Well intervention units in a class of their own

Alexander Wardwell
Thursday, May 20, 2010

Rapid technological and market developments in the offshore industry over the past five years have put pressure on class to develop rules and notations for a new generation of specialised well-intervention offshore vessels. DNV's Alexander Wardwell reports.

Driven by burgeoning global demand for energy, subsea exploration and well construction has experienced a boom in the past decade. According to consultants Infield Systems and Douglas Westwood, the total number of subsea wells will climb to more than 5500 by the end of 2010. While some projects may be delayed due to financing issues related to the global economic downturn, the rapid construction of new wells is likely to continue, if not accelerate, in the years to come.

This remarkable growth has created challenges for energy companies and suppliers alike. Increased demand for fuel has forced many energy companies to re-evaluate stranded or marginal fields, work in deeper waters, employ more complex tieback solutions and improve recovery rates for ageing wells.

These emerging demands have pushed operators of well intervention units to develop new technologies to improve access to subsea wells, creating a demand for more efficient subsea well intervention systems, including riserless light well intervention (RLWI) units. While not appropriate for deep water, RLWI units are optimal for repair, scale removal, installation and manipulation of some equipment (such as valves, plugs and screens), re-perforations, zone isolation, fluid sampling, PLT, chemical treatment and well abandonment, among other services.

In the past, this work was performed by giant semisubmersible drilling rigs. However, developments in dynamic positioning systems, ROVs and other specialised onboard systems have allowed well intervention equipment to be placed on monohull units, which can move quickly from one well to the next, helping to reduce chartering costs and improve well recovery rates. Riser well intervention units are still preferred for some kinds of work and in water depths greater than 500m, but new composites now being developed for wire lines may soon allow RLWI units to work in deeper waters.

Gender issues
The first monohull well intervention unit (Seawell, now operated by Well Ops) was built in 1986 by Stena Offshore and entered service the following year equipped with a 12m long, 13t subsea wireline lubricator built by Camco (OE March 1987). The concept proved a success, and over the next ten years, demand for LWI units grew. However, because these units are often similar in design to offshore supply, support or multipurpose vessels, there was uncertainty on how to class them: are they vessels or mobile offshore units?

With its extensive experience in the North Sea (home to some 40% of the world's subsea wells) and other regions, DNV recognised the need to manage these issues and launched a development project in 2007. According to Per Jahre Nilsen, the class society's business development manager (well intervention), the development project created some unique challenges.

‘At the time, there wasn't a lot of useful data out there to help us develop the right approach,' he recalls. ‘But based on our experience, technical research and feedback from the industry, we concluded that if the unit is capable of taking control of subsea equipment, such as opening or closing valves on a producing well, it would be classed as offshore, not maritime.'

Nilsen says that these criteria are consistent with the way many national authorities differentiate between offshore operation and maritime ships/vessels operation and notes that MODUs code compliance applies to offshore. Once developed, the new rules were then submitted to external hearings for review and additional comments were solicited from owners and operators.

Class notation
Today, DNV lays claim to being the only class society offering the Well Intervention Unit class notation. Nilsen says that defining the parameters for a mandatory class notation for well intervention units required an exhaustive review of different technical elements and a broad range of safety principles, which covered ventilation, areas classification, shutdown & gas detection, escape, evacuation and communication. The organisation sourced in-house expertise on structural design, which took into account substructure and foundations for well intervention equipment and drill floors when applicable. Other issues included fire protection, dynamic positioning, and a number of supplementary requirements, ranging from gas treatment in the event of a leakage to rescue ladders in the moonpool.

Building on its learnings while developing these new rules, DNV released a new, optional notation known as WELL Intervention in October 2009. The scope of the WELL class notation includes design verification of the well intervention equipment and systems and survey and follow up during fabrication, explains Nilsen. Once completed or certified, the equipment will follow traditional classification principles and be inspected on a regular basis.

‘By introducing the new voluntary WELL class notation together with the revised and mandatory Well Intervention Unit notation, DNV was able to offer owners and operators of well intervention units the same options that owners of drilling units have had in the past,' says Nilsen. ‘We believe the WELL class notation will gain recognition as a mark of quality – an assurance to charterers that the vessel follows internationally recognised standards for well intervention equipment.'

DNV has issued certification for six well intervention vessels, including four optional WELL notations, for a number of subsea services companies. While the commercial benefits for owners sailing with the optional WELL notation are difficult to measure, some well intervention unit operators are hopeful the notation will not only ensure the safe operation of their vessels, but help their bottom line.

Early adopter
One early adopter of the new DNV rules was Aker Oilfield Services. Established in 2006 to meet the rapidly growing global demand for subsea maintenance, the company offers fully integrated services ranging from subsea installation and completion to advanced well intervention operations provided by state-of-the-art monohull well intervention units. An ambitious newbuilding programme is geared to allowing the company to provide subsea intervention, light drilling, and riser and riserless well intervention services.

To date, Aker Oilfield Services has one well intervention unit classed by DNV – the newbuild Skandi Aker. Alf Kristensen, the company's engineering projects manager, comments: ‘While there are many components to winning a contract, we felt the DNV notations gave us an advantage over competing oilfield services companies. The DNV notation helped strengthen the charterer's confidence in our offering and is consistent with our focus on reliability and advanced technology.'

Skandi Aker is a well intervention unit designed for riser based intervention. Kristensen says DNV worked to modify the optional WELL notation to fit their needs. ‘We recognise increased demand for well intervention in deeper water where there is a need for using risers, which allow us to offer coiled tubing services,' says Kristensen. ‘If we see the notation has a positive operational or commercial impact, we will consider working with DNV on other units in our newbuilding programme.'

Looking ahead, Per Jahre Nilsen believes demand for subsea oilfield services will put DNV in a unique position in this growing industry segment. ‘We feel the optional WELL notation has intrinsic value and believe owners will recognise the commercial potential in time – not just for newbuilds, but for existing tonnage.' OE

Categories: Well Operations

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