High resolution saturated hydraulic conductivity logging of friable to poorly indurated borehole cores using air permeability measurements

Saturated hydraulic conductivity (Ks) is one of the most important parameters determining groundwater flow and contaminant transport in both unsaturated and saturated porous media. This paper investigates the hand-held air permeameter technique for high resolution hydraulic conductivity determination on borehole cores using a spatial resolution of ~0.05 m. We test the suitability of such air permeameter measurements on friable to poorly indurated sediments to improve the spatial prediction of classical laboratory based Ks measurements obtained at a much lower spatial resolution (~2 m). About 368 Ks measurements were made on ~350 m of borehole cores originating from the Campine basin, Northern Belgium, while ~5230 air permeability measurements were performed on the same cores. The heterogeneity in sediments, ranging from sand to clayey sand with distinct clay lenses, resulted in a Ks range of seven orders of magnitude. Cross-validation demonstrated that using air permeameter data as secondary variable and laboratory based Ks measurements as primary variable increased performance from R2 = 0.35 for ordinary kriging (laboratory Ks only) to R2 = 0.61 for co-kriging. Due to the large degree of small-scale variability detected by the air permeameter, the spatial granularity in the predicted laboratory Ks also increases drastically. The separate treatment of Kh and Kv revealed considerable anisotropy in certain lithostratigraphical units, while others where clearly isotropic at the sample scale. Air permeameter measurements on borehole cores provide a cost-effective way to improve spatial predictions of traditional laboratory based Ks.