On a Malaysian offshore platform, gas migration from the casing annulus of a well led to the release of a gas cloud, accompanied by the surfacing of water and mud through the casing. This situation necessitated a cessation of all production activities. To address this situation, the decision was made to implement the innovative BiSN “Perf, Wash, and Bismuth (PWB)” technology for the well’s Plug and Abandonment, marking a first-of-its-kind application worldwide. The new process proved to be 75% more efficient than traditional P&A methods used elsewhere by the operator, giving substantial savings.
The main challenge was to secure the well’s integrity to prevent future leaks and ensure safety. Traditional cement plugs used in P&A were deemed insufficient due to the complex nature of this particular well. The unique challenges included handling the well’s legacy status (drilled in the 1980s) and managing operational limitations due to the platform’s structure and available equipment.
The Malaysian operator undertook a thorough analysis and determined that employing the Perf, Wash and Bismuth technique would be the optimal solution to provide a permanent seal. This technology involves perforating the casing, washing the area, and then deploying bismuth-based alloy that solidifies to form a robust, gas-tight seal. The operation required precise coordination and innovative engineering, particularly in overcoming the physical constraints of the HWU rig, such as limited crane capacity and deck space.
BiSN’s bismuth alloy was the perfect barrier material choice due to short plug length, 6 feet, rather than the traditional method of setting a 120-foot conventional P&A barrier. Although substantially more compact, bismuth alloy provides superior sealing integrity than other materials.
In many applications wel-lok™ bismuth P&A plugs are set within a section milled window. The operator made the strategic decision to use the Perf, Wash and Bismuth technique to create efficiencies with the hydraulic workover rig. Rather than a 20-foot section mill window, a 6.2-foot casing perforation run was conducted followed by precise cement removal through high efficiency washing. The perforation run was designed to achieve the highest open area possible to allow the liquid bismuth alloy to flow through the casing well bore and into the open hole annulus.
By eliminating the section milling part of the operation, significant reductions in rig time and HSE exposure were achieved.
The operation successfully placed three Bismuth plugs within the well, effectively sealing it and restoring integrity with a zero psi surface casing measurement. This innovative application not only secured the well but also enabled the platform to safely resume production. The absence of pressure within the annulus post-operation confirmed the effectiveness of the plugs.
The successful deployment of the “Perf, Wash, and Bismuth” technology provided several key insights:
This case study illustrates the potential of advanced materials like BiSN bismuth-based alloy in improving the outcomes of P&A operations, especially in challenging environments. The lessons learned from this project can guide future applications and developments in the field, setting new standards for well abandonment processes.
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