Making riser handling faster and safer

When conventional, manually operated riser-handling tools appeared incapable of fully supporting a particular drilling riser system that one of our clients was installing, it was time for Claxton to go back to the drawing board. In response, we initiated an intense in-house development program to create an innovative hydraulic tool. The new tool can drastically cut rig time – and costs. It eliminates the need for scaffolding and manual handling, and also offers protection to the very expensive associated riser connector.

The limitations of the conventional heavy-duty segmented handling tool became apparent on this project when it could not hold the required internal pressure when attaching to the 18¾”, 15-M NT-2 tension joint. After exhausting all the options, including changing the construction material and altering the segment design, our team concluded that the client’s requirements could not be met with that design. We needed to take a new approach.

The riser handling tool saves copious amounts of rig time.

Our engineers set about re-engineering the conventional riser-handling tool. In 10 months, they had designed, manufactured and tested a new multipurpose, hydraulically actuated running tool. This involved internal design review, client design review, third party approval and the manufacturing and mechanical completion activites were conducted in accordance with Norsok standards.

This not only met our client’s needs, it also overcame the shortcomings of the manually operated variant. For instance, the conventional tool requires scaffolding to be erected in order to reach the NT-2 joint. This adds time to the operation and introduces safety risks from the potential for dropped objects. The tool’s operation is time consuming because each of the 12 segments has to be manually secured onto the tool’s housing using a threaded stud and nut, which are tightened using a standard torque package.

Incorporating hydraulics to riser handling
In contrast, our new tool’s hydraulic operation means riser handling can be much quicker: scaffolding does not need to be erected and the tool hydraulically locks itself on to the NT-2 joint in seconds. Crucially, because it is hydraulically actuated, the new tool can be operated remotely by means of a dedicated combined hydraulic power unit and reel, which reduces the risk of harm to personnel.

During the tool’s first real-world application, our client, a Norwegian drilling operator, used it to run and remotely pressure test three 6,019-psi (415bar) full-riser systems. The tool cut 4.5 hours of rig time from each run, decreased the project costs by $2.9 million and reduced the risks to safety.

We will now be offering the tool to all clients as part of our strategy of continuing improvements in efficiency and safety. The tool’s key features include its ability to perform a wellbore pressure test to 7,000 psi while holding the tension at 308 te (flanged and quick-connect systems are available to 12,200 psi) act as a contingency method for applying 400 te of tension to the drilling riser system before blowout preventer installation (with no internal bore pressure) interface with either a Grayloc 192 or 196 gasket seal profiled, 18¾”, 15-M NT-2 pin by means of a removable adaptor housing the seal elements lift a drilling riser tension joint weighing up to 20 te and measuring up to 12 m. In addition, its vital safety features include visual indicator rods that show whether the tool is locked or unlocked, and a manual override feature to lock and unlock it.

The Claxton tool is 3.52 m long, has a maximum outside diameter of 1.16 m (45.¾”) it is wise to mention this in imperial as it connects with the rotary table) and weighs 5.1 te. It is DNV approved and is verified in accordance with DNV-OS-E101 and API 16F, 6A, 8C and 7G. It is supplied as a complete package with a DNV-2.7-1-certified container for transportation and storage, and a combined ATEX-approved hydraulic power unit and umbilical reel to power all functions.

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Riser handling tool in the field.

Operational advantages
An important feature of the tool is that it offers protection for the NT-2 riser connector. This expensive piece of hardware is at risk of being damaged by the riser when it is moved by the crane. The key element of an NT-2 connection is the seal profile located at the top. When our new tool is installed on the NT-2 joint, this seal region cannot be accessed because the tool envelops it and prevents damage through mishandling or from dropped objects.

The new tool also helps to safeguard against weather window issues, as it can apply tension if sea conditions worsen during the installation process. In this situation, a manual tool could not operate to 400 te without a specially designed tool mandrel and, crucially, could not maintain tension while being highly pressurized. This is not an issue with the new tool because it has been specifically designed to meet these parameters.

We have also eliminated some of the operational use restrictions. For instance, the manual version requires over-the-side scaffolding work, which cannot be undertaken at night on some Rigs. The hydraulic riser-handling tool has no such operational restrictions and therefore does not impact on our clients’ decisions regarding when to run or pull the riser system during a drilling campaign.

Slimline tension rings

Claxton pioneered the positive grip tension ring
The primary benefit of a slimline tension ring is not realized during running operations but in pulling operations.

The benefit of the slimline tension ring comes into effect when you are drilling more than one slot at a given time and you need to “hop” the riser from one slot to the next. This means that at some point you will pull the tension joint through the rotary table. By design, the slimline tension ring does not need to be removed to allow the tension joint to pass through the rotary and thus saves rig time. The tension joint can then of course be re-run through the rotary table making further time savings.

Further benefits can be realized from testing the joint using a previously installed Claxton slimline tension ring, which reduces the Texas deck exposure. Space and lifting constraints mean it can be time consuming to get a traditional tension ring onto the Texas deck for installation on an in situ riser. We recognised that if we could design around these issues and still maintain performance, our clients would save significant amounts of time.

A Claxton slimline tension ring can be taken from a half-height container directly onto the drill floor and attached to the riser. Then the riser and tension ring are run through the rotary table, which cuts the rig time required and so reduces costs for our clients.

Key takeaways
The new Claxton hydraulic riser-handling tool provides a means to fully support a drilling riser system during installation and recovery operations. It offers time and cost savings, and a range of safety and operational benefits, including remote circulation and full pressure testing of the drilling riser, no scaffolding requirements and protection of the associated riser connector.

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