ADNOC uses advanced fluid technology to drill longest onshore ERD well

Overview

Abu Dhabi National Oil Company (ADNOC) planned to drill an onshore extended reach (ERD) well to 32,000 ft MD, which would be the longest ERD to date in the UAE, with Halliburton as part of an Integrated Drilling Services project. The 8½-in. lateral section of 20,000 ft was thought to require two bit runs, as it presented challenges around hole cleaning, equivalent circulating density (ECD) management, and the risk of lost circulation. 

Challenge

This ERD well was more than 2.5 times the length of the longest offset onshore well previously drilled by ADNOC. Losses were expected while drilling the lateral section due to natural faulting in the area, and ECD control was needed to maintain a fracture gradient (FG) below 13.46 ppg. Other hurdles to overcome were low solids control efficiency, mud pump reliability, and top drive limitations of 130 rpm.  

Solution

Prior to this project, reservoir sections were drilled with water-based fluids but due to the longer lateral and associated higher friction factors, Halliburton Baroid recommended an invert emulsion system. The ADNOC Onshore operator expressed a preference to drill with a “diesel-based” invert emulsion fluid. The Baroid Technical Team, therefore, selected a 10.5 ppg organophilic, clay-free BaraXcel™ system with a calcium bromide internal phase to be used in conjunction with EZ-MUL® NT for optimum emulsification. The low-solids invert emulsion and fragile gel structure would minimize ECD and the risk of induced lost circulation while drilling or tripping. A bridging package consisting of sized BARACARB® materials was also proposed for sealing the formation and developing a thin, tight filter cake. The lower drill pipe rotation was a result of top-the-top drive limitations. Although this presented a hole cleaning concern, the tuned fluid rheology and high flow rates proved effective for in-hole cleaning. DFG drill-ahead hydraulics confirmed hole cleaning efficiency during both the pre-drill and execution phases of the well.

Results

Halliburton Baroid delivered a successful, record-breaking ERD well with above-average ROP compared to shorter offset wells drilled with water-based fluids. The section was drilled 10 days ahead of plan with rig time savings estimated at USD 350,000. The ECD values of the BaraXcel fluid system were maintained below the maximum FG, eliminating the risk of induced fractures and lost circulation. Seepage losses of only 10-20 BPH were experienced towards the end of the 20,000-ft interval.

The BaraXcel High-Performance Invert Emulsion with diesel-based fluid demonstrated stability while drilling the unusually long section, even under static wellbore conditions while tripping. Friction factors for the off-bottom torque were maintained below 0.18 while drilling the lateral section and 0.15 while tripping out of the well.

The BaraXcel system with accurate DFG hydraulics software simulations proved to be key success factors, causing ADNOC to consider these combined technologies for future ERD wells.