As oil and gas wells become deeper, drilling longer intervals is becoming a major milestone for drill bit companies, as the process comes with a variety of challenges affecting the durability of drill bits. Among the major challenges are thermal and impact damage in polycrystalline diamond compact (PDC) cutters, which can significantly affect the performance and longevity of a drill bit. While cutter technology development remains an important arena to address said challenges, there exists a need to also address these through the design process. This paper presents the development and deployment of a new drill bit analysis method that addresses thermal damage by optimizing the design, which has been field validated across the globe. The analysis involves estimating the thermal input load and the available cooling rate for every cutter on a drill bit during drilling conditions. The data is then used to optimize and apply changes to the design. The analysis considers all the critical and relevant operational parameters to calculate these indices. The outcome of the so-called thermal index analysis enables the design team to make informed decisions to improve the design of the drill bit and to minimize the extent of thermal damage in cutters. The improvements made in the design include changes in cutting structure to affect cutting forces and, eventually, the thermal input load during the drilling process. This stage in practice can bring down the temperature of the cutting edge by 20%, as calculated analytically. Another major change that can affect the results is hydraulic design of the bit, which includes the location of the nozzles as well as their orientation and size. In test cases, the cooling rate improved by 50% while keeping the same flow rate though the bit. Several field trials have validated the correlation of thermal index analysis to drill bit dulls. This analysis is now in the field evaluation and testing phase, where it is being used during the design process to improve bits with thermal damage. The field-testing phase has been primarily conducted in thermally challenging applications across the Middle East, North Africa region, and in West Texas.
There are several challenges for polycrystalline diamond compact (PDC) drill bits when drilling through volcanic and interbedded applications. Roller cone (RC) bits have historically been used in geothermal applications. However, low rate of penetration (ROP), bearing life, and repairability limitations have halted progress in performance and economic gains. This paper presents game-changing PDC technology that addresses the limitations of previous conventional drill bits in a challenging geothermal application. A reimagining of drill bit body geometries, the latest in shaped cutter technology, and durable backup elements were lab tested and customized on an unconventional drill bit chassis to maximize ROP, improve durability, and reduce downhole torque variation. The initial design phase focused on identifying and overcoming these key challenges. The second phase was to field test the new drill bit in the target application and compare it to offset runs, including roller cone, hybrid, and conventional fixed cutter bits. Key performance indices such as ROP, durability, steerability torque generation/variation, and cost per meter (CPM) were considered when evaluating the new design's performance. Initial testing in the 16-in. section showed promising results in the field. Higher-than-average ROP and excellent interval resulted in the lowest cost per meter run. In addition, the drill bit complemented the bottomhole assembly (BHA) design well, as minimal effort was needed to keep the trajectory as planned. The delta torque generation was lower than conventional PDC bits whilst displaying higher ROP than roller cone alternatives. The improved durability of the new design also allowed it to be run multiple times without repair, which was not possible with previous bits due to bearing hours or durability issues. This was always a challenge through the volcanic formations seen in this application. In remote locations that do not have facilities to repair drill bits, the ability to run multiple times without the need to repair is critical. The operator saved costs by not needing to transport the bit and repair any PDC cutters or secondary components after multiple runs. This outstanding run validated the benefits of the new design in terms of both technical and economic perspectives.
Wellbore conditioning has become prominent in recent years as operators strive to reduce flat time costs. This paper examines how an eccentric wellbore conditioning tool (WCT) improves drilling performance and reduces flat time in challenging sections. Torque and drag are common challenges in extended laterals, with micro-doglegs and ledges being major culprits, especially in hard carbonate formations. The performance of the WCT is benchmarked in terms of flat time components: trip speed, system torque, rate of penetration (ROP), casing operations, and on-bottom performance. The paper also scrutinizes the allowable parameter envelope for wells drilled with and without the WCT. Laboratory testing was conducted to observe the behavior and effects of the eccentric WCT when confronted by the major wellbore conditioning challenges. Following these initial laboratory tests, a proprietary software program was created to determine the WCT's ideal bottom hole assembly (BHA) placement for field trials. Several field trials were conducted to validate the placement software's accuracy as well as the key benefits achieved by the WCT. Development testing has proven that the WCT's capabilities reliably improve wellbore quality and reduce overall torque and drag. Also, a proprietary software program confirmed the most effective WCT placement. Overall, there was a net flat time reduction and a marked improvement in ROP—up to 35% when directly compared with and without the WCT. Reduced system torque and less stress on downhole tools enable a wider and, more importantly, higher drilling parameter window. A new generation of eccentric WCTs has been introduced to solve a legacy drilling pain. Poor wellbore conditioning contributes to significant flat time costs for operators worldwide. A proven, effective solution has been long overdue; however, the WCT has shown to be a cost-effective tool, improving flat time and drilling performance. The benchmarking and exploration of drilling performance and reduced flat time provided by wellbore conditioning tools will allow others to exploit lessons learned and recapture drilling efficiency.
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