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 should conserve evil just as we should conserve the forests. It is true that by thinning and clearing the forests the earth grew warmer.”
—Friedrich Nietzsche (1844–1900)
“I tell you, hopeless grief is passionless;
That only men incredulous of despair,
Half-taught in anguish, through the midnight air
Beat upward to God’s throne in loud access
Of shrieking and reproach. Full desertness,
In souls as countries, lieth silent-bare
Under the blanching, vertical eye-glare
Of the absolute Heavens.”
—Elizabeth Barrett Browning (1806–1861)
“Nature seems to have treasured up the depth of our mind talents and abilities that we are not aware of; it is the privilege of the passions alone to bring them to light, and to direct us sometimes to surer and more excellent aims than conscious effort could.”
—François, Duc De La Rochefoucauld (1613–1680)