Diagnosis of Fracture Flow Conditions with Acoustic Sensing
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Distributed acoustic sensing (DAS) is an emerging technology in hydraulic fracture diagnosis. Current uses of DAS systems have been limited to qualitative analysis that pinpoint noise sources, such as injection into formation or production from a fracture. Identification of noise verifies that injection or production is happening and its sound intensities at the different locations give a relative indication as to which locations took more fluid or produced more fluid post-treatment. Signal processing techniques and quantitative analysis are used to measure flow rates in a simulated fractured well. Production into a 5-? inch OD well was simulated by injecting fluid through packed bed of 16/30 mesh, 20/40 mesh and 30/50 mesh proppant. Gas was injected at varying rates into the fracture and into the well. The noise produced from production was recorded with a hydrophone. The acoustic signal was transformed from the time domain to the frequency domain through a fast Fourier transform (FFT) for analysis. The experimental results showed that the frequency of sound and its intensity were crucial in determining the amount of fluid being produced. The sound level of the peak frequencies were found to be linearly related to the flow rate. The results verified that sound alone can be used to measure flow rate through a proppant packed fracture and perforation tunnel. Incorporation of this technique into current DAS systems can give a real time value for injection rates during hydraulic fracture treatments and for production rates from post treatment measurements.