A highly sensitive, high-fidelity microphone employing a piezoelectric crystal that detects the disturbance caused by fluid movement downhole. Noise, or sound, is the disturbance created by mechanical energy moving through matter as a wave. A leak behind the casing where flow is constricted can create noise. Fluid moving through a hole in the casing can cause noise. The fluid movement in channels present in a cemented well interval can create noise. The use of a Noise Log can detect all these events.
The amplitude of the noise frequencies ranging from 200, 600, 1000, and 2000 hertz are measured. The noise log is often run in conjunction with a temperature log. They are primarily run in cased wells but can be used in fractured, hard rock environments exhibiting fluid movement from restricted fractures.
The side report represents a noise log detecting methane gas entering the well behind the casing at 1325 ft and 1410 ft.