求翻译：PDC钻头在软到中等硬度地层中具有很好的破岩性能，机械钻速高，使用寿命长，钻井工作效率得到了大幅提升，综合经济效益显著，因而在钻井工程中得到了广泛应用。但是由于 PDC 钻头对于使用地层和工作条件敏感性强，在砾岩层及软硬交错等非均质地层中未能取得良好的使用效果，因此有必要针对砾岩层的地层性质，研究其主要失效形式和损坏机理以探索预防PDC钻头损坏，便于合理使用 PDC 钻头，进而提高其使用寿命。是什么意思？

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The PDC drill in soft to medium firmness layer is a very good performance in rock drilling speed mechanical high for long life, drilling productivity is significantly increased, with the overall economic efficiency, resulting in significant drilling engineering are widely used. But since the PDC bit

The PDC drill bit in softly has the very good broken crag performance to the medium degree of hardness stratum in, the machinery drills fast high, the service life is long, the well drilling working efficiency obtained the large promotion, the synthesis economic efficiency has been remarkable, thus

PDC bit in the soft to medium-hard stratum has a better breaking performance, high penetration rate, long service life, drilling work efficiency has been increased substantially, significant comprehensive economic benefits, which has been widely used in drilling. But because of the sensitivity of PD

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