Claxton subsea drilling template instrumental to Tombua-Landana

Subsea Drilling Template for Tombua Landana
The first of two Claxton contributions to the giant Tombua-Landana project is not that easy to spot, even though it is literally fundamental to this world-class project.

Production facilities weighing 36,500 tonnes are supported on a compliant tower weighing 56,400 tonnes. This stands on a tower-base template of 3,000 tonnes, which in turn rests on a levelling-pile template – under which, right on the seabed, there is a 12 slot subsea drilling template providing 9 well slots and 3 docking slots, designed, supplied and installed by Claxton.

Weighing just 30 tonnes, the small but perfectly-formed template provides the pattern for the first wells drilled before the giant platform was installed. Indeed, it also determines the location of the platform and all 38 wells that will be needed to complete the development in the years to come.

Claxton won the job of providing the template for CABGOC on the back of lessons learned during the installation of a similar template for the Benguela-Belize platform. On that occasion the company was called in late in the day to help install the template, which had been provided by another supplier. “We got the chance to demonstrate our expertise in this area on Benguela-Belize and, as a consequence, were awarded the contract both to supply and install the pre-drilling template on this project,” explains Rowan Patterson, Claxton’s business development director.

The template was installed in two stages. It was initially lowered onto the seabed from an anchor-handling vessel. The Pride Venezuela semisubmersible drilling rig then picked up the template on drillpipe fitted with a Claxton-supplied overshot double-J running tool and carefully located it over a single well already drilled in the seabed. It was then correctly oriented, landed and locked onto the well’s 30-in wellhead housing. A further slot was then drilled through the template and a second 30-in conductor installed, at which point the orientation of the template was effectively fixed.

In all, four wells were pre-drilled through the Claxton template (of nine possible), each furnished with a 30-in low-pressure subsea wellhead and an 18¾-in high-pressure wellhead on 20-in casing. A docking pile was also installed through an outer, purpose-designed slot on the template before drilling was suspended and the rig moved away.

Subsea Drilling Template being installed
The Tombua-Landana template being installed…

This also marked a pause in Claxton’s involvement, during which some serious construction work was undertaken. First, a levelling-pile template was fitted over the well template, followed by four levelling piles, their correct alignment being assured using two guide pin slots in the Claxton template. The main tower-base template was then added and 12 foundation piles installed; thereafter there was just the small issue of adding the tower itself and then the topsides.

At this point Claxton returned to carry out another pivotal task in the development: the tying back to the platform of two of the first four wells. (CABGOC took the decision to delay tying back the other two wells in favour of drilling further platform wells.) Claxton prepared all the procedures for a process that began with the removal of corrosion caps from the 18¾-in high-pressure wellheads and the landing of 26-in conductors on both wells to provide conduits back to the platform’s well deck. “The challenge here was to ensure the correct space-out of the 14 conductor centralisers spread along the nearly 40 conductor pipe joints,” says Patterson. “Accurate measurement and careful calculations ensured that with the conductors locked onto their subsea wellheads all the centralisers engaged perfectly within the guides situated between the bottom of the tower and the platform.”

For each of the wells, following the installation of the conductor, 13.3/8-in and 10.3/4-in casings were landed and locked into the subsea wellhead and a high-pressure wellhead fitted to the former at the platform welldeck ready to accommodate the production tree.

“There is great satisfaction from being involved in complex projects like this one,” says Patterson, “when everyone is required to play their part to the very best of their ability to ensure the overall success of the venture.” In this case, Claxton’s contributions were both essential to the timely completion of the project, both firmly on the critical path to first oil from Tombua-Landana.

Subsea Drilling Templates from Claxton…

Over 55 major developments have benefited from Claxton’s subsea drilling templates. Claxton can design, rapidly manufacture and fully install templates that help to assure correct well / conductor alignment. Our team has experience of developing installation methodologies for challenging situations. Meanwhile our template design library has options for all soil types and multiple different slot arrangements and configurations – these designs can be modified with both speed and relative ease to suit numerous applications.

Learn more about our Subsea Drilling Template capability…

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