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Section milling is a common method for casing removal during well abandonment applications where annular well integrity is compromised or questioned. The removal of casing by milling a window provides full access to the virgin formation, enabling placement of a rock-to-rock barrier. Retrieving the metal cuttings (swarf) created by the milling process to surface and handling them on surface is a time-consuming and costly operation associated with health safety and environmental (HSE) risks. A joint operator/service company technology development project of a section milling without swarf to surface system now provides a novel solution. This paper discusses the design, lab-testing and wellsite testing iterations that led to a fully functioning system for establishing a true rock-to-rock barrier without the nuisance of swarf at surface. The new method entails milling in an upwards direction away from the swarf deposition. Currently, all section milling operations mill downwards. The system consists of the following components: taper mill, auger, section mill, emergency release disconnect, jet sub, left-hand rotating mud motor and torque isolation assembly. The concept of milling upwards, mandated left-hand rotation to prevent casing couplings from backing off, paired with the desire to deploy on right-hand drill pipe resulted in designing and manufacturing of a custom-built left-hand mud motor. Developing a capable torque isolation assembly was not without hurdles; excessive vibration during early tests led to significant improvements to the torque isolation system, which now provides a robust solution. Creating the swarf proved to be the easy part. Downhole swarf management was more challenging, and an auger system was developed to mitigate the earlier issues encountered. Multiple tests, evaluation and step-by step system improvements ultimately culminated in a fully functioning system, now ready for its first field deployment. A more efficient and cost-effective removal of casing by downhole deposition of the swarf created from the casing section milling operation, will reduce operational time related to plug and abandonment (P&A) operations. Multiple enabling technologies provided the stepping stones for this system and will be highlighted individually. |
