Breaking Boundaries in Well Design: A Sustainable, High-Performance Approach for UAE Unconventional Oil Exploratory Wells

Abstract

Efficient drilling and high‑quality formation evaluation remain central challenges in UAE field operator company unconventional exploration program, where shale‑dominated intervals exhibit low permeability, reactive mineralogy, and narrow operational margins. Historically, Water‑Based Mud (WBM) has been used in pilot wells to support high‑resolution imaging; however, recurring wellbore instability, tight‑hole behavior, and repeated conditioning trips frequently compromised drilling performance and logging reliability. This paper evaluates the transition to an Oil‑Based Mud (OBM) system designed to improve wellbore stability, drilling efficiency, and data acquisition quality in unconventional pilot and horizontal wells. Three pilot wells were drilled using OBM and benchmarked against offset WBM wells. The OBM program integrated fluid design with geomechanics‑driven mud‑weight selection, optimized hydraulics, and fit‑for‑purpose bottomhole assemblies. The use of rotary steerable systems (RSS) with PDC bits further reduced tortuosity and strengthened both drilling performance and logging conditions. Additionally, an ultrasonic imaging tool was deployed for the first time in field operator unconventional formations to assess its performance envelope under OBM and elevated mud weights. Results demonstrate that OBM delivered significantly improved borehole stability, minimized reaming and wiper trips, enhanced rate of penetration (ROP), and enabled predictable tripping and wireline conveyance. Well #1 and Well #2 achieved the lowest drilling and logging times in the campaign, with 55–60% reductions compared to WBM offsets, while maintaining high‑quality formation evaluation. Ultrasonic imaging under OBM at 12.5 ppg mud weight produced industry‑acceptable image quality, confirming its applicability within a defined operating window. Case studies further show that even high‑density WBM could not eliminate time‑dependent shale deterioration or wireline holdups, underscoring the operational and data‑quality limitations of WBM in this environment. This paper presents a sustainable well‑design methodology for unconventional exploration wells, integrating OBM, geomechanics, advanced BHA design, batch drilling practices, and a structured logging strategy. The approach ensures stable wellbores, efficient drilling, reliable conveyance, and high‑value subsurface data while reducing nonproductive time and operational risk. Recommendations are provided to guide future wells and support standardization of OBM‑based execution workflows.