Improved Magnetic Ranging Tool Assisted Milling for Wells with Casing Deformation and Misalignment: A Case Study in Mature Oil Fields

Abstract This paper introduces an integrated system that combines magnetic ranging and milling technology for wells with casing deformation and misalignment. Many mature oil fields, such as Saudi Arabia's Ghawar Field and the North Sea Field, have entered a decline stage. Extended exposure to perforations, fluid corrosion, and formation movements has led to various forms of casing deformation and misalignment. These issues disrupt the original well network, and allow oil and water to migrate through the broken casings into upper formations or even to the surface, significantly impacting water injection development. To maintain stable production in mature oil fields, conventional methods such as directly squeezing cement at the breakpoint often fail to achieve satisfactory sealing results. Additionally, techniques like pulling the casing or repair operations are costly and can lead to more complex downhole accidents. Therefore, there is an urgent need for more efficient disposal methods to address the challenges of abandoning and disposing of old wells with deformed casings and reconstructing well networks in mature oil fields. The system first uses improved magnetic ranging tool to determine the direction and distance of the Misaligned casing. A directional drilling assembly then adjusts the trajectory to avoid the misalignment points and casing joints, connecting with the lower intact casing at a minimal entry angle. After successful connection, larger-bend-angle screws and PDC bits, or tools such as reamers or milling cones, are used to grind and create windows in the casing. Smaller drill pipes or coiled tubing are subsequently deployed to re-enter the lower casing, extending into the caprock where cement is injected under pressure, and the well is shut-in for sealing. Finally, perforating shots are fired at the breakpoint, followed by large-scale cementing back to the surface to complete the upper sealing. The application of this system in mature oil fields in eastern China demonstrated its effectiveness. Long-distance accompaniment was achieved, and multiple connections were successfully made, with the results verified using downhole monitor. Cement squeezing was performed according to the established procedure, and the entire block saw a production recovery of 4 tons per day. The improved magnetic ranging tool assisted milling system offer a novel solution to enhance well network reconstruction and ensure sustainable production in mature oil fields.