True vertical depth (TVD)

A true vertical depth is a depth vertically below a reference point to a point within a well.  It is the depth perpendicular to the Earth’s surface and is often referenced to sea level.  Wells are rarely drilled vertically but are deviated to a greater or lesser amount to some degree.  A depth indicated by pipe or wireline is actually a length that is not directly below the surface location.  It is calculated from knowing the continuous orientation of the borehole.


See also total depth and true stratigraphical thickness.



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