Drilling Out into the Ocean – Lessons Learned from a Pilot Bore Geotechnical Exploration

摘要

Nalcor Energy is developing the Lower Churchill Project, involving hydroelectric generation and transmission fromrnLabrador to the island of Newfoundland. As part of this work, horizontal directional drilling (HDD) method will bernused to construct six (6) landfall crossings beneath the shorelines of the Strait of Belle Isle (SOBI) separatingrnLabrador and Newfoundland. Each HDD installation will consist of a 10.75-inch (273 mm) diameter steel casing tornhouse individual HVdc electrical cables (to be installed later in a second pass). The length of the steel casingrninstallations will range between 4,921 feet (1,500 metres) and 8,200 feet (2,500 metres). The termination depth ofrnthe HDD installations will range between 200 (60 metres) and 295 feet (90 metres) below sea level. The geologyrnconsists of ocean floor sediments, sedimentary sandstone, limestone, dolostone, shale and Precambrian granite. Thernocean floor sediments consist of clay, silt, sand, gravels, cobbles and boulders.rnAs part of an in-depth risk reduction measure, a HDD pilot bore geotechnical investigation was completed tornsupplement traditional shoreline-based geotechnical investigations. This pilot bore program also provided a meansrnto assess the applicability of using standard and non-standard guidance systems and drilling approaches from bothrnthe HDD industry as well as the oil and gas industry. In addition, it provided a means to verify contingency plansrndeveloped for the proposed HDD installations. This paper highlights the lessons learned from the 2011/2012 HDDrnpilot bore field program used to develop the ultimate SOBI landfall HDD design crossings.