在非均匀水平地应力条件下，无论地层为各向同性或各向异性，套管应力均呈现非均匀分布态势，其套管应力极值变化不大。
When the horizontal in-situ stress is non-uniform, the casing stress is non-uniform at all times not only in the isotropic formation but also the orthotropic ones.
还有，下套管时，一定要慢，避免把地层蹩漏。
In addition, must be slowly while running the casing, prevent to make the formation lose circulation.
振动击打：用于松散的砂、卵石、碎石地层的钻进及下套管等。
C. Vibration strike: it is used in drilling and casing with loosen sand, cobble stone and gravel layer etc.
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