Step Change to Enhance Drilling Efficiency in Extended Reach Wells Using Under Reaming While Drilling, a Worldwide Record
Authors: Alzaki Hussien , Al-Sharafi Mohamed 
Published: February 2022

Abstract
Applying new technologies to improve existing methods or techniques can be important to successfully delivering high-profile ultra-extended-reach-drilling (ERD) projects. The underreaming-while-drilling technique in ERD projects represents such an opportunity. Recently, a 14½-in. borehole required being enlarged to 16 in. due to complexities, including surface location constraints, longer stepout, and borehole instability. This paper presents the challenges, how they were addressed, and the results.
A dynamic modeling system was used to model the planned drilling operation based on offset well data. The extensive engineering studies included a finite element analysis (FEA), which modeled the cutting interface designs for drilling rocks. This analysis emphasized the importance of the compatibility between the underreamer cutting structure and the drill bit, which can help to predict the drilling performance while eliminating costly trial-and-error field tests. The analysis also enhances drillstring dynamic behavior to diminish erratic torque while maintaining directional control. Taking on a challenging target dictated a multidisciplinary approach to achieve what was previously considered an impossibility.
The 14½-in. borehole was enlarged to 16-in. while landing at a 90° inclination successfully for the first time worldwide in an ultraERD profile. Several notable challenges were observed during the drilling phase, which required reevaluating the initially planned operations. A significant level of shocks and vibrations were observed, which required the bottomhole assembly (BHA) design to be further optimized in terms of bit cutting structure and string stabilization. The rate of penetration was optimized using real-time data from downhole drilling mechanics. The FEA results also allowed for developing an optimized drilling parameter plan for steering across the different formation horizons to be intercepted during the drilling operations. The mechanical specific energy was used as a monitoring tool to gauge drilling performance efficiency. Together with the mechanical specific energy, the plan for drilling parameters was adjusted in real time to deliver optimal BHA performance and ensure that no BHA vibrations, axial, torsional, and lateral, negatively impacted on the rock cutting process. Connection practices were also modified to account for pilot BHA length. The successful implementation of underreaming while drilling resulted in a significant savings in rig time, and subsequent cost savings equivalent to 20% to 30% of the section authorization for expenditure.
The potential benefits resulting from using existing enabling technology to further realize significant project savings exists. The application of underreaming while drilling is unique in the sense that the ERD requirements of the project are on the extreme scale of footage drilled and borehole size drilled horizontally. Lessons learned can be applied to similar projects to help shorten associated learning curves, improve project efficiencies, and ultimately ensure optimum delivery of high-quality, large, ERD wellbores.