Line (a) is an imaginary line representing the True vertical depth, while line (b) is the borehole itself, and it's length is called the measured depth
. True vertical depth is the measurement of a straight line Perpendicularly downwards from a Horizontal plane. A borehole is the generalised term for any narrow shaft drilled in the ground either vertically or horizontally Measured depth, as it is called in the oilfield, is the length of the Borehole, Line (b in the image and is measured in feet
A directional well[1], as it is known in the oilfield is any borehole that deviates from a vertically straight line. The petroleum industry includes the global processes of exploration, extraction, refining, transporting (often by Oil tankers and pipelines A borehole is the generalised term for any narrow shaft drilled in the ground either vertically or horizontally This is normally an intentional decision and done purposefully, to hit several target sands, for instance.