Velocity measurements in natural porous rocks

Abstract

In the petroleum industry, there is a general belief that there must be a correlation between porosity and permeability in oilfield cores. This has been demonstrated using porosity and permeability values measured on large cores from the same oil field. Now, with MRI techniques for non-invasively measuring fluid flow velocities and porosities inside oil cores, it is possible to develop quantitative correlations between local porosity and fluid flow velocity inside single core samples. Since velocity and permeability are related, these results could eventually be extended to give empirical equations relating porosity and permeability within a particular core sample. MRI was used to obtain local values of the porosity and fluid flow velocity in Casper sandstone during water injection. The correlation between local fluid velocity and local porosity is shown graphically and indicates that the average velocity increases with porosity, with no velocity for porosity equal to zero, as expected. In addition, the average flow rate of the fluid through the cross-section, as measured by MRI, is calculated and compared to the actual flow rate through the core sample. The results indicate bypassing of fluid around the perimeter of the core, and this conclusion is supported by 1D projections of the flow velocities at different overburden pressures.