1. n. [Drilling]

A term to describe the inclination from vertical of a wellbore.

See: deviation survey,  inclination

2. vb. [Drilling]

To guarantee the inside diameter of a pipe or other cylindrical tool by pulling a cylinder or pipe (often called a rabbit) of known outside diameter through it. The drift diameter is the inside diameter (ID) that the pipe manufacturer guarantees per specifications. Note that the nominal inside diameter is not the same as the drift diameter but is always slightly larger. The drift diameter is used by the well planner to determine what size tools or casing strings can later be run through the casing, whereas the nominal inside diameter is used for fluid volume calculations such as mud circulating times and cement slurry placement calculations.

See: casing string,  inside diameter,  rabbit

3. vb. [Drilling]

To pass a gauge through casing, tubulars and completion components to ensure minimum-diameter specifications are within tolerance, as described in definition 2. This task is also performed to ensure that there is no junk, dried cement, dirt, rocks or other debris inside the pipe.

4. n. [Geophysics]

In calibration of a check-shot survey, the difference between geometrically corrected transit time and integrated sonic time.

See: check-shot survey,  transit time

5. n. [Geophysics]

A gradual change in a measurement or recording device during surveying. Reference to or repetition of a measurement at a base station can indicate whether drift is a problem.

See: base station,  survey

6. n. [Well Completions]

An accurately machined device that is pulled through the casing, tubulars and completion components to ensure minimum-diameter specifications are within tolerance, as described in definition 2. While this tool is usually of a short length, the well planner may specify a special drift that either has a longer length or a nonstandard outside diameter. The large-diameter casing drifts are frequently known as "rabbits."

Synonyms: rabbit