Project contractors McConnell Dowell completed the drill using the intersect technique, which assists the construction of longer directional drills. The project used an American Augur DD625 rig, in conjunction with smaller Vermeer D80 and American Augur DD140 rigs supplied by subcontractor Strega.
The 280 tonne capacity DD625 rig was used to drill a pilot hole 30 m below the surface, for a distance of 1,817 m. This rig was equipped with the Paratrack 2 steering system which includes a magnetic field source located 8 m behind the cutting head and mud motor. The rig encountered soft soil at the far end of the drill, and steering beyond this point became difficult.
The smaller Vermeer D80 rig was set up at the planned exit point and used to steer a second 3.5 inch diameter drill string over 60 m to intersect with the cutting head of the main rig. A second Paratrack 2 system allowed the steering engineers to guide the drill string downhole until the two cutting heads touched.
The American Augers DD140 was then used to install a larger diameter drill string over the top of the 3.5 inch drill string, before installing a 14 inch diameter casing pipe to the intersect point.
Article continues below…The contractors are now drilling a parallel hole of a similar length for the installation of the 24 inch diameter gas pipeline.
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