| 摘要 |
A method of drilling a borehole into an earth formation using a drill string having an upper part and a lower part which is more flexible than the upper part, the method involving drilling a first section of the borehole, drilling a second section of the borehole from the first borehole section, the second section extending at a selected inclination angle relative to the first section. During drilling of the second section the drill string is lowered through the borehole in a manner that the upper drill string part remains in the first section and the lower drill string part extends into the second borehole section.
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