In the

oil 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 ...

, a deviation survey, or simply a ''survey'', is the measurement of 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 extraction of water ( drilled water well and tube well), other liquids (such as petro ...

's departure from the

vertical Vertical is a geometric term of location which may refer to: * Vertical direction, the direction aligned with the direction of the force of gravity, up or down * Vertical (angles), a pair of angles opposite each other, formed by two intersecting s ...

, expressed in

degree Degree may refer to: As a unit of measurement * Degree (angle), a unit of angle measurement ** Degree of geographical latitude ** Degree of geographical longitude * Degree symbol (°), a notation used in science, engineering, and mathematics ...

s (°). When a ''well plan'' dictates the drilling of a straight borehole, surveys are periodically taken to ensure that it will hit its target and also to ensure that it does not trespass underneath different property lines. These surveys can be taken fairly simply with a ''mechanical drift recorder'' more commonly known as a Totco or Totco barrel (named after the company that perfected the device). This device is run inside the

drill string A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid (via the mud pumps) and torque (via the kelly drive or top drive) to the Well drilling#Drill bits in mechanical drilling, drill bit. The term ...

attached to a wire on a wireline unit, down to the bottom of the drill pipe where the device (which is simply an inverted pendulum with a timer that punches a pin-hole onto a round paper tab delineated with concentric circles indicating increments of degrees) measures the angle of the hole and then is pulled back out to visually inspect to determine the angle. There are versions of this device that actually take a picture on film and are often used in situations where the

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematicall ...

(direction) needs to be determined also. When a ''well plan'' dictates a directional or horizontal borehole, more sophisticated tools are normally used. One such tool is the MWD (measurement while drilling) tool that uses electronic accelerometers and gyroscopes, to continually take surveys while drilling (as the name suggests) and also measures the

(direction). This tool is attached to the

itself and requires extra support personnel to use and interpret the data, and its costs are much more substantial. ( See well logging)

References

Petroleum engineering Oilfield terminology Drilling technology Field surveys {{Petroleum-stub

See also

References