Jin'gangshi yu moliao moju gongcheng (Oct 2024)
Mechanical properties and rock-breaking effects of ridge-shaped PDC teeth
Abstract
Objectives: With the depletion of easily recoverable oil reservoirs, the focus of oil and gas exploration and development in China has shifted to "two deeps and non-conventional" oil and gas fields. This transformation is not only accompanied by a significant increase in well depth and more complex formation challenges but also presents more stringent requirements for the design and construction of drilling engineering, which directly leads to a significant extension of the drilling cycle. The length of the drilling cycle is a key factor in determining drilling costs. Therefore, for a long time, scholars have been committed to improving the mechanical penetration rate and the durability of polycrystalline diamond composite (PDC) bits. The main purpose of this study is to analyze geological characteristics in depth, accurately match and optimize the design of special-shaped teeth in PDC drill bits, in order to significantly reduce the risk of drill bit failure and greatly improve mechanical drilling speed and footage. Given the wide application of PDC bits in hard rock drilling and their key impact on the cost and efficiency of drilling operations, this study focuses on the design and optimization of ridge-shaped PDC teeth, aiming to explore more suitable tooth structures for specific geological conditions through scientific testing and comparative analysis. This will promote innovation and efficiency improvements in drilling technology. Methods: Based on round teeth, the wear resistance, impact resistance, and rock-breaking effect of three types of ridge-shaped teeth were systematically tested. First, the wear resistance and impact resistance of three typical ridge-shaped PDC teeth—namely the 165 axe-shaped, 135 axe-shaped, and three-edged cutters—were tested to quantitatively evaluate their mechanical properties. Subsequently, granite was selected as the representative rock sample, and the single-tooth cutting tests were conducted with three different penetration depths to simulate the cutting effect under various drilling pressures during actual drilling. Additionally, a full-size bit simulation drilling test was designed to evaluate the drilling performance of each tooth shape under different pressures, and the data were compared with those of round teeth. This series of tests aimed to fully reveal the advantages and disadvantages of ridge-shaped PDC teeth in terms of wear resistance, impact resistance, and rock-breaking effectiveness. Results: The test results show that the three ridge-shaped PDC cutters significantly outperform the round teeth in terms of wear resistance. The 135 axe-shaped cutter, with the smallest ridge angle, exhibited the greatest improvement in wear resistance, indicating that the ridge design enhances the durability of PDC cutters and bits. In terms of impact resistance, the 165 axe-shaped cutter and the three-edged cutter performed excellently and could effectively withstand high impact loads, while the 135 axe-shaped cutter had relatively weaker impact resistance due to insufficient support at the impact point. Further analysis of the cutting force data revealed that the tangential force and normal forces of ridge-shaped cutters were lower than those of round cutters at the same cutting depth. The smaller the ridge angle, the smaller the cutting force, which indicates that the ridge design helps reduce cutting resistance and improve drilling efficiency. The full-size drill bit simulation drilling test results showed that the 135 axe-shaped cutter achieved the fastest mechanical drilling speed and is suitable for high-pressure operations. The three-edged cutter performed better in the low-pressure range (≤ 20 kN), while the round teeth had the slowest drilling speed and a lower suitable drilling pressure range. Additionally, the variation in ridge tooth angle not only affects the impact resistance but also directly influences the rock-breaking effect by altering the stress distribution within the rock. Conclusions: Through systematic testing and comparative analysis, this study has verified the significant advantages of ridge-shaped PDC cutters in improving drilling efficiency and reducing the risk of drill bit failure. Specifically, the ridge design effectively enhances the wear resistance and impact resistance of the drill bit while reducing cutting force and increasing mechanical drilling speed. The performance differences of the various ridge-shaped cutters under different drilling pressure conditions provide a scientific basis for the flexible selection of drill bit types based on formation conditions during drilling operations. In the future, further optimization of ridge-shaped PDC cutter designs, especially for specific formation conditions, will be an important direction for improving mechanical drilling speeds and reducing operational costs.
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