26TH – 27TH JUNE 2019, ABERDEEN EXHIBITION AND CONFERENCE CENTRE
UK-based Rawwater Engineering Company Limited has created the world’s first ‘anticipated’ 3,000-year-life underwater cast metal seal. The metallurgy has been certified by Bureau Veritas as fit-for-purpose for extreme life applications in the oil and gas industry and qualified to the VO (highest rating) of ISO 14310.
“At the 9th Society of Petroleum Engineers’ (SPE) Well Abandonment Symposium, we will be presenting research which underpins our belief that the development of bismuth alloys provides the opportunity for a significant reassessment of current approaches to well abandonment in particularly challenging applications, including resealing failed abandonments,” comments Rawwater managing director, Dr Bob Eden.
Recognising the need for a specialist alternative oil well plugging medium to cement, Rawwater has been investigating the use of bismuth alloys as a plugging medium for almost twenty years. Over that time, the organisation has built a large corrosion and creep database regarding the use of underwater cast bismuth alloys. Rawwater invented the Bismuth Plug and has completed in excess of 100 workshop trials using novel alloys specifically formulated for plugging and abandonment – recording a zero failure rate throughout the programme. Rawwater’s trials also included the successful deployment of bismuth alloy seals in two onshore wells in Alberta, Canada, at 1000’ depth and 1000psi pressure differential.
Rejecting common bismuth alloys, Rawwater has produced a suite of proprietary expanding metal alloys for use as high integrity seals in oil well abandonment. The alloy properties of low melting point and expansion upon solidification enable these high integrity seals to be cast in-situ, without the inherent creep issues typical of bismuth tin.
To achieve offshore capability and extreme reliability, Rawwater recently completed a two-year programme to deliver 7” alloy plugs for deployment in the North Sea, rated to 6000psi differential pressure at 60cm (2’) in length. Extensive development and testing was conducted in collaboration with an operator consortium and the UK Government to develop the formulation of the metal seals. To establish the mechanical properties and creep behaviour of the alloy under service pressure and temperature conditions, Rawwater partnered with the University of Aberdeen, through an Oil & Gas Innovation Centre (OGIC)-funded partnership.
The result of Rawwater’s research is a suite of alloys for onshore, offshore and subsea plugging and abandonment, with operating envelopes to cover downhole geothermal temperature conditions from 158 -194F (70 – 90°C) and 284 – 320F (140 – 160 °C). These alloys have been subjected to a strict technical qualification programme overseen by Bureau Veritas, with stringent adherence to the qualification processes stipulated by DNV-RP-203 – Jul 2013, ISO 14310 (V0) and Oil & Gas UK. They are intended as a cost-effective alternative for sealing well abandonments and resealing failed abandonments that were previously plugged using cement. The application includes both casing plugs and plugs/seals in undefined and/or rough walled geometries (e.g. cap rock) that are difficult to seal with existing technologies such as cement.
“I am in no-doubt that other organisations are striving to develop alloy-based alternatives to cement-based plugs, which meet the 3,000-year design life specified by Oil & Gas UK for plugs in the North Sea,” adds Dr Eden. “It is fair to say, however, that our strength lies in knowing the specific circumstances where such alloys can be used, as well as where they cannot. At the SPE symposium, I look forward to demonstrating how, through the use of the correct types of bismuth alloy, operators can benefit from long-term plug integrity, longer plug life and significantly reduced deployment costs – a factor that is even more significant offshore, with plugging taking only a matter of hours and not requiring the use of a rig vessel.”
Low melting point alloys such as bismuth can be applied easily with little heat input to the substrate and expand on solidification to form a very tight seal. The low viscosity of the molten alloy enables penetration into porous substrates with pore throats as tight as 25 microns, with expansion on solidification giving a tenacious gas-tight seal. The high density of the alloy displaces water to enable sealing underwater or against large leaks, while at the same time being easily removable by remelting if required. The bismuth casting process takes hours, as opposed to days for cement to set. As an example of the capabilities of bismuth alloy, a 3' (0.91m) bismuth plug can outperform a conventional cement seal, which - by comparison - may be up to 500' (approximately 150m) in length.
From its technology centre in Warrington, UK, the Rawwater Group provides solutions to the oil & gas industry. The group offers contract research and consultancy in the fields of materials science, well technology and water management, and combines engineering with reservoir microbiology to deliver solutions for facilities design, oilfield souring, biofouling and microbial corrosion.
The Rawwater Group’s engineering division is known for its expertise in the development and application of molten bismuth alloys as a specialist alternative to cement for sealing within onshore and offshore oil and gas wells. The division is also creating a range of new alloys to provide secure, high integrity, reversible metal seals for the nuclear industry and other sectors.
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