DRILLED SHORE APPROACH SETS RECORD ON CANADIAN PIPELINE
Installation of the Anderson Bay crossing of the Vancouver Island pipeline (OGJ, May 6, p. 76) involved the world's deepest directionally drilled pipeline shore approach, according to the contractor, VSRB Horizontal Drilling Co.
VSRB is a Royal Volker Stevin company based in Papendrecht, The Netherlands.
The work involved drilling holes for two 41 0-mm (16 in.) casing pipelines from a clifftop spud-in position to a point on the channel floor 390 m (1,279 ft) offshore and in water 220 m (722 ft) deep.
The drilled profile was some 670 m (2,198 ft) long and passed through rock strata.
The gas carrier pipelines could then be installed later by being pulled from offshore through the drilled holes.
LONG-AWAITED PROJECT
The Vancouver Island natural-gas pipeline is a $300 million (Canadian) project by Pacific Coast Energy Corp., Vancouver, to move natural gas to Vancouver Island on Canada's west coast.
The project, which was under consideration for almost a quarter of a century, entailed the installation of approximately 500 km (310 miles) of land line and 50 km (31 miles) of twinned subsea line through some of Canada's protected wilderness and environmentally sensitive areas.
An intermediate island along the pipeline route, Texada Island, presented an opportunity to adapt directional drilling to the pipeline shore-approach, says VSRB.
The coastline along this portion of the route is very steep bedrock with an average inclination of 43. It is characterized by numerous ledges and near-vertical faces to a water depth of 220 m.
An engineering assessment of the geological conditions and sensitive marine environment at this location showed that the planned dual 273 mm (10 in.) steel pipeline shore approach was suitable for a directionally drilled installation, according to VSRB.
The shoreline and seabed profile, along with the difficult ground conditions, ruled out the alternative trenching and blasting method.
Directional drilling, the solution chosen by Pacific Coast Energy Corp., offered deep cover depth security, rapid installation, and minimal disturbance to the sensitive shoreline environment.
In early 1990, VSRB contracted to install the shore approach.
DRILL SITE, DEVIATION
The on-shore drilling spud-in point was located on a plateau approximately 200 m from the shoreline and 50 m above sea level (Fig. 1). This location provided sufficient room for the drilling rig and its associated equipment.
The designed drilling profile had an entry angle of 45, with this angle being deviated along the 670-m length of the hole to exit at close to 80 from vertical.
The build rate of the profile was limited to 2.4/30 m to allow ease of installation of the natural-gas pipeline. The design exit point was in a nearly vertical rock face with a gently sloping seabed below, which made it an excellent location, according to VSRB.
Because it was imperative to exit in this rock face, Pacific Coast Energy established tolerance parameters of 1 m in the vertical plane and 5 m in the horizontal plane of the targeted exit coordinates.
The diameters of the drilled profiles were 550 mm (21.7 in.). Both were drilled 20 m apart and lined with 410 mm (16 in.) steel casing cemented in place to facilitate the installation and corrosion protection of the 273 mm (10 in.) natural-gas pipelines.
VSRB says it decided first to drill a 251 mm (9 in.) pilot hole along the designed profile. After pilot-hole completion, the profile was opened in two passes to the 550 mm design diameter (Fig. 2).
The first pass opened the hole to 380 mm (15 in.); the second opened the borehole to its required 550 mm diameter.
The rig used by VSRB to drill the two holes was a highly automated, slant oil field-type rig (Fig. 3). The rig featured a 450-kw electric top-drive capable of generating 24,000 Newton-m (17,700 lb-ft) of torque and 25,000 daN (56,200 lb) pull down capacity.
The computer-controlled hydraulic system provided precision drilling and an automatic pipe-handling system.
ON TARGET
In late June 1990, VSRB mobilized equipment and supplies to the drill rig site on Texada Island. The two profiles were drilled in slightly more than 50 days. The drilling was accurate enough that the exit points were exactly on target.
Next, the steel casings were cemented into position by a method devised by VSRB. This used the available hydrostatic head as a balance to a calculated cement volume pumped down the casing annulus.
The cement plug was then set in place at the exit point, and the remaining annulus length was grout filled back to the spud point.
The final step was to install a draw wire along each casing ready for the later gas pipelines' pull-in operation.
The drilled shore approaches were completed by Sept. 7, 1990, 61 days after drilling had begun.
Approximately 1 month later, the 273 mm marine pipelines were pulled from offshore to shore through the drilled holes and are now permanently positioned in their casings ready for gas flow later this year.
Copyright 1991 Oil & Gas Journal. All Rights Reserved.