.
by Jim Schill
World Pipelines, April 2003