A Case Study: Adaptation of Integrated Drilling Services Approach and Improved Operational Practices to Drill Linerless Slim Hole Extended Reach Wells in an Onshore Field Abu Dhabi, United Arab Emirates
Authors: Kamble Rahul , Abbas Zaheer , Kirby Clifford , Al Menhali Abdulla Sulaiman , Al Mazrouei Manal , Sas Matthew , Patil Yogeshwar , Gohar Syed 
Published: October 2023

Abstract
This paper demonstrates the integrated approach solutions and best operational practices instituted during a linerless slim hole extended reach drilling (ERD) campaign in a mature oilfield, located onshore Abu Dhabi, United Arab Emirates.
A national Operator and the Integrated Drilling Services (IDS) team recognized that optimization of the well construction process was required to drive efficiency and cost-effectiveness in a competitive oilfield market. The operations team of the company modified the existing ERD well designs to linerless extended reach designs with 15,000 ft slim hole (6-1/8") horizontal sections.
Integrated Drilling Services (IDS) provided a unified method of channeling multi-disciplinary solutions and technologies to ensure high quality planning and risk management, optimized execution strategies and knowledge capture. In this campaign, three linerless design trial wells were drilled and completed successfully. The wells were designed with a particular focus on the geological challenges presented by a carbonate formation in the onshore field. The carbonate reservoir comprises multiple layers with porous intervals separated by dense layers. The linerless trial phase targeted the shallowest zone in the field, with the aim of providing complete zonal isolation of the formation behind 9-5/8" casing, thus minimizing operational risks associated with the pressure regimes and avoiding sustained annulus pressures during the well life cycle.
A unique concept of the linerless well design is the slim hole 6-1/8" hole section across the interbedded reservoir layers, which presents its own challenges in terms of drilling the section in a single run. The use of application-specific technology and improved operational practices provided solutions for the known, field-specific downhole operational issues, including wellbore temperatures, torque and drag limitations due to slim hole drill pipe sizes, Equivalent Circulating Density (ECD), wellbore stability, hole cleaning and stuck pipe. Technological changes were implemented, including the utilization of newly developed spacers and cement slurries to achieve competent cement behind 9-5/8" casing for reservoir sealing, the use of circulating subs across open and cased hole at higher rates than normal for slim hole sizes, and best in class lubricants in reservoir drilling fluids to reduce the friction factor and aid the drilling of the slim ERD hole section and subsequent lower completion run.
Of the three trial wells, two wells were drilled ahead of planned time. This method has provided an opportunity to drill and complete wells within existing equipment-rating envelope.
Adoption of integrated drilling services, modified well designs and implementation of best drilling practices have projected a step change in improving well delivery time compared to conventional offset ERD wells. Furthermore, the changes implemented provided a way forward for efficient project economics in competitive market conditions, reducing time and subsequently development well costs in a mature field.