Percussion Drilling System Combined with Hybrid PDC Bit Increases ROP and Interval Drilled on Taoudenni Basin Well in Mauritania

Abstract

Abstract Drilling the Taoudenni Basin in Mauritania has posed a costly and time consuming challenge for operators looking to develop the basin economically. The formation's compressive strength limits the bit selection to heavyset PDC bits or hard rock roller cone insert bits due to their abrasive composition. One way to increase the effectiveness and drilling efficiency is to add a percussion force, increasing the axial energy, along with a hybrid PDC bit with PDC cutters and impregnated diamond material on the blades and secondary cutting structures. The main similarity between fixed cutter hybrid bits and roller cone bits is that both incorporate a similar means of energy transfer when used with a positive displacement motor. Axial weight from a drilling rig is applied while a hydraulic motor turns the bit at different speeds. A proposed improvement to this drilling system would be a new energy distribution system that induces axial oscillations and percussion force while still applying the same weight and torsional energy as previous systems. The system combines the torsional power of a conventional positive displacement motor with a high frequency axial pulse created by a mechanical action. The torque is still transferred directly to the bit and 100% of the hydraulic flow is utilized by the bit nozzles. The mechanical lifting and falling action creates a rapid variation in weight on bit (WOB), allowing the bit's depth of cut to fluctuate while overcoming different stresses. The percussion force created after each downward stroke, along with weight on bit variations, lead to increased rates of penetration (ROP). This system has already been utilized on two wells in Mauritania, drilling a variety of formations with PDC, hybrid fixed cutter and roller cone insert bits. This paper will focus on the 8½″ interval, drilling the Atar Group and Jbeliat Teniagouri formations. These formations consist of sandstone, shale interbedded with siltstone, dolerite and pyrite. Confined compressive strengths range from 20 to 30kpsi in top section to 60kpsi in lower intervals where dolerite appears. This new technology increased ROP by more than 52% and interval drilled by over 100% through these intervals.