True vertical depth
![](http://upload.wikimedia.org/wikipedia/commons/thumb/e/ec/True_vertical_depth.jpg/250px-True_vertical_depth.jpg)
True vertical depth[1] is the measurement of a straight line perpendicularly downwards from a horizontal plane.
In the petroleum industry, true vertical depth, abbreviated as TVD, is the measurement from the surface to the bottom of the borehole (or anywhere along its length) in a straight perpendicular line represented by line (a) in the image.
Line (b) is the actual borehole and its length would be considered the "measured depth"[2] in oil industry terminology. The TVD is always equal to or less than (≤) the measured depth. If one were to imagine line (b) to be a piece of string, and further were to imagine it being pulled straight down, one would observe it to be longer than line (a). This example oil well would be considered a directional well because it deviates from a straight vertical line.
See also
- Depth in a well
- Driller's depth
References
- v
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