Bernard Herman van Bilderbeek, CEO of Plexus Group, explains how its friction-grip technology can be applied to subsea wellheads
Since early 2000, the US Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE), formerly the Minerals Management Service (MMS), has considered the impact of sustained casing pressure (SCP) on the safety of offshore operations in the Gulf of Mexico.
A detailed survey of operations disclosed that the vast majority of surface wells at some stage experience SCP, and in 2002, the MMS concluded that if such incidence occurred on platforms, then the same things must be happen- ing subsea. However, the fact remains that subsea wellheads – although similar in design to unitized surface wellheads – do not have outlet valves through which events in the various casing annuli can be monitored.
Image Caption: A POS-GRIP clamp can be configured to squeeze the outer pipe so that it grips the smaller pipe inside.
Image courtesy of Plexus Ocean Systems Ltd.
Effectively, subsea wells are “out of sight, out of mind” where it comes to annuli, and as a result, the MMS did not have data to back up its supposition. The agency did conclude that SCP is a threat to operations and the environment, and statistics show that it has a point. In 2002, the MMS asked US operators to do something about subsea annulus management. After years of “toing and froing,” it was concluded that the available solutions were too complex, involved too many additional risks, and were too expensive in the long term. The MMS abandoned the project in December 2005. In its final report, it lamented that subsea monitoring would only come about through regulator intervention.
Fast forward to 2013, and suddenly, at least in the UK, the quest to stop “flying blind” is once again rearing its head in the form of a call for solutions by UK industry organization ITF.
Following Macondo, Plexus Holdings was asked by a group of operators to study the application of its patented friction-grip technology to subsea well- heads. As a direct result of this inquiry a joint industry project (JIP) was formed, supported by major operators, including Shell, Wintershall, EIN, Total, Tullow and Maersk. The project is now 18 months underway with the aim to come up with a new approach in wellhead engineering, focused on addressing the systemic shortcomings of conventional subsea wellhead techniques, as exposed by Macondo.
The problem is the limited amount of energy one can remotely deliver subsea through the drill string from thousands of feet away. Ten thousand feet of drill pipe feels like a rubber band and inside the bore of a wellhead space is limited. Yet an enormous amount of energy is needed to clamp moving parts together and to energize metal seals so that well forces cannot cause hangers to move and seals to fail over time.
On the surface HPHT wells mainly use wellheads that are clamped together so that the force generated between inter- connecting flanges can be used to hold things firm.
This approach cannot be done subsea, where loose fitting lock rings, often a source of trouble, are used to hold things together.
A better way was necessary, and thus, the HGSS subsea wellhead JIP came into being.
From the start, the project was designed to solve the subsea casing hanger lockdown problem. With Plexus friction-grip technology far more energy is available than required, even subsea.
The technology uses massive hydrau- lically power rings on the outside of the wellheads, which crimp the wellhead body inwards until it grips and seals the casing hanger and holds the casing. This arrangement is instant and timeless, as fit cold welding the pieces together, although it happens within the materials elastic range and is fully reversible.
Simple, releasable, rigid and most importantly reusable, which is the tech- nology can be used to solve the perennial subsea annulus access conundrum.
In fact, Plexus is so sure about the fea- sibility of its system that it made subsea monitoring, bleed-off and remedial capability one of the ultimate goals of the HGSS JIP.The solution works as fol- lows; porting is provided past the casing hanger and internal to the wellhead body. As these ports terminate above the casing hanger in the wellhead bore a seal sleeve, similar to a wear bushing, is located across the ports in an area of the wellhead that can be shrunk inwards with the externally fitted POS-GRIP® gripping rings. Once fully energized, the seal sleeves provide metal-to- metal bump seals on either side of the monitoring port gallery. All this is done within the elastic range so that, once released, the sleeve can either retrieved or moved down (Plexus is still working on this one); the ports can be directed into the subsea tree, through the tubing hanger, thereby allowing a continuous peek in the B and C annuli, depending on requirements. OE
Bernard Herman van Bilderbeek is Chief Executive Officer of Plexus Group. He has more than 35 years’ experience in engineering and management roles and previously held senior positions with Vetco Offshore Industries, Dril-Quip, and Ingram Cactus. In 1986, he founded Plexus and went on to merge the wellhead division of his company with Ingram Cactus, where he became President Eastern Hemisphere.
In 1996, van Bilderbeek regained the Plexus Ocean Systems Ltd. name through which POS-GRIP technology was invented, developed, and com- mercialized for the oil services wellhead equipment market. Van Bilderbeek earned a BS in Mechanical Engineering from Southern Methodist University in Dallas.
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