Feature 1 | RULES AND REGULATIONS

Well Intervention Units: faster, deeper, cheaper

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

has experienced a boom in the past decade. According to consultants Infield Systems and Douglas Westwood, the total number of subsea wells will balloon 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

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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, use more complex tie-back solutions and improve recovery rates for aging wells, which are about 10-20% less than platform wells. Tese 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, screens), re-perforations, zone isolation, fluid sampling, PLT, chemical treatment and well abandonment, among other services. In the past, this work was performed by

mammoth, slow-moving semisubmersible drilling rigs. However, developments in dynamic positioning systems, ROVs and other specialised onboard systems has allowed well intervention equipment to be placed on mono-hulled units, which can move quickly from one well to the next, helping to reduce chartering costs

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riven by the insatiable global demand for energy, subsea exploration and well construction

and improving well recovery rates by up to 50%. Riser well intervention units are still preferred for some kinds of work and in depths below 500m, but new composites now being developed for wire lines may soon allow RLWI units to work in deeper waters.

A vessel or an offshore unit?

Te first monohull well intervention unit (Seawell) was built in 1986 by WellOps. Te concept proved a success, and over the next ten years, demand for LWI units grew. However, because these units are oſten similar in design to offshore supply, support or multi-purpose vessels, there was uncertainty on how to class them: Are they vessels or mobile offshore units?

“the optional WELL notation has intrinsic value and believe owners will recognise the commercial potential in time not just for newbuildings, but for existing tonnage”

Based on its extensive experience in the

North Sea offshore industry (home to about 40% of the world’s subsea wells) and other regions, Det Norske Veritas (DNV) moved quickly to manage these issues. According to Per Jahre Nilsen, DNV’s business development manager (Well Intervention) the development project, which began in 2007, created some unique challenges.

“At the time, there wasn’t a lot of useful

data out there to help us develop the right approach. 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 said. 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 mobile offshore development units (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.

Unique offering

Today, DNV is 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, shut down and 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. Based on experience gained by developing these new rules, DNV released

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