Distributed viscosity and flow velocity measurements using a fiber-optic shear stress sensor

The understanding and precise prediction of fluid and solid displacement is of great interest in many technical applications. Density and viscosity are two key parameters that govern process mechanisms. The possibility to measure transient processes over longer distances is desirable. We present a novel distributed shear stress sensor that allows to derive fluid rheological parameters such as the viscosity along a fiber-optic cable being exposed to a moving medium. This works because flow velocity and fluid viscosity directly translate to a shear stress and consequently to a tensile strain on the fiber optic cable. Using the technology of fiber-optic distributed strain sensing, strain changes (and temperatures) are detected in real-time at any location along the fiber. Given the cable mechanical properties and geometry of the flow path, the strain translates to a shear stress which can be correlated to either the flow velocity or fluid viscosity. We derive a theoretical characterization of the sensor based on the principles of fluid mechanics. Also, we perform laboratory experiments with the sensor and demonstrate that we can distinguish differences of 1 mPa s dynamic viscosities in a range as low as 1 - 7 mPa s. In the next phase, we are implementing this sensor into a real working environment in a wellbore application to investigate the applicability of this novel sensor technology.