Redefining Perforation in Sub-Horizontal Gas Wells in Underbalanced Conditions with Slickline Deployment and Smart Coiled Tubing

Abstract

Located in the Arabian gulf, the Qatari North Field is the largest non-associated gas field worldwide with estimated reserves exceeding 900 trillion cubic feet of recoverable gas, or approximately 10% of the world's known reserves. Development of this field present tough conditions for all aspects of well drilling and completion activities. Particular challenges for performing well intervention, which have driven operators and manufacturing and service companies to develop innovative strategies and systematic technology collaboration for intervening these fields in a safe and efficient manner. Recently, two new sub-horizontal wells with multiple reservoir zones needed to be perforated and selectively stimulated. Considering safety factors and operational efficiency, the insertion and retrieval under pressure system was identified as the best alternative to convey an average length of 600ft of 2 7/8-in. guns in single trips with coiled tubing (CT). Although this system has been successfully used in other regions, downhole adverse conditions required specifc components and implementing innovative methods, including the use of 5/16-in. braided slickline for gun deployment, and 2 3/8-in. CT with fiber optic telemetry capability for accurate depth correlation, precise actuation of the firing head system and confirmation of gun detonation. As result of a dedicated planning and preparation process, the two wells were perforated in controlled conditions and each of the applied technologies proved its value. The use of 5/16-in. braided slickline reduced the gun deployment time by at least 2 days from the planned schedule, and the H2S rated connectors and the pressure-pulse firing head gave the confidence to avoid any issues when the perforating assembly was downhole. In respect to the CT real-time telemetry system, this technology provided an exceptional indication of bottomhole conditions throughtout the operation by enabling precise control of the firing head mechanism, identification of gas/water fluid contact in the well, and monitoring of formation response, which eliminated the need for initially planned nitrogen lift operations. This paper describes the selection process of the key technologies deployed for performing CT conveyed perforating operations in two sub-horizontal wells in Qatari North Field, and discusses the workflow developed for those interventions. It then presents case studies and lessons learned and provides conclusions from the experiences gained for performing CT conveyed perforating operations in North Field.