Case History: A New Approach to Section Milling: Leaving the Swarf Behind!

Abstract

Abstract Section milling is a method used in plug and abandonment operations to remove casing over a specified interval, enabling a barrier to be placed for complete isolation across the wellbore. This method is preferred and often required when an annulus behind a casing string is not properly isolated and cannot be appropriately remediated by conventional methods such as cutting and pulling the casing, or squeezing cement through perforations. Section milling and placement of a rock-to-rock cement barrier is a highly effective method for achieving proper wellbore isolation for plug and abandonment. However, this method poses unique challenges that can result in lengthy, complex operations and high costs to operators. A key challenge faced when removing high volumes of casing (up to and exceeding 50 meters (165 ft.) per interval), is circulating the generated steel cuttings (swarf) out of the well, and safely capturing and disposing of them. Much of the time spent on section milling operations is dedicated to mitigating the health, safety, operational, and equipment risks associated with the removal and handling of swarf in the well and on surface. These challenges inspired a joint operator/ service company project to develop a method of section milling that would deposit swarf into the wellbore, creating a unique, and in-situ approach to debris management that reduces risk and costs to the operator. The prototype section milling system was extensively tested, with final, full-scale tests performed in a drilled and cased hole from a fully functioning land rig. Conclusions from the final test well operations yielded favorable results, resulting in a final system design that was qualified for field use. Currently, the system is in final preparations for its first field deployment, with candidate wells identified and equipment ready for use. First planned operations are scheduled for a platform well on the Norwegian continental shelf. This paper will detail the final testing phases, field trial preparations, and candidate well selection leading up to the first field deployment of a first ever ‘swarfless’ section milling system.