HCLS: A Simple and Affordable Heave Compensated Landing System
Authors: Guinn Mitch 
Published: October 2008

In 1993, the Flowline Group of Shell Deepwater Services (SDS) developed and patented a Heave Compensated Landing System (HCLS) for use in placing fairly lightweight subsea pipeline repair equipment on the seafloor, utilizing the cranes on a pipeline lay barge.

In the continuing effort to reduce the costs of subsea installations, SDS and Shell Exploration and Production Company's (SEPCO) Drilling Group further developed this technology to enable extremely heavy and fairly sensitive subsea production equipment to be landed from a variety of vessels softly and accurately on the seabed in almost any water depth. As a result, subsea production equipment can now be installed from much smaller Anchor-handling Vessels (AHVs), instead of the more costly traditional construction vessels and drilling rigs.

The HCLS has been successfully used to install tubing head assemblies and subsea trees for the Na Kika project in water depths up to 7,300 fwd, as well as for several other projects in shallower depths. Cost savings over conventional installations utilizing a drilling rig or other heavy lift vessel have approached 50%. Opportunities for use of this technology to install other types of subsea equipment are quickly expanding, as there appears to be no weight or depth limit to using the HCLS method. This new development in subsea installation will enable profitable development of future subsea projects as the oil industry attempts to develop smaller fields and move into deeper water and more hostile frontier areas.

Introduction

Investigating the various installation methods that are suitable for use in water depths of greater than 5,000 feet began with the planning for the Nakika Project, a joint development between Shell International Exploration & Production Inc. (SIEP) and BP Exploration & Production Inc. (BP). The Na Kika Field is composed of five independent fields - Kepler (MC-383), Ariel (MC-429), Fourier (MC-522), Herschel (MC- 520), East Anstey (MC-608), which are being completed as subsea tiebacks to the centrally located Nakika host facility at MC-474. A sixth field, Coulomb (MC 657) will be tied back to Na Kika as production capacity becomes available. The seabed at these wells stretches across almost 40 nautical miles, from approximately 5,700 fwd to the deepest well located in approximately 7,600 fwd. The planned completion operations were performed by the Transocean Marianas drilling rig, a 5th generation MODU, which was anchored at each location using olyester ropes and suction piles.

In earlier subsea field developments, the two innovations of unloading the completed wells directly into the flowline and using a full bore isolation valve (FBIV) instead of a tubing hanger plug eliminated the need for using a completion riser.1 These step changes allowed the possibility of leaving the marine riser deployed, towing it between locations. At the deeper water depths of Na Kika, not having to retrieve the marine riser and re-run it for each well, would save an estimated minimum of 4-6 days of rig time per well, provided that a method of installing the tubing head spool (THS) and the subsea tree could be developed that did not require the use of the main derrick of the MODU.