Drilling risers

TCP for deepwater drilling

Investment in oil and gas exploration has turned a corner this year, with growth expected to remain at a steady 6% in capital expenditure for the next 6 years (source: Rystad Energy). Minimising cost remains the key focus for operators and with 70 to 80 percent of the cost of well drilling and completion being time related (source: McKinsey) any reduction in delivery time has a direct benefit to the bottom line.

The latest ultra-deepwater drilling vessels require high payload capability, high tension capacity and the latest generation riser systems to achieve a workable operational envelope. As depths increase beyond 3200m and operating pressures increase to 20ksi the problems associated with increased riser weight become so great that weight reduction becomes crucial. One method of weight reduction is the use of m-pipe® for kill and choke lines as these currently constitute almost 35% of the riser weight. The reduction in weight allows simpler handling, lower top tensions and reduced buoyancy. This improves safety, lowers time to first oil and allows consideration of lower day-rate vessels and advances in drilling riser technology.

Transocean carbon fibre composite trial

Transocean is a leading international provider of offshore contract drilling services for the oil and gas industry. The company specialises in technically demanding sectors of the global offshore drilling business with a particular focus on deepwater and harsh environment drilling services.

Transocean evaluated a range of technologies that offered the potential for weight reduction of deepwater drilling risers including metallics and composites. Transocean’s analysis of substituting the steel auxiliary lines with carbon fibre pipe indicated a 30% reduction in riser weight while also maximizing the operation window and avoiding downtime.

The company concluded that Magma’s m-pipe held the best potential for successful implementation due to the combination of performance properties and end fitting design. We have been working together since 2012. This case study explains the work we have completed together and what is currently in progress.

Incremental technology adoption

As part of a program of technology development and qualification Transocean began by becoming familiar with carbon fibre pipe on a project for three m-pipe booster lines. The objective was to test, monitor, and evaluate m-pipe for use as future 15 and 20ksi kill and choke drilling systems. These were manufactured as 7.5ksi 4 ¾inch boost lines complete with end fittings to interface with a standard drilling riser joint. This enabled in-situ testing measured the mechanical performance of the boost lines when integrated into the drilling riser. The boost lines included sensors to monitor axial, bend and hoop strain.

In addition to weight savings, Transocean believed the robustness of the product could reduce the attrition rate from corrosion and damage. The smooth bore of m-pipe gives improved kick detection and circulation, or the ability to reduce the pipe diameter. The smaller diameter then reduces the interface loads on adjacent packages such as BOPs, wellheads and tensioners and reduces drag in high seas, helping to maintain acceptable top and bottom angles and reducing cyclic loading, thus minimizing fatigue damage.

An enabling technology for a simpler drilling riser system

On the back of this project and with increased understanding of carbon fibre materials technology, Transocean realised the potential impact m-pipe could have on its technology roadmap. The company then began working on a novel drilling riser system that could be rapidly deployed with the risk reduction bonus of hands-free operation.

Risex is Transocean’s patented twist and lock ‘undressed’ drilling riser. The company calculates that Risex will cut deepwater well installation time by around 2.5 days and improve safety due to hands-free deployment. It will also benefit from enhanced operability due to reduced riser mass, which will mean less buoyancy and drag.

Risex is rapidly deployed and is coupled to continuous spooled auxiliary lines which must be highly robust yet flexible. Transocean proposed to complete a trial deployment of a continuous open water auxiliary line on Transocean Discoverer Clear Leader in the Gulf of Mexico in November 2017.

The trial

The field trial was undertaken to demonstrate that m-pipe could withstand the required loads and behave as needed as an open water auxiliary line. An LMRP was lowered to 4000 feet using a conventional drilling riser. m-pipe was reeled out from Magma’s Integrated Deployment Package (IDP) at a pace of 2,750 feet an hour at 70% speed. The auxiliary line was connected to a reconfigured LMRP termination using an ROV in under two minutes. Magma’s m-pipe was then tensioned to ensure non-contact with the riser. The trial demonstrated that m-pipe remained “stout, tolerant of compression and clashing”. It held its position 30 feet off the riser throughout in a range of current conditions.

Charles Tavner, Magma Global COO, said: “It was fantastic to see first-hand m-pipe behaving exactly as we said it would do. No pipe has been up to this job before as they are either not flexible enough to spool or not strong enough to withstand the tensions required. We look forward to the next phase of this collaboration.”

The flexibility required to spool the pipe for transportation and deployment, coupled with extremely high demands in tension strength, led Transocean to conclude that m-pipe is currently the only pipe available that can meet its requirements for auxiliary lines for Risex.

Current programme

The Risex trial in 2017 successfully de-risked the design architecture. Magma now has an exclusive partnership with Transocean for the development and supply of the continuous spoolable composite auxiliary lines for deepwater drilling.

Transocean is currently developing the other Risex components for use on a future vessel.

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