Distributed acoustic sensing (DAS) is an emerging technology in hydraulic fracture diagnosis. Current uses of DAS systems have been limited to qualitative analyses that pinpoint noise sources, such as injection into formation or production from a fracture. This locating of noise verifies that injection or production is happening and its sound intensities at the different stages give a relative indication as to which stages took more fluid or produced more fluid post-treatment.
In this paper we used signal processing techniques and quantitative analysis to measure flow rates in a simulated fractured well. Production into a 5-½ inch ID well was simulated by injecting fluid through a one-foot long packed bed of 16/30 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 or perforation tunnel.
Determining the fluid properties and flow rate can be achieved with DAS systems if the sound frequencies in addition to sound intensity are monitored. Incorporation of this technique into current DAS systems can give a real time value for injection rates during hydraulic fracture treatments and values for production rates from post treatment measure