A detailed study of geometric factors for probe permeameter measurements on heterogeneous and anisotropic rocks

Probe permeameters are preferred for making fast, high density and non-destructive permeability measurements on relatively smooth rock surfaces. Probe measurements can be conducted with both steady-state and unsteady-state flows. The technique relies on geometric factors to account for the highly non-linear hemispherical flow, typical of probe measurements. Previous studies have presented geometric factors for homogeneous porous media.;Naturally occurring porous media are rarely homogeneous. Some heterogeneities are natural, others are created during drilling (formation damage) and some during subsequent core handling (slabbing). Unfortunately, our ability to deal analytically with heterogeneity is limited. Thus, it is necessary to use numerical methods to derive geometric factors for these complex, but realistic situations.;A finite element simulator was developed and used to study effects of fine scale heterogeneity and anisotropy on probe measurements and the difference between geometric factors for steady and unsteady state flows. 1-D experimental results for unsteady-state flow were simulated and flawlessly matched by numerical means. Experimental measurements and 2-D simulations were used to study the effects of a nearby flow barrier and a damaged zone on probe measurements. Flow barrier studies indicate that the effect of a local flow barrier is minimum when the barrier is located farther than half a probe-tip diameter from the measuring position. Results also indicate that measurements on damaged formations are profoundly affected by the damage zone thickness. A methodology was developed to obtain undamaged and damaged zone permeabilities, and damage thickness from three probe measurements.;We investigated the effects of anisotropy in cross-bedded formations by utilizing a tensorial representation of permeability. Several simulation runs were performed for different anisotropy ratios and considering different cross-bedding angles. Results are presented in the form of dimensionless parameters that can be used to determine principal directions of permeability. An iterative procedure was examined to determine the principal directions of permeability and concluded that few iterations were satisfactory for acceptable convergence.