What is a surface casing and why do you need one? Initially, a surface casing was referred to as a conductor barrel and this terminology is widely used in the horizontal directional drilling (HDD) industry. Surface casings or conductor barrels are required to isolate unconsolidated formations (gravel and cobble layers) and to ensure full fluid return back to the rig. This unstable ground can be disastrous while drilling as this material can lock into place in the cavity created by the downhole tooling and prevent the tool from moving forward and backward. A surface casing is installed at a designed angle and driven down until it can be seated into bedrock.
The surface casing is not only important for the initial bore on the entry side, but also during the pullback of the final product pipe. The conductor barrel provides a clean hole that will not fill-in or erode during construction, and is designed based on the size of the product pipe being pulled back once the crossing has been completed. Typically a pneumatic ramming tool rams the conductor barrel into the ground, the pipe is rammed into place and another segment is welded on.
The length and depth of the surface casings are dictated by entry angle, ground conditions and size of the pipe rammer. Depending on the angle and ground conditions an auger boring machine can be used to clean out the casing, if not the HDD rig can clean out the casing with a forward reamer.
Developing its Process
Kamloops Augering & Boring Ltd. (KABL) completed its first surface casing in 1996 for the Olympic Pipeline under the Toutle River near Castle Rock, Washington. The oil pipeline was approximately 56 km away from Mt. St. Helens and years of volcanic run-off (including large rock) had threatened the integrity of the pipeline and prompted its replacement before the line could spill. The surface casing was installed at a 15-degree angle allowing the drill rig to start on-target and advance the drill bit down to the bedrock without any steering problems.
A decision was made to telescope the surface casing by installing 60 m of 750 mm and 150 m of 600 mm. The need to telescope arose from the requirement to remove the surface casing once the HDD crossing was complete. There were valid concerns that the casing could not be removed due to skin friction if it were not for the telescoping, which only left 90 m of the 600 mm casing surrounded by soil. As a result, the rig was setup 152 m from the riverbed, drilled to an approximate depth of 21 m below the river and followed a 1,400 m radius to the exit point on the side of a mountain. Once the crossing was complete, the surface casing was removed without incident.
Based on experience, innovation and the need for efficiency, KABL developed a portable structural ramp that can be mobilized to site to expedite the casing installation.
Traditionally, prior to arrival, a dirt ramp is constructed at the designed angle of the surface casing. The dirt either is brought in or is located within the construction site. Depending on the entry angle of the surface casing, the auger boring machines may not be able to clean out the casing, which means the directional drill needs to be moved into position and the dirt ramp removed. The construction of an earth ramp can take up to a day to complete.
Construction, demobilization and HDD casing clean out may be required several times during the installation of a surface casing.
KABL built its ramp out of steel tubing and steel plate that could be adjusted for various installation angles. The entire structure fits onto a standard trailer with no setup required once onsite. The use of the ramp has reduced installation times by several days saving the owner money and reducing a job’s environmental impact by not having to bring in dirt to construct an earth ramp.
The Next Evolution
The pneumatic air hammer still has its place on smaller surface casings, but the KABL Hydrohammer has removed the need for telescoping and has allowed for larger diameter installation at greater lengths. The Hydrohammer is an S-90 hydraulic piling hammer manufactured by IHC Hydrohammer. It is operated with KABL’s patent-pending Hydrohammer Harness with Hydraulic Crowd Support System.
KABL designed the harness to work with its American Auger 84-96 boring machine. Depending on entry angle and with a regular setup, the harness can be removed and the auger boring machine can be used to clean out the casing upon completion. The setup and installation rate of a surface casing has almost been cut in half as compared to traditional pneumatic installations.
The surface casings can be installed from 10 to 30 degrees and the casings may only require minimal clean-out for welding on the next joint of pipe during the installation procedures.
The Hydrohammer does not require periodic spoil removal to advance the casing due to the high-energy transfer. The system incorporates a hydraulically charged, fully enclosed driving device with a compressed nitrogen chamber that is fired internally. The main advantage is the energy is transferred directly into the casing by means of an ultra-high-energy, low-frequency impact with an immense high-velocity acceleration (up to 1,800 G’s), which causes the soil particles to be forcibly sheered.
There is a dramatic reduction of the carbon footprint as the amount of diesel fuel required to operate the Hydrohammer is significantly less than what is required for a pneumatic air-hammer installation.
Since, 1996 KABL has successfully completed hundreds of surface casings installations and extractions for numerous HDD contractors. The surface casing has become instrumental in the HDD industry and is designed into many crossings where unconsolidated formations are present on both entry and exit side. The result has been a more consistent pipeline installation with less environmental impact and reduced costs.
Harry Dickinson, Kamloops Augering & Boring Ltd.