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:
“We can never safely exceed the actual facts in our narratives. Of pure invention, such as some suppose, there is no instance. To write a true work of fiction even is only to take leisure and liberty to describe some things more exactly as they are.”
—Henry David Thoreau (1817–1862)
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That only men incredulous of despair,
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Beat upward to God’s throne in loud access
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In souls as countries, lieth silent-bare
Under the blanching, vertical eye-glare
Of the absolute Heavens.”
—Elizabeth Barrett Browning (1806–1861)
“You are now
In London, that great sea, whose ebb and flow
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Vomits its wrecks, and still howls on for more.
Yet in its depth what treasures!”
—Percy Bysshe Shelley (1792–1822)