A metal alloy that has a similar viscosity to water in its molten state and then solidifies rapidly in a gas-tight closure has recently reached its 300th deployment at the bottom of the well. This is according to a new announcement from UK-based BiSN Oil Tools which develops bismuth caps for a range of applications.
Founded in 2011 and backed by BP’s venture capital unit, BiSN said oil and gas companies around the world have used its innovation in places where they might otherwise use cement or elastomers. Established use cases for onshore and offshore wells include permanent well abandonment, repair of casings / pipes, and closure of water or sand production areas.
BiSN’s technology hinges on a customizable alloy composed primarily of bismuth and tin, whose respective elementary abbreviations of Bi and Sn form the company name.
The company’s proprietary alloy is sent in a solid state as a jet around the outside of a heating system. The thermal element is made up of termite, a compound of iron oxide and aluminum powder, which only needs a small burst of energy delivered via an electrical line to trigger a chemical reaction.
Once the heat reaches a predetermined melting point, the bismuth-based alloy begins to flow. BiSN said the liquid alloy will go anywhere in and around the well where water can flow. This includes perforations, screens and the ring.
BiSN described the solidification process as “almost instant” as the alloy changes from a liquid to a solid as soon as its temperature drops below the melting point. During this transition, the alloy expands similarly to how water does when it cools to ice.
This all takes just a few minutes and within hours the well is ready for a pressure test to see if the seal holds.
BiSN claimed to control the melting point and heat of its termite system using damping and binding chemicals. This prevents the exothermic reaction from creating temperatures that would damage the well shell or its completion components. The upper limit used by BiSN for its caps is around 300 ° C (572 ° F), while the casing can begin to degrade due to excessive heat above 800 ° C (1,472 ° F).
Connecting a billion-barrel field
The largest abandonment work BiSN has undertaken so far has been the focus of a case study presented at this year’s Offshore Technology (OTC) Conference in Houston. In OTC 31897the authors of BiSN and AkerBP shared details on how 35 bismuth plugs were used to plug and abandon (P&A) 30 wells off southern Norway.
The P&A campaign was carried out at the Valhall oil field, discovered in 1975 and which has produced more than 1 billion BOE in the last 40 years. AkerBP wants to produce another billion BOEs from the field over the next 40 years. To do this, he had to plug all the original wells so that he could drill new ones.
A highlight of the P&A project includes the use of the largest bismuth cap ever made. This is according to BiSN and AkerBP who noted in the paper that the record-breaking plug measured 50 feet in length and weighed nearly 34,000 pounds, of which about 20,000 pounds comprised the bismuth alloy.
During the 30-well project, BiSN and AkerBP reported that 350 tons of bismuth alloy was sent to the downhole. The technology has been credited for helping AkerBP reduce its original P&A timeline from 10 years of operational time to 4 years.
This followed the first P&A campaign conducted in 2014 that used conventional sealing technology. After that first attempt to seal the wells, 14 showed no signs of annular gas pressure. However, the situation has become more troubling over time.
By 2019, the number of wells with zero pressure buildup had shrunk to just four.
It was around that point that AkerBP attempted to qualify BiSN technology with a 2-year test inside a well with one of the highest sustained envelope pressure levels.
Downhole indicators showed that the upper section of the annulus where the first bismuth plug was used had a reading of 0 psi for the duration of the 2-year monitoring effort. Downhole cameras were also used which provided visual confirmation that no gas bubbles were flowing past the location of the plug.
Due to its non-corrosive nature, BiSN has found that alloy caps should last for many thousands of years. This is based on the laboratory results cited in the company’s technical paper which suggest that the lifespan of the caps can even exceed 100,000 years.
For further reading
OTC 31897 Bismuth plugs used to plug all wells during the final phase of the abandonment campaign in Valhall DP, offshore Norway by Egil Thorstensen, Kjetil Vadset, Martin Knut Straume and Laurent Delabroy, AkerBP; Gasser Abdelal, Queen’s University, Belfast; Paul Carragher, Jeff Fulks and David Leslie Mason, BiSN Oil Tools Ltd.