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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.
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.
Historically polycrystalline diamond compact cutters have consisted of a planar cutting face on a cylindrical diamond table. For decades industry has been aware of the potential drilling performance gains from forming these cylindrical cutters into other geometrical shapes. These early generation shaped cutters did not gain traction due to limitations in diamond technology, and high manufacturing costs associated with shaping the cutters. Recently PDC drill bits with shaped cutter designs are becoming more prolific in worldwide drilling applications. Often, the novelty in the design of the cutter shapes is enticing enough to merit opportunities for field runs. However, without an informed understanding of shaped cutter behaviors, there is risk of diminished drilling performance if the cutter shapes are not applied properly to the bit and application. The objective of this paper is to develop methods to evaluate two critical behaviors for shaped PDC cutter designs, overload integrity and aggressivity, and apply these methods to a full bit drilling model. The cutter overload integrity characterization methods are developed using finite element analysis and the aggressivity characterization is based on high pressure visual single point cutter laboratory test data. The information is fed into a full bit drilling numerical model to predict bit performance and ability to avoid cutter breakage in a simulated drilling environment, accounting for factors such as lithology, interbedded transitions, bottom hole assembly type, and operating parameters. The models enable optimization of shaped cutter design and fit for purpose cutter selection. The full bit model is tested and validated against field runs. Case studies include interbedded drilling in the Haynesville and Permian Basins. In both applications, bits were run with different shaped cutter designs, using drilling performance and dull photos to compare to the model outputs. ROP gains of 35% were seen in the Haynesville application, while the cutter survival rate more than doubled in the Permian application by using optimally selected shaped cutters. The methods presented in this paper provide new pathways for shaped cutter design and selection. Digital tools are demonstrated to perform the multi-faceted analysis efficiently for pre-well planning and post-run analysis.
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.
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