Preparation, Execution, and Associated Challenges for Utilizing the First Successful Closed Loop System Methodology Worldwide in Underbalanced Coiled Tubing Drilling in ADNOC'S Fields

Abstract

Abstract Due to the declining reservoir pressures in some of its onshore gas carbonate fields, Operator decided upon an initial 3-wells UBCTD, (Underbalanced Coil Tubing Drilling), a campaign in its onshore fields, The objectives of these operations were to evaluate the applicability of the technology in these fields, to understand requirements and methods of the technology and to evaluate the benefits of drilling the target formations in an underbalanced mode. During the planning phase, the Operator conducted a feasibility study that flagged potential limitations to deploying UBCTD operations in existing wells, due to limitations on the completion design and other factors. All of this resulted in the plan to drill fit-for-purpose wells to the top of the target reservoir to facilitate the deployment of the technique. These wells were completed with 5.5/4.5 in. Tubing and 7 in. Liner and left with a 100ft open hole interval from where CT drilling operations would later continue. The results ofthe feasibility study nevertheless, additional detailed engineering work was performed in all aspects of the design by the operations team to ensure the success of the trial, including a review and validation of the available data and the feasibility to deliver the stated objectives (lateral length, underbalanced conditions, minimal flaring operations, drilling fluid re-circulation, etc.). As a result of this approach, all three wells were successfully drilled in underbalanced conditions and to the target lateral length of 4,000 ft. Well, placement was facilitated using Biosteering techniques and continuous monitoring of the well performance vs. drilled footage, allowing steering decisions to be made in real-time to maximize the production of each lateral, resulting in outstanding production results of 3x sustainable production of similar wells drilled conventionally, (after stimulation). This paper describes the key engineering decisions and assumptions taken during the design process, as well as methods applied during the drilling operation to achieve the best well’s performance. The lessons learned from the project will serve as a launching pad for planning and efficiency gains for future UBCTD operations in the region.