A Novel Approach to Qualifying Bismuth as a Barrier Material

The barrier material conventionally used for permanent P&A is cement. Since two barriers are a requirement to properly isolate potentially flowing formations, the reliability of the barriers could be enhanced by introducing a second barrier material. Application of two distinct barrier materials with differing sealing and failure mechanisms will promote a higher level of independence between the barriers.\nQualification of bismuth as a barrier material provides operators with an alternative to cement. Bismuth is a metal with such unique characteristics making it tailor-made for P&A applications. For instance, the required plug length is significantly reduced compared to the current length requirements for cement plugs. Thereby, costs are reduced. This thesis defines why bismuth is such a suitable barrier material for permanent P&A, in addition to addressing risk related issues.\nAker BP has together with BiSN initiated a verification process to verify bismuth as a barrier material inside cased hole. BiSN is utilizing thermite technology to melt a bismuth based alloy downhole, creating a fully impermeable metal-to-metal sealing plug after solidification.\nThe verification process presented in this thesis targets a bismuth plug sealing inside a 20” casing, without having to retrieve the 13 3/8” casing. Full scale testing was performed with various learnings to optimize the final design parameters, before conducting a field installation. The field installation, thoroughly described step by step in this thesis, was performed to verify the bismuth plug in an offshore well. This is the worlds first bismuth P&A barrier plug ever installed, and by far the largest considering its geometry.\nBased on the results presented in this thesis, a proposed EAC-table for a bismuth plug has been produced to describe the function, necessary requirements and verification for future bismuth plugs.