A vibrating plate fabricated by the methods of microelectromechanical systems (MEMS) for the simultaneous measurement of density and viscosity: Results for argon at temperatures between 323 and 423K at pressures up to 68 MPa

In the petroleum industry, measurements of the density and viscosity of petroleum reservoir fluids are required to determine the value of the produced fluid and the production strategy. Measurements of the density and viscosity of petroleum fluids require a transducer that can operate at reservoir conditions, and results with an uncertainty of about +/- 1% in density and +/- 10% in viscosity are needed to guide value and exploitation calculations with sufficient rigor. Necessarily, these specifications place robustness as a superior priority to accuracy for the design. A vibrating plate, with dimensions of the order of 1 mm and a mass of about 0.12 mg, clamped along one edge, has been fabricated, with the methods of Microelectromechanical (MEMS) technology, to provide measurements of both density and viscosity of fluids in which it is immersed. The resonance frequency (at pressure p = 0 is about 12 kHz) and quality factor (at p = 0 is about 2800) of the first order bending (flexural) mode of the plate are combined with semi-empirical working equations, coefficients obtained by calibration, and the mechanical properties of the plate to provide the density and viscosity of the fluid into which it is immersed. When the device was surrounded by argon at temperatures between 348 and 423 K and at pressures between 20 and 68 MPa, the density and viscosity were determined with an expanded (k = 2) uncertainty, including the calibration, of about +/- 0.35% and +/- 3%, respectively. These results, when compared with accepted correlations for argon reported in the literature, were found to lie within +/- 0.8% for density and less than +/- 5% for viscosity of literature values, which are within a reasonable multiple of the relative combined expanded (k = 2) uncertainty.