On the equivalence of measured and averaged pressures in porous media:

Fluid pressure in porous media is commonly measured by means of a manometer or a pressure transducer. The measurement is actually done on a body of fluids just outside the porous medium, which is in hydraulic contact with the fluid just inside the porous medium. It is almost always assumed that the measured pressure is equal to some volumetric average pressure of the fluid inside the porous medium. This major assumption however, has never been verified. In this work we discuss this issue. First for some simple single phase situations, we show that if there are pressure as well as porosity gradients in the porous medium, then the measured and the average pressures are not equal. Next we consider two-phase flow in a column where the two fluid pressures are measured using selective pressure transducers. Through numerical simulations of the porous medium and the transducers, we show that the measured and averaged pressures are distinctly different. We then share some ideas for a proper averaging of the fluid pressure. This work is closely related to the abstract submitted by Norbotten et al.Presenters: name: Berentsen, Cas affiliation: Utrecht University, Earth Sciences Department, Geohydrology grou