Less is more

Unmanned facilities are being given serious consideration offshore Norway. Elaine Maslin reports.

Percentage of unmanned platforms per North Sea sector. Unmanned distribution. Image from Ramboll.

For some regions, unmanned facilities are the norm. The southern North Sea – off Denmark, the Netherlands and the UK – is strewn with them, for example.

Yet, in the same basin, they’re a little bit anathema. For Norwegian operators, the choice seems to be one between a manned facility and a subsea development. Until now. Last year, faced with wallet busting subsea development costs, Statoil opted for a remote controlled unmanned wellhead platform for the Vestflanken 2 project at Oseberg.

Earlier this year, the Norwegian Petroleum Directorate (NPD), which has welcomed Statoil’s move at Vestflanken 2, commissioned a report from engineering house Ramboll on unmanned facilities. The report says that unmanned platforms can be cost- and production-efficient development concepts in shallow water on the Norwegian shelf.

For the NPD, unmanned facilities could be a solution for shallow water marginal fields. Here, a minimal-facility would act as a satellite platform tied back to a host installation, with power, chemicals, utilities, signals and controls typically supplied by the host via an umbilical. The benefits, it says, are reducing initial capex, in terms of facilities cost, but also installation costs and opex.

Minimal facilities scopes. Image from Ramboll.

Track record

In the North Sea, there are already more than 200 unmanned wellhead platforms, dating back to the 1980s, according to Ramboll, which has designed many unmanned and minimal facilities platforms for the southern North Sea as well as the Gulf of Mexico and Middle East. Some 148 of the 200 are in the UK sector (which has 590 platforms in total), mostly in the southern North Sea gas basin in 20-150m water depth. Some 14 are offshore Denmark and 47 are in the Dutch sector, in 20-70m water depth.

The attraction in those areas is water depth and availability of other facilities to tie into. Unmanned facilities are at home in 35-150m depth, Ramboll says, and have helped to tap smaller fields where lower capex has been key. There are 200 in the Middle East, and around 1000, or 25%, in the US Gulf of Mexico, according to Ramboll’s report for the NPD.

Norway has five normally unmanned facilities, in 70-125m water depth: Tambar and Hod (operated by BP), Embla (ConocoPhillips), Sleipner B (Statoil) and Huldra (Statoil), which was shut-in in 2014, according to Statoil.

While in other areas, shallow water, small reservoirs and proximity to infrastructure have helped drive use of normally unmanned facilities, the norm in Norway has been for bigger fields, driving up the scale of its facilities, says Henrik Juhl, Ramboll’s senior director, offshore pipelines, subsea and jackets. “Going small hasn’t been part of the mindset,” he says. There also hasn’t been the same proximity to infrastructure and shallow water depths as in other areas, and regulatory requirements have been limiting, says the Ramboll report.

Yet, there appears to be potential. According to the NPD there are approximately 90 discoveries on the Norwegian Continental Shelf (NCS) under consideration for development. The lion’s share is marginal in volume, and many of them are candidates as tiebacks to nearby host platforms. But, many are located less than 50km from existing infrastructure, and many even less than 20km, a range which an unmanned wellhead platform could become a very efficient solution, Juhl says.

There are various options for minimal facilities, Juhl says, with the smallest being a monopile, or a “wellhead on a stick,” as it’s been called. It has been used in the Gulf of Mexico, Middle East, Denmark [Tyra South East A and Cecilie] and the Netherlands. These often just operate one well.

Mono column designs

Indeed, mono-column platforms (MCPs) are a viable option for the Norwegian market, according to Bergen Group and Singapore-based Calm Oceans, which agreed to an agency deal to market the concept earlier this year. Their concept is a self-elevating, multipurpose jackup with up to 5000-tonne deck load, for up to 130m water depth.

The platform essentially comprises a deck box, four-chord square truss structure (mono-column) and a mat foundation. With the mat design, the MCP can operate in oil fields with soft seabed, seen as challenging for conventional jackups.

The MCP design, which comes from Brian Chang, who owns Calm Oceans and 33.1% in Bergen Group, has been classed by ABS, adhering to mobile offshore unit code 2008 and other relevant IMO guidelines.

The advent of access solutions such as walk-to-work systems could be seen to be an enabler for this technology, because it means helicopter decks are not required, which come with all manner of support systems, from lighting to deluge systems and power systems to support those, increasing facility size, Juhl says. Indeed, Statoil is planning to use gangway access systems off support vessels for when staff are needed on the Vestflanken 2 facility.

Just how welcome using motion compensated gangways will be offshore Norway is yet to be seen. Such technology has been used in the North Sea for a number of years, both in response to helicopter groundings in 2013-14, giving an alternative means to get staff to work in the UK sector, and also as a regular access option for offshore wind farms from smaller vessels. To economically make use of such a system, ideally you would need 2-3 normally unmanned or minimal facilities operating that could be served by one vessel.

Regulations

There are also regulations with which to contend. “In Norway there are challenges in terms of regulations and meeting all the guidelines in place,” Juhl says. “In other areas regulations are driven more by a safety case [which enables more freedom in the design].” In Norway, regulations and guidelines were drawn up for an industry that had been focused on very large facilities, so it is felt they don’t address unmanned facilities.

Ramboll’s report says that regulations do support the concept of unmanned wellhead platforms. But, it says the industry’s “underlying guidelines and NORSOK standards have more focus on mitigation measures requiring more systems, equipment and maintenance, and therefore do not support the concept of unmanned wellhead platforms, and most unmanned wellhead platform concepts will be non-compliant with the guidelines and the NORSOK standards. But in principle, the underlying guidelines and NORSOK standards are only one way of fulfilling regulations. Alternative solutions may be chosen, provided that the operator can demonstrate that these are safe and fulfil the detailed requirements in the regulations.”

However, the report suggests a new guideline and/or a NORSOK standard should be developed that provides an approach for the design of unmanned platforms on the NCS.

There is interest in this concept, not just from Statoil. So far, Ramboll has done 5-10 studies for minimal facilities in Norway, including Statoil’s Vestflanken 2, but also for projects for ConocoPhillips and Total.

For Total, Ramboll made a study for an alternative for the Tor field, where the facilities were shut in on 1 January this year, having reached the end of their life. Yet, it is thought that there are still reserves that could be extracted if an economic option could be found. Ramboll also did studies for unmanned and not normally manned satellites for the Johan Sverdrup field.

Vestflanken 2

Vestflanken 2, artists’ impression. Image from Statoil.

Statoil and partners Petoro, Total and ConocoPhillips have estimated the development cost for Vestflanken 2 as NOK 8.2 billion (US$960 million). This investment will enable the production of around 110 MMboe.

The wellhead facility will have 10 well slots. To increase the recovery of oil, two of the slots will be used to inject gas. In addition, two production wells will be drilled from an existing subsea template on the Vestflanken.

Further injection will take place by bringing in gas through a new pipeline from the gas injection system which already exists in this area. The wells on Vestflanken 2 will be controlled from the Oseberg field center, where the oil and gas will also be processed.

The wells at Oseberg Vestflanken 2 will be drilled by the new category J jackup drilling rig Askepott, which is currently under construction. It is owned by the Oseberg license.

Contractors selected for work bringing on Vestflanken 2 include Technip (pipelaying), Ocean Installer (marine construction), Heerema Fabrication Group (EPC of the unmanned wellhead facility), and Heerema Marine Contractors (transport and installation). In addition, Aibel will work on the Oseberg field center to receive the well stream from Vestflanken 2, and FMC Technologies will supply two subsea trees. •