**1. n. [Well Testing]**

The predominant flow geometry reflected in a pressure-transient response that is most easily recognized in the log-log presentation of the pressure-change derivative. The most easily recognized flow regime is radial flow, which produces a constant or flat derivative. Spherical flow, which may result from a limited-entry completion, has a characteristic -1/2 slope in the derivative. Wellbore storage starts as a unit slope in pressure change and then the derivative bends over in a characteristic hump shape. Linear flow produced by flow to a fracture or a long horizontal well has a derivative slope of +1/2. Bilinear flow results when the fracture has finite conductivity and has a derivative slope of +1/4.

**See:**
bilinear flow,
finite-conductivity fracture,
limited entry,
linear flow,
pressure transient well test,
spherical flow

**2. n. [Production Logging]**

A description of the geometrical distribution of a multiphase fluid moving through a pipe. Many different terms are used to describe this distribution, the distinction between each one being qualitative and somewhat arbitrary. In vertical or moderately deviated pipes, the most common flow regimes for gas-liquid mixtures are bubble flow, dispersed bubble flow, plug flow, slug flow, froth flow, mist flow, churn flow and annular flow. For oil-water mixtures, the most common regimes are bubble flow, slug flow and emulsion flow. In horizontal wells, there may be stratified or wavy stratified flow in addition to many of the regimes observed in vertical wells. Two-phase flow regimes have often been presented as plots, or maps, with the phase velocities or functions of them on each axis. Earlier maps were named after their authors, for example Griffith-Wallis, Duns-Ros and Taitel-Dukler.

**See:**
annular flow,
bubble flow,
churn flow,
dispersed bubble flow,
emulsion flow,
flow structure,
froth flow,
mist flow,
plug flow,
slug flow,
stratified flow,
Taylor bubbles,
two-phase flow

Flow regimes.