Effect of Permeability Anisotropy on Probe Permeameter Measurements

Probe permeameter (also known as Mini-permeameter) has been widely used in many field and laboratory applications where in-situ measurements and spatial distributions of permeability are needed. Mini-permeameter measurements have become popular techniques for collecting localized permeability measurements in both laboratory and field applications. It is designed to obtain fast, cheap, intensive and non-destructive permeability measurements and to describe the spatial arrangement of permeability. In this work, the effect of vertical and horizontal anisotropy on the probe permeameter measurements was investigated. A numerical simulation model for the rectangular system representing a porous rock sample was built based on finite difference discretization of steady-state flow of an incompressible single-phase fluid in a three-dimensional (3D) system. The seal and tip of the probe permeameter are represented by no-flow boundary and constant pressure boundary, respectively. All the sides of the sample are represented by a constant-pressure boundary in which the sample is exposed to the atmosphere. The investigation was conducted by examining different permeability anisotropy ratios. These include fully isotropic sample, different vertical anisotropy ratios in a horizontally-isotropic sample, different vertical anisotropy ratios at different horizontal anisotropy ratios. All these investigations are performed at a constant probe injection pressure of 50 psig at the injection tip. The results obtained showed the clear effect of anisotropy on the probe permeameter measurements and were expressed in dimensionless parameters. These dimensionless parameters include the ratio between the flow rate measurements at different directions for different vertical and horizontal anisotropy ratios. They also include the dimensionless pressure drop for the pressure drop measurements at different directions. From the plots of these dimensionless parameters, the permeability at different directions can be evaluated from a few steady-state flow rate and pressure drop measurements at different directions on a rectangular core sample. Therefore, a practical procedure for evaluating permeability anisotropy from probe permeameter measurements is also described.