Extended Reach Lower Completions: Enhanced Operational Performance and Efficiency
Authors: Cannon Geoff David , Caproni Cristiano , Kulkami Neeraj Mukund , Al Yammahi Ohoud Abdullah , Al Hajri Saeed Salem , Al Harbi Ahmed Abubaker , De Barros Adelson Jose 
Published: October 2023

In 2021 the Drlling Team assigned to a significant Field Development Offshore Arabian Gulf, achieved a major milestone by installing the longest 6-5/8″ lower completion in an aqueous fluid (viscous brine). The aqueous fluid is solids free with lubricants added to greatly improve friction coefficient and the clean-out efficiency of the drilling mud. This method saves ∼5 days operational days by eliminating an inner string clean out post installation of the Lower Completion.

This achievement is the culmination of a 5 year journey of delivering over 70 Production wells in this Field. Through this journey a "Technology Staircase" has evolved and matured - particularly related to reservoir drilling and installation of the lower completion.

The first Maximum Reservoir Contact (MRC) pilot wells in the field were drilled and completed in 2020. Both these wells were completed conventionally with 6-5/8″ lower completion ∼13,000ft run in Non Aqueous Fluid (NAF). The challenge was to optimize these proof of concept (pilot) completions by taking the large step to run them in aqueous fluid as pioneered and proven with 4-1/2″ lower completions. All groups within the drilling team were challenged with the task of analyzing the collected historic data and apply it to our software models. Our target was to have an engineered confidence that we could reach our target depth with the lower completion complete with all redundant plans and contingency risks fully identified and in place.

Drilling MRC wells has continually pushed the technical limits of drilling equipment and technology with ADNOC leading the industry in their development. Prior to the development of MRC drilling, the conventional lower drain size selected for the field development was 6″. However, to reach ever growing drilling targets, the Drilling Team was successfully challenged to overcome technical limits of equipment, fluids, and drilling practice. From the best practices gained from other ADNOC concessions, the hole size to enable the highest drilling performance is 8-1/2″ in our reservoirs. This size allows the utilization of 5-1/2″ drill pipe over the 4″ which has mechanical limitations and was a blocker to develop drain lengths beyond 9,000ft. Wellbore trajectory control during drilling is also a critical component for the delivery of the MRC well and subject to large focus during the drilling phase. Over previous 6″ drain drilling, the acceptable DLS, standard tripping practices and hole conditioning requirements had evolved into a robust guideline that was applied to the 8-1/2″ drilling. The additional benefits of improved wellbore trajectory control and drilling ROP which contribute to the successful deployment of the Lower Completion. These high performance targets also require a high performance drilling fluid system with NAF fluids being successfully utilized.

The team's immediate challenge was to have confidence to run the 6-5/8″ lower completions in aqueous fluid that would deliver the same or similar friction coefficients to that of NAF. The capability of this greatly improves the subsequent efficiency of the well bore cleanout and mud displacement prior to running the lower completion. The immediate operational benefit is gained by eliminating approximately 5 days of rig time by not requiring an "inner string" clean-out after the lower completion installation.

For the planning of the two MRC pilot wells, it was agreed that a cautious approach should be taken with the Lower Completions to be deployed in NAF fluid to establish a base line for the friction factors. During the installation, the Offshore Team would conduct detailed condition monitoring and analysis of the operations, recording parameters both manually and real time. The same was done during the inner string displacement recording tripping parameters pre and post NAF displacement. The data gained was then extensively reviewed in drag analyzing computer software to identify if any significant change in the friction parameters between the NAF and aqueous fluid.

Our analysis confirmed that we had successfully achieved friction factors that would give us confidence to deploy the 6-5/8″ lower completion in aqueous fluid. In parallel we completed a detailed analysis with the Drilling, Completions and Fluids Teams where contingency plans were identified and put in place. In early 2021 the next MRC well was drilled where we had the opportunity to incorporate our learning. The lower completion was successfully installed in aqueous fluid with friction coefficients confirmed in alignment with those of NAF. Following this well and to date, the team has installed 20 further MRC Lower Completions in aqueous fluid, including the current record longest lower completion on Nasr at 17,616ft.

Benefits realized: Safety: Eliminating unnecessary tripping and reducing HSE risk exposure to personnel.Operational efficiency: Removing unnecessary cleaning trip saving 5 days per well (cost)Production efficiency: Efficient NAF displacement, enhanced preparation for stimulation program.Equipment: Eliminated the requirement for complexity with dissolving plugs, remote close shoes.Drilling Performance – Improved ROP, trajectory control and BHA reliability100X ADNOC Offshore: Continual improvement and operational excellence.