Last month the Washington University surgeons drilled a small burr hole, about the diameter of a pencil, into the patient's skull.
上个月华盛顿大学的外科医生用钻孔器在这个病人的头骨上钻了一个洞，直径大约和铅笔一样。
2
The original granite island which had hills up to 120 meters high was drilled and blasted into boulders no bigger than two meters in diameter.
原始的有120米高的花岗岩小岛被钻孔或是爆破直径成不大于两米的大石头。
3
Drilled formations are complex with unstable wall. Lost circulation, well kick, borehole collapse, diameter shrinkage, sticking and other complex situations often occur.