Acoustic Behavior of Multiphase Flow Conditions in a Vertical Well

Abstract

Operation and service companies in the oil and gas industry have recently deployed Distributed Acoustic Sensing (DAS) technology as a hydraulic fracturing diagnostic tool. However the uses of DAS technology are limited to qualitative analysis of sound generation along the wellbore by pinpointing the location and measuring the intensity of noise source. Increasing reservoir complexities require future DAS applications to be equipped with quantitative analysis of the fluid flow rate, multiphase fluid injection and flowing reservoir fluid properties from the acoustic data.

Signal processing technique is used in this paper to determine the flow rates from a simulated vertical fractured well. Reservoir fluid production is simulated by injecting liquid and gas through a 2 inch pipe into a 5 ½ inch diameter well. The noise produced is recorded by a hydrophone located at the perforation. The acoustic signal of sound is recorded in the time domain and is transformed into the frequency domain by Fast Fourier Transform (FFT) algorithm software to obtain the acoustic data for quantitative analysis.

The experimental results show that fluid flows into the wellbore through perforation produces different acoustic pressure magnitudes and sound frequencies. The fluids used for injection in this study are water and nitrogen gas. The peak frequency indicates the type of fluid injected and its magnitude indicates the flow rate. The sound frequencies of interest are distinct for different fluids as for liquid, it is in the hundreds Hz range and for gas, it is in the thousands Hz range. It is found that there is correlation between the acoustic pressures and the flow rate of both fluids. Acoustic pressure increases with the flow rate injected.