When the issue of subsea wells is broached all too often the top-hole construction is a neglected area. But if Norwegian-based Neodrill get its way that will soon change.

Neodrill’s Conductor Anchor Node (CAN) system uses high load carrying capacity suction anchors to secure seafloor mooring points via a large diameter, relatively short cylinder. Unlike traditional methods, no cement is required, negating the risk of conductor problems due to cementing failure. It also provides a well foundation to be drilled or jetted through, or with a preinstalled short conductor. It already has been proven in 17 installations to date with 14 runs in Norway and one on the U.K. Continental Shelf (UKCS).

However, outside Norway there appears to be a reluctance to adopt what appears to be a valuable tool to reduce costs and speed time to first oil. The technology is at the heart of a new joint industry project (JIP) by the Industry Technology Facilitator (ITF) in collaboration with Maersk Oil, Nexen, Shell, Siccar Point Energy, TechnipFMC and the Oil and Gas Technology Centre. The role of the JIP is to investigate an alternative well foundation technology for subsea E&P wells. The aim is to examine the versatility and robustness of CAN technology as an alternative well foundation for most seabed soils.

Breaking From Tradition

The traditional approach in the U.K. sector is to drill a 36-in. to 42-in. hole, down to about 92 m to 107 m (300 ft to 350 ft), then run a CAN-ductor string into that, and then cement that string. The process requires large equipment, rigs and several days of rig time to get this first operation underway. “It’s a really crucial operation, especially if the well’s going to be a producer,” said Ben Foreman, technology manager for ITF. “You need to get that CAN-ductor in vertically, and you need a good cement job to ensure that you’ve got sufficient load-bearing capacity for your well architecture. Every operation you do afterward is dependent on having a good CAN-ductor cemented in place.”

The verticality is important and must be within 1 to 1.5 degrees, facilitating easy landing of the BOP and christmas trees on top without issues such as latching and unlatching. The other big challenge is the cement itself, especially in most areas in the North Sea where seabed conditions are soft.

Saving Cost, Time

The first major benefit of the new CAN technology is that a rig is not required for installation, simply a suitable supplier intervention vessel with a crane.

“You just lift it and you drop it onto the seabed. The first penetration is just through the weight of the CAN-ductor itself,” Foreman explained. “The CAN-ductor is like an upturned bucket, and it’s very similar to what has been used in this industry for years to anchor FPSO [units]. After the initial penetration there’s a suction cap on the top, and an ROV sets a pump onto the top and starts to pump the seawater out of the CAN-ductor. This pressure difference sucks it down farther into the seabed. There is no drilling required beforehand.”

Foreman estimated that because this is carried out offline with an intervention vessel or a larger supply vessel without a drilling rig there, it is only the tenth of the traditional cost.

“The other really nice thing about the technology is these CAN-ductors are reusable,” he added. “That’s a big potential cost saving there, because typically when we cut and abandon wells, we don’t reuse the CAN-ductor or the well housing—well not without a serious, serious refurbishment anyway.”

Addressing Industry Concerns

The sector traditionally constructs wells the same way it has since the 1920s. Although the CAN technology has been utilized a lot in the clay soils on the Norwegian Continental Shelf it has yet to be tested on the sandy soil on the UKCS seabed and locations that contain a mixture of soils. Foreman believes companies involved in the JIP would have separately investigated the technology with their own research and simulations.

“With a joint industry project and everyone pulling together data, they can all learn from each other,” he said.

Another area of concern that is holding back adoption of the technology is drilling the next smaller hole size from below the CAN-ductor. “A typical conductor string is about 80 m [262 ft] long, whereas a CAN-ductor is much shorter at 10 m to 15 m [33 ft to 49 ft] long,” Foreman said. “There’s a lot of unconsolidated soil that typically we would have cased off and cemented off. There is some concern that, when using a CAN-ductor, when you drill out from underneath it, whether the soil there is just going to wash out and cause stability issues. The other half of this JIP is technical experts looking at the geotechnical and geomechanical data to give guidance on drilling procedures and giving operators confidence that, when they drill the next section, they’re going to maintain well integrity.”

For Neodrill, the JIP is a milestone in bringing CAN technology to a wider user group within the UKCS.

“Building on the knowledge we have obtained from previous runs, we can assess its suitability for other substances including sand,” added Neodrill CEO Jostein Aleksandersen. “Compared to the conventional conductor, we already know that CAN demonstrates many advantages, including the ability to save rigs time and well costs as a smaller and more cost-efficient vessel is used for CAN/conductor installation ahead of the drilling unit arrival.

“The JIP aims to demonstrate further cost efficiencies as well as robust and versatile solutions for subsea exploration and production wells,” Aleksandersen added.

—Mark Venables

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