True vertical depth'
is the measurement of a straight line
perpendicular
In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It can ...
ly downwards from a
horizontal plane
In astronomy, geography, and related sciences and contexts, a '' direction'' or ''plane'' passing by a given point is said to be vertical if it contains the local gravity direction at that point.
Conversely, a direction or plane is said to be hor ...
.
In the
petroleum industry
The petroleum industry, also known as the oil industry or the oil patch, includes the global processes of exploration, extraction, refining, transportation (often by oil tankers and pipelines), and marketing of petroleum products. The larges ...
, true vertical depth, abbreviated as TVD, is the measurement from the surface to the bottom of the
borehole
A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water ( drilled water well and tube well), other liquids (such as petro ...
(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 oil industry 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
oil well
An oil well is a drillhole boring in Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas may ...
would be considered a
directional well
A directional well is an oil industry term for an oil well with a borehole
A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extrac ...
because it deviates from a straight vertical line.
See also
*
Depth in a well In the oil and gas industry, depth in a well is the measurement, for any point in that well, of the distance between a reference point or elevation, and that point. It is the most common method of reference for locations in the well, and therefore, ...
*
Driller's depth
The original depth recorded while drilling an oil or gas well is known as the driller's depth.
The problem
Since there is not a single reference or measurement system for calculating the depth in sub-surface environments, two engineers talking ...
References
Oilfield terminology
Petroleum geology
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