Cleaned Hydrophone Array Logging Data Aids Identification of Wellbore Leaks
Authors: Carpenter Chris 
Published: August 2022

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201512, “Enhanced Wellbore-Leak Localization With Estimation and Removal of Guided Wave Noise Using Array Hydrophone Logging Data,” by Yao Ge, Ruijia Wang, and Yi Yang Ang, Halliburton, et al. The paper has not been peer reviewed.
Leaks in wellbore tubulars emit acoustic waves in the borehole that can be captured by a hydrophone array. Processing the array data yields location and energy level of the wellbore leaks; however, the hydrophones also may capture other coherent noise propagating as guided waves along the borehole. The complete paper describes an approach to estimate and subsequently remove the guided-wave noise from the hydrophone array data to improve the accuracy of leak-source locations. Estimating the propagation direction and amplitude of leak-induced guided waves aids logging operations to locate a leak source efficiently.

Noise Logging and Well Integrity
Well integrity has become a focused area for most operators given the long life cycle and complex structure of a wellbore. Noise-logging tools have been developed to detect flow or leak in a wellbore. A typical noise-logging tool consists of one or two acoustic sensors logged through the depth of the well that produce the amplitude and frequency spectrum-log of the received acoustic signals.
A noise-logging tool usually operates in two modes—the continuous (or dynamic) mode and the stationary mode. In the continuous mode, the tool usually is logged through all accessible depths at a constant speed. Based on the data from the continuous pass, specific depths are identified and additional stationary mode passes are performed to stop the tool at selected depths and acquire higher-quality data. A major issue of the data from continuous logging is the presence of road noise, which is created by the centralizer, cable, or any part of the tool strings scratching against the casing or tubing. To reduce the effect of the road noise, a high-pass filter usually is applied to remove the signal from the lower-frequency range corresponding to the range of the road noise. However, this procedure could affect the quality of the leak signal when a portion of the leak signal lies in the lower-frequency range. The logging data taken when the tool is stationary for 1 minute or more at a target depth is free from road noise, but this approach prolongs logging time and limits depth resolution.
Aside from road noise, other forms of propagating noise exist in the wellbore, such as noise from surface or downhole equipment or propagating noise induced by a leak source. Road noise and all forms of propagating noises are referred to as guided-wave noise in the complete paper.
The guided waves usually propagate along the borehole’s axis for a long distance with low attenuation. However, traditional noise-logging tools with one or more omnidirectional hydrophones are unable to distinguish guided-wave noise from leak signals. Recent advances in noise-logging-tool design use array hydrophones to provide not only depth but also radial location of downhole leaks. The array hydrophones also enable an advanced array-processing method to measure and suppress the guided-wave noise.