Successful and Unconventional Coiled Tubing Intervention for the Complex Re-Abandonment of a Slant Gas Well in Brazil

Abstract

Abstract

Abstract In 2014, in northeastern Brazil, a slant well experienced a kick while drilling the 8.5-in. section, which required full well-control operations and subsequent plug and abandonment (P&A) after the drillstring became stuck. Post-abandonment integrity tests revealed continuous gas migration through the 5-in. drillpipe (DP), 9 5/8-in. casing (CSG) annulus. Because of the complex challenges to re-abandoned a slant well, coiled tubing (CT) was essential to achieve effective wellbore isolation, as required by the national regulatory agency to secure the extension of the field's production license. Based on injection test results, which confirmed micro-channeling in the annulus, well history, and detailed site assessments, a multidisciplinary team in close work with the operator developed the following two-part strategy. Operational Requirements Design and deploy a custom CT structure to support all phases of the intervention (rigup, bottomhole assembly (BHA) changes, operation, and rig down) adapted to limited surface space, aligned with an inclined well xmas tree, and executed under a strict, step-by-step protocol. Technical Requirements The custom rigup was executed successfully for this unconventional slant wellhead with no compromise to safety or quality. A 90-m cement section was milled in 12 runs using four different bits [including an expandable underreamer with rate of penetration (ROP) ≈ 0.3 to 3 m/min)] to overcome challenges, such as unknown inner DP geometry, steep inclination (60 to 90°), and high cement hardness. Four sand jetting cluster perforations [83 to 86 m, 6 shots per foot (SPF)] achieved 1:1 communication between the DP and CSG annulus. A subsequent cleanout confirmed formation fluid entry points and kept the micro-channels as free as possible for cement placement. Finally, because of limited volume at a depth of 90 m, a bullheading cement operation was performed and full zonal isolation was achieved. The versatility and reliability of CT were crucial in overcoming the technical and logistical challenges of this complex re-abandonment on an inclined well surface structure. The successful intervention allowed the operator to comply with regulatory requirements and proceed with the field's production and expansion plans, avoiding significant delays and costly alternatives.