A Review of Vibrating Objects for the Measurement of Density and Viscosity in Oilfields Including Devices Fabricated by the Method of MEMS
William A. Wakeham, Alistair D. Fitt, Kelly A. Ronaldson and Anthony R.H. Goodwin
The thermophysical properties of fluids are required for the design of many industrial processes. In the case of design there is a choice to be made between prediction of the properties of the fluids from physically-based or empirical models and their direct measurement. For fluids and circumstances that is extreme it can be cost-effective to measure the properties directly with accuracy commensurate with the purpose. Process monitoring and thus control can be effective by continuous observation of a thermophysical property of a process stream. In either of these applications the instruments used for these in situ measurements must be able to withstand the conditions of measurement, and be robust and stable. Experience has demonstrated that these features can be provided for mechanical properties by the application of vibrating objects with a variety of geometries. In such instruments the complex resonance of a vibrating object immersed in a fluid is measured and then related to the required thermophysical properties using working equations founded on the principles of physics. In this paper we provide three examples of instruments that operate under these premises and yield data with an accuracy that are “fit-for-purpose”. These are: (1) a vibrating wire viscometer and measurements of the viscosity of diisodecyl phthalate (a fluid which could be used as a viscometer calibrant at viscosities of the order of 100 mPa·s); (2) the development of MEMS devices to measure both the density and viscosity of fluids with uncertainties of ±1% and ±10% respectively; and (3) a MEMS device to measure the non-Newtonian properties of fluids.