# How to Calculate the Deviation of Inclination & Azimuth

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Inclinational and azimuthal deviations are important figures in the oil drilling industry. Inclination and azimuth work collaboratively to create degrees for angles that are relative to the directions being dug into the ground. Inclinational deviation -- referred to as msID -- relates to vertical deviation while azimuthal deviation -- or msAD -- relates to horizontal deviation. Together these values work to tell oil diggers which direction to drill. Specifically, inclinational and azimuthal deviations are the differences between the actual and the preferred well bore angles.

## Inclinational Deviation

Find the inclination angle, in degrees, of the well bore. Use a survey downhole instrument that tells you the angle of inclination by forcing the survey instrument into the ground. Read the meter to find the angle. A completely vertical angle is given the degree 0 and a horizontal angle is assigned the degree 90.

Calculate the inclinational deviation. The inclinational deviation is the difference in the inclination between the planned well path and the actual well path. Since you already know the angle in degrees for the actual well path, you must find the angle in degrees of the planned well path. This information is found in the blueprints of the well bore. Use a protractor to measure the angle in degrees.

Subtract the actual well path inclination from the planned well path inclination to find the deviation in degrees. For instance, if the actual well path inclination is 92degrees and the planned well path inclination is horizontal, or 90 degrees, the inclinational deviation is 2

## Azimuthal Deviation

Find the azimuthal angle of the well bore, in degrees. The azimuthal is the horizontal version of the inclination angle. The inclination angle measures the vertical direction and the azimuthal angle examines the horizontal direction. This measurement is relative to north, east, south and west. That is, north-facing horizontal planes have a degree of 0, while South-facing horizontal planes have a degree of 180. East has a 90-degree assignment and west a 270-degree assignment.

Calculate the azimuthal deviation. This measurement is the difference between the actual and planned well paths. Review the blueprint plans and find the angle of the azimuthal horizontal plane using a protractor.

Subtract the actual from the planned azimuthal well paths to solve the equation for the azimuthal deviation.