Ensuring subsea asset integrity with protective structures from Claxton

You would be forgiven for thinking that there’s not much to get excited about when it comes to protective structures – they are, essentially, a cage placed on the seabed to prevent damage to equipment from fishing activity or dropped debris. However, as Claxton has recently proved on a project for Senergy, with the right mix of experience and equipment it’s possible to add real value to both the structure and the installation process.

Claxton was contracted by Senergy to utilize a structure which had been designed and fabricated for a previous project. Claxton was able to rapidly modify the structure for Senergy – and provide all the appropriate running tools which enabled a smooth installation.

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The subsea protective structure being prepared and installed

The structure, weighing some 5,570kg with a footprint of 3.8 square meters and standing 3.1 meters tall, was originally built to protect a Vetco SG1 Wellhead on the Dana Scolty field. After modification, the structure would again be used for Dana, but this time on a Dril-Quip SCS Wellhead – on Platypus well 48/1a-5, in some 142ft of water.

To accommodate the new Wellhead, Claxton fully refurbished the structure and lowered the landing ring. The spec also called for chemical inhibitor sticks to be fitted inside the structure – these sit just inside the wellhead profile and release chemicals which create a protective environment inside the wellhead, reducing corrosion.

Additionally Claxton fitted an array of our proprietary cameras to the structure – MULTICAM™ was specifically designed to monitor installation processes and MULTICAM™ units were mounted to observe the wellhead guide-cone at the base of the structure. An additional camera was mounted to provide a view of the engagement and disengagement of the J-Slot running tool.

The structure was fitted with extension legs which would be activated by a ‘sling sub’ arrangement. The sling sub would be operated when the structure’s running tool was disengaged – allowing the extension legs to drop onto the seabed and remove the potential for fishing nets to be caught on the corners of the structure.

The protective structure was installed from the Transocean Labrador. The total operation from rig-up to the installing of the structure and rigging down was completed in just seven hours. It was here too that a Claxton tool was able to add significantly to the procedure. Claxton’s Jet Sub was installed on the running equipment which allowed for adjustments to be made during installation using a high pressure water jet to either offset currents or guide structures into position.

Neil Youngs, project engineer for Claxton, felt the Jet Sub was instrumental to the smooth installation of the structure:

We used the Jet Sub to guide the structure between 1.5 and 2 meters. We were working during a strong spring tide and without the Jet Sub we would have taken considerably longer to engage the structure over the wellhead.

Neil continues, “We’ve worked with both Senergy and Dana on previous projects – they’ve been great partners to work with. So we were especially pleased to have worked with them again on this operation and to deliver the structure, modifications and installation in such a timely manner”.

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