True vertical depth 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 in oilfield terminology. The TVD is always equal to or less than (≤) the measured depth. If you imagine line (b) were a piece of string and pull it straight down, you would see that it would be longer than line (a). This example oilwell would be considered a directional well because it deviates from a straight vertical line.
Famous quotes containing the words true, vertical and/or depth:
“If it were true what in the end would be gained? Nothing but another truth. Is this such a mighty advantage? We have enough old truths still to digest, and even these we would be quite unable to endure if we did not sometimes flavor them with lies.”
—G.C. (Georg Christoph)
“In bourgeois society, the French and the industrial revolution transformed the authorization of political space. The political revolution put an end to the formalized hierarchy of the ancien regimé.... Concurrently, the industrial revolution subverted the social hierarchy upon which the old political space was based. It transformed the experience of society from one of vertical hierarchy to one of horizontal class stratification.”
—Donald M. Lowe, U.S. historian, educator. History of Bourgeois Perception, ch. 4, University of Chicago Press (1982)
“The lotus’ stem is as long as the depth of water,
So men’s height is just as great as their inner strength.”
—Tiruvalluvar (c. 5th century A.D.)