Low compressive strength of softtomedium formations. Such as soft shale, soft limestone, soft sandstone, hard and soft abrasive interbedded medium formation.
低抗压强度的软到中等地层,如中软页岩。中软石灰岩。中软砂岩。和软硬研磨性夹层的中等地层。
2
PDC bits have been used to drill the homogeneous formation from softtomedium-hard, but they are not suitable for drilling in gravel and multi-interbedded formation.