Design And Installation Of An Offshore Flowline For The Canadian Arctic Islands
Authors: Palmer A.C. , Baudais D.J. , Masterson D.M. 
Published: October 2008

In April 1978, the world's first Arctic subsea production gas well was connected to production facilities onshore, through a 1200m flowline bundle connected to the wellhead by a diverless subsea flowline connector. This paper describes the design, installation and connection of the flowline bundle, and the shore crossing protection system.

INTRODUCTION

On April 23, 1978 Panarctic Oils Ltd. completed its Drake F-76 gas well off the Sabine Peninsula of Melville Island in the High Arctic. Six days later gas flowed to shore by a marine flowline and a test program was started to evaluate the performance of the well-flowline combination. This was the culmination of a two year engineering and construction program to demonstrate the feasibility of drilling such a well offshore in the Arctic, of completing it with a subsea wellhead and of connecting it to a marine flowline to onshore process facilities.

The work was funded jointly by Panarctic Oils Ltd., Petro Canada and Alberta Gas Trunk Line Co. Ltd., as a major step in establishing the technology for exploiting Arctic gas reserves. Most of the gas found in the Arctic islands Sverdrup Basin is offshore, and its development will require extensive gathering systems, with wells up to 20 km offshore in water up to 400 m deep. Ice forces make the use of conventional fixed platforms impractical.

This paper is concerned with the design and construction of the flowline. The well itself is described in another OTC paper. It is not possible to examine here all the aspects of this complex project, and therefore the paper centers attention on its unusual features.

PROJECT LOCATION

The well is in the Drake gas field, on the east side of the Sabine Peninsula. The geology permitted the well location to be chosen to meet the following requirements:A minimum length of flowline.A well location deep enough for the top of the wellhead to be just below 45 m depth, the keel depth of the largest of the ice islands that occasionally drift through Byam Martin Channel.A relatively steep shore crossing, so as to minimise the cost and difficulty of protecting the flowline from sea ice.A suitable onshore area for pipe make-up.A reasonably level area of seabed on the shore side of the wellhead, suitable for the planned connection method.

The well location, 1200 m offshore, and flowline route shown in Fig. 1 were chosen after a reconnaissance survey in January 1977. A detailed marine survey followed: it included bathymetry, side-scan sonar and bottom profiling, current metering, sea-bed coring, ice thickness measurements, and temperature profiling to locate sub-bottom permafrost. The site investigation has been described elsewhere in more detail.

SCHEDULE

A study in the fall of 1976 confirmed that construction of the flowlines was technically feasible, and that it could be completed in the early months of 1978. Sea ice was a severe constraint on the schedule. In September the sea freezes, and the ice thickness grows rapidly, so that it can support light equipment by November and heavy construction equipment in the first five months of the year.