Laboratory investigation of acoustic behavior for flow from fracture to a well bore
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Copyright 2014, Society of Petroleum Engineers. Distributed acoustic sensing (DAS) technology is implemented to monitor downhole audible sounds for fracture diagnosis, leak detection and other applications. While DAS systems have the potential to enhance downhole flow monitoring, its use is currently limited to qualitative interpretation. Future applications of DAS such as distributed flow prediction require quantitative interpretation to determine flow rate, possibly of multiple phases, from acoustic data. In this paper we use signal processing techniques to determine flow rates from a simulated fractured well. Production into a 5 '/2-inch well is simulated by injecting fluid into a fracture. The fracture was originally simulated with a piece of pipe filled with proppant, and then we used a pair of proppant-filled parallel plates with dimensions of 0.2 inch wide, eight inch high, and sixteen inch long, to represent a fracture. Liquid and gas were injected at varying rates into the fracture and into the well. The noise from production was recorded with a hydrophone within the wellbore. Through signal processing, the sound signal collected is transformed into the Fourier domain for insight into the sound spectrum. Experimental results show that frequency and sound intensity varies with the flow condition. The acoustic signal is sensitive to the flow rate and the type of fluid. The peak frequency indicates the phase of the fluid and its magnitude indicates the flow rate. The frequencies for gas production are in a range distinct from those for liquid production and the sound levels are related to the flow rate for both fluids. Experimental results also show that fracture geometry has an effect on the sound that is generated and sound from production can be used to identify fractures with restricted widths.