true vertical depth

{{Short description|Depth of a hole measured vertically down}}

{{Use mdy dates|date=February 2025}}

{{Dicdef|date=May 2023}}

Image:True vertical depth.jpg itself, and its length is called the measured depth.]]

True vertical depth,{{cite web |title=True vertical depth |url=http://www.glossary.oilfield.slb.com/Display.cfm?Term=true%20vertical%20depth |publisher=Schlumberger |access-date=7 June 2023 |archive-url=https://web.archive.org/web/20060113235510/http://www.glossary.oilfield.slb.com/Display.cfm?Term=true%20vertical%20depth |archive-date=January 13, 2006 |language=en}} abbreviated as TVD, is the measurement of a straight line perpendicularly downwards from a horizontal plane.

In the petroleum industry true vertical depth 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"{{Cite web|url=https://www.glossary.oilfield.slb.com/Terms/m/measured_depth.aspx|title=measured depth - Schlumberger Oilfield Glossary|website=www.glossary.oilfield.slb.com|access-date=2019-05-21}} 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.