侏罗系地层已钻穿。
在钻井施工中，白垩系、侏罗系地层井壁失稳严重。
In the drilling process, the collapse of wellbore wall is severe in the Cretaceous and Jurassic strata.
针对侏罗系地层高硬度、强研磨性等特点，研究并试验了几种特殊类型的钻头。
Considering the characteristics of high degree of hardness, abrasion and high temperature of Jurassic layer, some special bits were investigated and applied.
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