Fast downhole fluid viscosity and density measurements using a self-oscillating tuning fork device

The ability to characterize fluids as they are being produced is of great importance for reservoir management in the petroleum industry. Real-time information about changes in flow characteristics and fluid composition during production requires downhole (or surface) measurements that are able to probe the properties of the fluid in time scales shorter than those of the characteristic flow speeds. In this work, we demonstrate the use of a tuning fork sensor for fast viscosity and density measurements which would enable the characterization of transient fluid properties such as in multiphase flows of liquids. This functionality is enabled by using a piezoelectric tuning fork as the frequency defining element in an oscillator circuit. The feedback loop in the oscillator circuit is continuously turned on and off to allow the tuning fork to ring up and ring down. By monitoring the frequency and the decay rate during ring-down, transient changes in density and viscosity can be obtained within milliseconds in liquids. The compact measurement scheme implemented here allows us to use the tuning fork as a flow detection and fluid characterization sensor in an untethered well-logging tool for rapid downhole well diagnostics.