针对以上难题，利用有限元法研究了钻柱在井底的二重非线性(几何非线性和接触非线性)问题。
Thus the finite element method is used to study the duplex nonlinearity (geometric nonlinearity and contact nonlinearity) of the drill string at the well bottom.
之后司钻上提整个钻柱，移去卡瓦，在开泵并旋转的同时小心地下放钻柱，当钻头接触到井底之后，重新开始钻进。
The driller then picks up the entire drillstring to remove the slips, carefully lowers the drillstring while starting the pumps and rotary, and resumes drilling when the bit touches bottom.
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