Field Results From the Noise-Logging Technique
Authors: Robinson W.S. 
Published: December 2007

Recent advancements in the noise-logging technique have made it a valuable tool for dealing with problem wells. This paper presents field examples where the noise log has been useful.

Introduction
An early attempt to establish a noise-logging system was made in 1955 by Enright. The noise-logging technique presented here was introduced to the oil industry in presented here was introduced to the oil industry in 1972. The down-hole tool and recording technique were developed by Exxon Production Research Co.; additional engineering by McCullough Services resulted in the present tool and surface equipment. present tool and surface equipment.The purpose of this paper is to present the logging results obtained during 1973. It is necessary to briefly review the principles of operation, current field equipment, and some laboratory data. Included in this paper are several examples of field results in different areas, with interpretation based on experience from various well conditions. A new surface panel has been built that results in faster recording in shallow wells and more data in deep wells.

Sound Energy
All sources of sound are in a state of vibration. Any composition of fluid flowing in a drilled well generates audible sound frequencies of 200 through 6,000 Hz. Sound energy radiating from these sources is transmitted through various well-geometry media and is absorbed by a transducer. The noise-logging tool detector is a unique transducer. When the energy from this vibrating motion is absorbed by a transducer, the mechanical vibrations produce electrical signals having an alternating-frequency produce electrical signals having an alternating-frequency wave form. The noise-log signal-wave form produced by the moving fluid is a composite of many frequencies, and the intensity of each frequency can vary with time. Selecting the proper time constant will give quantitative average values of the wave-form amplitude. The unit for this amplitude is alternating current (AC) millivolts.
Fig. 1 is an example of a noise spectrum from a laboratory test barrel in which a metered rate of air is bubbled into water as a sound source. The noise peak at 300 to 600 Hz is characteristic of two phases (gas through liquid flow), whereas the peak at 1,000 Hz is the result of single-phase flow (gas or liquid) across a pressure differential. Ref. 2 outlines a procedure for estimating leak rates from noise levels at the appropriate frequency.
There are five types of problems where the noise log has been useful:producing wells with cemented casing having channels or communication behind the casing;new wells with cemented casing, where channels develop before perforating for production or after squeeze jobs;drilling wells that develop underground crossflow or to check blowouts that have been stabilized;wells associated with an injection procedure; anddetermining relative flow rates from perforated zones.
A noise tool is sensitive to any flow that can be heard; therefore, the following considerations are necessary. The loud noise associated with wireline or down-hole tool movement make it compulsory to record all data during a time when the tool is stationary. All surface leaks must be eliminated in a "shut-in" well. Surface leaks include grease injector, wellhead connections, and especially wing valves.
JPT
P. 1370