noise log

1. n. [Production Logging]
A record of the sound measured at different positions in the borehole. Since fluid turbulence generates sound, high noise amplitudes indicate locations of greater turbulence such as leaks, channels and perforations. Noise logging is used primarily for channel detection, but has also been used to measure flow rates, identify open perforations, detect sand production and locate gas-liquid interfaces. The log may be either a continuous record against depth or a series of stationary readings. The log may indicate the total signal over all frequencies, the signal at a single frequency, or consist of a set of logs for different frequency ranges. Different frequency ranges can be tied to different sources of noise or different flow regimes. Although first introduced around 1955, the technique was not used commercially until after laboratory studies in the early 1970s.