A Next-Generation, Fully Controllable Alloy Wellbore Sealing Technology

Abstract

Sealing wellbores via the use of alloy sealing technology presents a number of challenges. The typical approach involves the use of exothermic chemical reactions delivering high temperatures to ensure sufficient heat is generated to ensure the alloys remain molten for long enough to reach their intended radial extent. One challenge of such an approach are the high temperatures generated and their potential effect on the external well barrier elements (casing, cement, formation). Furthermore, chemical methods are a ‘one shot’ approach that do not permit close control or repeat of the heating the process after initiation. A next-generation alloy placement system has been developed using an electrical heater, cable and deployment system with sufficient capacity to deploy a fully controllable and verifiable heating solution, capable of operating at lower temperatures for extended durations. This allows close control of heating cycle to prevent damage and optimise the process, resulting in a superior barrier envelope. Furthermore, rigorous design and testing ensures the minimum amount of expensive alloy is used to achieve the desired seal. This paper details the extensive design and testing programme that was undertaken to devise an optimal alloy plug and mature a complete barrier system that challenges both conventional approaches involving cement, and first-generation alloy plugging technologies. The project culminated in a full-scale pilot in a test well that replicated the challenging wellbore environment of the intended application as closely as possible. The testing demonstrated that the technology is capable of setting a competent alloy barrier to deliver at least a 3,000 psi / 207 bar differential pressure ‘big bore’ seal, even when set in drilling fluid and flowing gas.