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 8½Љ 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.

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Harsh rock applications in general, specifically carbonates, are challenging in many aspects: 1) A combination of rock ductility and high strength contributes to low rate of penetration (ROP) in carbonates. 2) Applications are generally interbedded. 3) Significant thermal degradation of the cutters, especially in the shoulder area of the PDC bits, costs companies premature bit wear and unwanted extra runs. This paper presents the development of a new drill bit technology that addresses those challenges. More than 40 pressurized laboratory experiments were conducted on Carthage limestone to identify proper positioning of a new shape cutter for carbonate applications. Furthermore, computational fluid dynamics (CFD) coupled with finite element analysis (FEA) were implemented to evaluate solutions to prolong the thermal life of the PDC cutters. This resulted in development of a novel nozzle geometry to cool and clean primary cutting structure as well a dedicated flow path for the secondary cutters. After successful laboratory testing, the new product and features were tested in several field applications in both North America and Middle East.

Ever evolving drilling performance requirements dictate bits drill wider ranges of lithologies while offering improved efficiency and reduced NPT. These performance requirements necessitate compatible drill bit technologies. As lithologies associated with these drilling objectives tend to be harder and more abrasive; the need for adaptable, durable, and efficient drill bit designs is intensified. With these challenging applications / objectives, Polycrystalline Diamond Compact (PDC) technologies are pushed to their material limits. These limits emerge as failures in PDC thermal fatigue, abrasion, and impact damage.Due to the absence of state-of-the-art drill bit material technologies compatible with achieving these drilling objectives, multiple trips are commonly required. Often, this translates into the use of non-PDC bits (Rolling Cutter and Impregnated) to complete challenging sections. As efficiency is hindered by bit type and increases in non-productivetime due to multiple bit trips, operators incur significant cost while drilling these intervals.New drill bit technology capable of drilling these lithologies and performance requirements is unmistakably needed. This paper describes the development of novel drill bit technology aimed at this requirement. This technology is born through the fusion of existing bit technologies; Fixed Cutter and Impregnated Diamond, and a unique design philosophy providing greater versatility in drilling a wider range of harsh lithologies, not typically drilled entirely with PDC bits. This novel design philosophy includes optimized cutter placement and exposure of diamond impregnated mix applied in critical areas of the bit.This project was initially targeted at the Sub-Saharan region in the Congo, where the existence of conglomeratic intervals still represents a challenge to reach TD in a single run for sections with high clonglomeratic percentage. In its first trial, the new technology hybrid bit drilled 300% more interval than the benchmark with 34% improvement in ROP, in comparable sections with similar conglomerate content. Subsequent runs have resulted in dramatic savings due to reduction of trips as well as improved ROP. This technology has provided the industry step change in performance and decrease in non-productive time.

When drilling in extreme environments, the integration of the latest advancements in materials engineering and cutter technology are crucial to maximizing drilling efficiency and reducing trips. Recent advances in hybrid bit technology have expanded the application range into lithology intervals that feature high compressive strength, high abrasivity and low drillability. By fusing existing technologies such as PDC and diamond impregnated cutting structures, designers have improved existing designs so they feature both optimized cutting element placement for extending bit durability and an engineered mix of diamond impregnated material strategically placed in critical wear-prone areas of the bit to increase exposure on hard and abrasive lithologies. These design changes also take into account the effects of a progressive combination of shearing and grinding rock failure mechanisms to maximize drilling efficiency.After initial applications in the Sub-Saharan region of the Congo, this bit technology has been featured in several applications across the world. These cases include runs onshore Jordan with highly interbedded lithologies; foothills area of Colombia drilling in rocks exceeding 25ksi UCS and offshore runs in Mexico within the middle and lower cretaceous areas with lithologies containing up to 10% Chert.In these case studies, the use of hybrid drill bit technology has reduced costs and NPT in situations where it would typically take a number of impregnated, PDC and tungsten carbide insert bits, many using different drive systems, to reach total depth. These cases also describe the different characteristics and drillability of the rock types, as each demands specific bit design features and parameters to be failed in the most effective manner.During the evolution of the hybrid design, the importance of PDC cutter selection played a crucial role in the design's success. Cutter technology was adapted to provide superior abrasion and thermal resistance, better suited to combat the high abrasivity of the formations. Additionally, the cutting edge geometry was modified to provide increased toughness, avoiding premature cutter edge overload to maximize the length of the bit run.