PILED TOOL WILL LEVEL SUBSEA WELL TEMPLATE FOR HEIDRUN TLP

Piled leveling tools were recently contracted for use during the installation of the subsea well template for Conoco Norway Inc.'s Heidrun tension leg platform (TLP) in the Norwegian sector of the North Sea. The $1 million contract was issued following completion of a 7-month, joint-industry study that successfully tested a prototype 500-ton, Latch-Lok tool (see picture), Two 900-ton hydraulic jacking capacity tools will be used on the Heidrun TLP.

Jan. 13, 1992

3 min read

The $1 million contract was issued following completion of a 7-month, joint-industry study that successfully tested a prototype 500-ton, Latch-Lok tool (see picture), Two 900-ton hydraulic jacking capacity tools will be used on the Heidrun TLP.

Marine Contractor Services, Houston, will build the two tools to accommodate 72-in. pilings. The tools will be used to level a seafloor well template at a depth of approximately 1,130 ft. The work is scheduled for around August 1992.

The leveling tools are employed after a template has been positioned on the seafloor and anchor pilings have been driven through the template sleeves. One or more tools are lowered and landed on anchor pilings at the low side of the template. No diver support or guidelines are required.

Latching arms are then hydraulically extended downward until latches engage a prepared groove on the template sleeve (see figure). As the latching arms are retracted, the template is lifted to level.

Temporary holding devices are then actuated to hold the template until the template can be permanently secured with cold-forged connections or, more rarely by conventional grouting.

After leveling, the tools are retrieved to surface.

Template leveling systems can be divided into basically two categories: mudmat based and pile based.

Mudmat-based systems have floating or articulated mudmats with hydraulic jacks connecting the mudmat to the template structure. The jacks and hydraulic system are integral to the template. During leveling, the mudmats react against the soil to raise the low corners of the template.

The advantage of mudmat-based systems is in allowing the template to be leveled prior to commencing piling operations.

Several disadvantages are that mudmat systems are comparably more expensive than pile-based systems due to the increased number of jacks, complexity of the hydraulic system, and a more complex mudmat structure. The leveling system must also be sacrificed after use or installation vessel time must be spent removing salvageable components.

Should the system fall or become damaged there is no simple or inexpensive way to change-out components. Also, the soil provides for an unreliable foundation to react against.

On the other hand, pile-based systems use the driven pile to react against while raising the low corners of the template. After the piles have been driven to grade, the leveling tool is deployed from the construction vessel and stabbed onto a pile at the template's low corner. The leveling tool then connects itself to the template sleeve and can then raise the corner of the template while reacting against the pile. Two or more tools can be used simultaneously.

The disadvantage of this system is that leveling must take place after the piles have been driven to grade. This is not viewed as a prohibitive problem because studies and offshore experience show that a structure can be leveled to up to 3 after all piles have been driven, and during installation the maximum out-of-level condition for most structures will be less than 3.

Advantages for pile-based systems include that for equal jacking capacity to mudmat systems, the outlay for hydraulic cylinders and associated components is considerably less. The equipment is retrievable and can be reused. This allows the possibility of using the pile-based system on a lease basis. If problems arise, the pile-based system can be retrieved and repaired or backup equipment deployed.