Methodology and Array Technology for Finding and Describing Leaks in a Well
Authors: Carpenter Chris 
Published: February 2017

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 181497, “Methodology and Array Technology for Finding and Describing Leaks in a Well,” by Freeman Hill, Halliburton; Andy Bond, Caelus Energy Alaska; and Michael Biery, Srinivasan Jagannathan, Darren Walters, and Yinghui Lu, Halliburton, prepared for the 2016 SPE Annual Technical Conference and Exhibition, Dubai, 26–28 September. The paper has not been peer reviewed.

This paper presents a new technology and methods that can detect leak locations in a well and illustrate the flow profile of the leak. A substantial amount of time and effort can be expended in repairing leaks in wells, and these methods can reduce that time. The paper shows results and compares them to those of other techniques for a well that had been shut in as a result of a small leak.

Background

Noise tools have been used to detect the sound of leak flow to provide an estimated description on the basis of the magnitude of the noise and the frequency properties. Typically, these tools consisted of one hydrophone or receiver that was limited to frequency and information recorded. The majority of these tools provided stationary measurements that can reduce the optimum intercept of leak or leaks. Many new calculations have been performed that have improved these results; nonetheless, they can still be hampered by physical properties of sound conveyance through layers of hardware or changes in the structure of the well.

During the last few decades, advancements in passive acoustic devices have included broadening measurements, improving quality, and increasing the observed aspects of the measurements. Meanwhile, minimal advancements have been realized in the oil industry for leak/flow detection or characterization. The oil industry needed a device that could accurately locate and characterize leaks and flow behind pipe to reduce risks and nonproductive time. To improve the multiplicity of the sound measurement originating from fluid and gas movement, an array of hydrophone sensors was researched and tested to develop new relationships and characterization possibilities. The acoustic linear array with distributed hydrophone sensors could be synchronized to obtain information emanating from a flow source and fused together to obtain new insight into leaks and flow characterization. 

Localization by Use of an Array

One aspect of this new approach is based on a theory of beam forming in which multiple measurements or waveforms are used to localize the leak or flow in radial distance and vertical depth in the wellbore or surrounding region. Through beam forming, simultaneous estimates of vertical and radial location can be made of the sound source. This is achieved by calculating the time delay or phase shift between the sensors using a cross-correlation technique. Fig. 1 illustrates an acoustic source and array and shows how a basic beam-forming process functions under free-space conditions. 

Array processing and beam forming are performed using the frequency do-main in part based on spatial filtering algorithms. Beam-forming calculations create a 2D energy-distribution map over the area of interest. For the localization estimate, the radial and vertical components focus on the highest energy assessment. This method is used to determine real-time radial and vertical location while logging and in post-processing by use of high-definition data.