1. n. [Production Logging]

In a gradiomanometer tool, the pressure difference observed when the fluid velocity opposite the upper pressure sensor differs from that across the lower pressure sensor. This difference usually occurs opposite points of fluid entry or exit, and at sudden changes in diameter, such as at the tubing shoe. The result is a sharp deflection on the log that may be misinterpreted as a local change in fluid density.

See related terms: fluid-density log,  friction effect,  holdup log