ROP

The deep formation has a high degree of hardness and abrasivity;the bit type selection is difficult and the ROP is low especially under the high density mud.

深部井段地层的硬度高、研磨性强，钻头选型困难，特别是在高密度条件下机械钻速低。

Timely treatment of photocoagulation and (or) cryotherapy for prethreshold type 1 and threshold disease of ROP may lead to famous prognosis.

对阈值前病1型和阈值期ROP进行及时的激光和（或）冷冻治疗具有比较满意的疗效。