问答题 翻译：The casing and tubing used to bring crude oil to the surface is suspended underneath a wellhead or Christmas tree.

问答题 翻译：Other instruments used in gravity work are the torsion balance and the pendulum.These instruments, however, have been practically replaced by the gravimeter.

问答题 翻译：The permeability of a porous medium may be determined from samples extracted from the formation or by in-place testing.