A device for measuring in situ the velocity of fluid flow in a production or injection well based on the speed of rotation of an impeller, or spinner. The spinner can be helical, that is, longer than it is wide, or like a vane, which is similar to a fan blade. In both cases, the speed of rotation is measured and related to the effective velocity of the fluid. Friction and fluid viscosity cause the relationship to be slightly nonlinear at low effective velocities and introduce a threshold velocity below which the spinner does not turn. Results are interpreted using the multipass, two-pass or single-pass methods.

There are several types of spinner flowmeter. The most common device uses a small vane-like spinner, about 1. 5 in. (3. 8 cm) in diameter, allowing the logging tool to pass through the tubing and other restrictions before reaching the reservoir interval. The small spinner captures only part of the fluid flow in the casing, too little to make it turn in some low flow-rate wells and possibly unrepresentative in multiphase flow settings. Other devices have been designed to capture more of the flow, for example the fullbore spinner and various types of flow-concentrating or diverter spinners, such as the packer flowmeter and the basket flowmeter.