1. n. [Production Logging]

The change in direction of rotation that occurs when a spinner flowmeter tool is moving in the same direction, but faster, than the fluid. When the tool is stationary, moving against the fluid flow, or moving in the same direction but slower than the flow, it will rotate in one direction, perhaps clockwise. However, if it moves in the same direction, but faster than the fluid, it will rotate counterclockwise. This may happen at the bottom of a producing well, and, unless identified, can lead to a false interpretation.

See: effective velocity,  flow profile,  multipass method,  single-pass method,  spinner flowmeter,  threshold velocity,  two-pass method,  velocity correction factor