well slough 钻井过程中井壁失稳垮塌的现象。 发生井塌的原因包括：井内液柱压力不能平衡地层压力；地层受钻井液浸泡，发生水敏膨胀、破碎、剥离；地层本身破碎、疏松，上提钻具时造成抽汲现象使下部井筒压力下降；在起钻过程中，未及时回灌钻井液造成井内液柱压力下降；停钻时间过长，钻井液性能发生变化；在裸眼井段长时间、大排量循环等。井塌严重时会导致井眼情况复杂，引起井内事故。
钻井风险主要包括井漏风险、井塌风险、井涌风险、卡钻风险。
Drilling risks include the risk of lost circulation, well fall risk, the risk of Wells flow, and sticking risk.
该气田地层裂缝发育，钻井过程中井漏和井塌问题非常严重，钻井作业十分困难。
Very severe problems during drilling were circulation loss and borehole collapse because of formation fracture growing, and drilling operation was very difficult.
钻遇地层复杂，井壁稳定性差，井漏、井涌、井塌、缩径、卡钻等井下复杂情况频发；
Drilled formations are complex with unstable wall. Lost circulation, well kick, borehole collapse, diameter shrinkage, sticking and other complex situations often occur.
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