1st October, 2008, Bracknell, UK: Trelleborg CRP - part of the $4.2Bn Swedish Trelleborg AB Group - has announced the development of CFW+, a new high pressure, high temperature crushable foam wrap incorporating Glass Bubbles from 3M, the diversified technology company. CFW+ provides an enhanced solution for the mitigation of subsea well casing failure due to ‘Annular Pressure Build-up’, or ‘Trapped Annular Pressure’. More from www.3moilandgas.co.uk
Says Guy Downie, Manager Subsea Group, Trelleborg CRP: “Our Crushable Foam Wrap (CFW) is typically installed within the B or C annuli of subsea wells, displacing the liquid which becomes trapped in the casing annulus when subsea wells are completed. When heat from drilling and production operations causes the trapped liquids to expand - creating Annular Pressure Build-up (APB) which can exceed 10,000psi - our CFW acts as a mechanical fuse and collapses at a pre-determined pressure and temperature envelope to allow expansion of the annulus fluids and dissipation of any potentially hazardous increase in pressure. If not managed, APB-induced loads can compromise well integrity, potentially leading to leaking fluids or catastrophic collapse of the well casing, halting production.”
“Until now, the operating range of our CFW solution has had typical performance in excess of 4000psi 60-80ºC, which has been sufficient to meet the needs of such projects as the 21 well installation we have just completed offshore Nigeria. However, due to trends in drilling more complex wells, sometimes much deeper and further offshore, we have developed CFW+ which can provide an APB solution for these more demanding situations to temperatures in excess of 110ºC and much greater pressures.”
The operating range of CFW+ has been enhanced due to the modification of the resin system in combination with a range of 3M Glass Bubbles. Trelleborg’s laboratories developed this improved resin, which is also more resistant to water absorption, allowing greater lifetime downhole before utilisation. 3M Glass Bubbles were selected due to their consistency and quality, which contribute to the reliability of the end product.
“As a result”, continues Guy Downie, “Trelleborg manufactures a bespoke CFW+ formulation designed to match the required collapse volume and pressure collapse range specified by drilling and completion engineers for the more demanding deep subsea APB mitigation solutions. This is the only commercially available solution to operate on Temperature and Pressure triggers, rather than just pressure alone.”
Trelleborg has developed this extended range of syntactic foams to assist operators in the busy drilling operations schedule, with potential use on over 100 developments between 2009-2011.
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Trelleborg CRP is the market leader and ‘the’ expert in the manufacture of Syntactic foam systems for use in Subsea applications, with over 25 years track record. CRP Group was the first to develop syntactic foams for use in subsea drilling applications in the early 1990s.
Trelleborg CFW is a polymeric material which has a honeycomb micro structure allowing for compression and ultimately collapse of the system to take place. Trelleborg uses more than 10 grades of 3M Glass Bubbles with crush strengths ranging from 250 psi to 18,000 psi in combination with its resin to create a bespoke formulation and structure tailored to fail at the required pressure/temperature combination as dictated by the well conditions. Normally a pressure envelope of +/-1000psi at a fixed temperature is possible.
CFW is supplied in quadrant cylinders typically one metre long. This allows it to be handled and installed with ease and located anywhere within the trapped annulus while still allowing the free flow of the liquid. The quadrants are installed using a high performance acrylic adhesive.
The amount of CFW specified for a project is dictated by the ‘Collapse Volume’ and ‘Crush Percentage’ requirements within the annulus. The collapse volume is specified by the client and is defined as the calculated volume increase of the annulus fluid brought about by thermal expansion between the installation (or ambient) temperature and the operating temperature. The crush percentage is defined as the amount of compression under isostatic load the foam will allow before catastrophic collapse. This value is usually between 30 – 50% depending on the particular foam formulation. From the collapse value and crush percentage, a total volume of foam required may be calculated. Safety factors are employed during this design stage ensuring target criteria are always reached.
In the drilling start-up phase, the CFW remains in situ, with no significant volume change unless temperature increases beyond the collapse criteria.
As the pressure and temperature in the well rise during operations, the voids within the CFW begin to collapse and relieve pressure in the narrow, confined space of the annulus.
The crush mechanism is progressive in nature over the pressure envelope, but complete failure occurs well before the casing collapse pressure. Typically Trelleborg likes to see the minimum collapse pressure at least 1.5 times the max installation pressure.
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