Conventional Core vs. Mini-Permeameter Permeability Measurements: Tensleep Formation

Conventional air horizontal permeability measurements collected at one foot sample intervals from the Tensleep Formation were compared to permeability values collected over the same depth range using a mini-permeameter with a sample frequency of 8 to 10 measurements per foot. The lithologies analyzed consisted of sandstone and dolostone from eolian dune, shoreface, sandflat, and shallow marine shelf facies. Comparison of mini-permeameter measurements averaged over one-foot intervals with the plug permeability value showed that the mini-permeameter average permeability value was higher in the shallow marine shelf and eolian lithologies. In the sandflat and shoreface lithologies, mini-permeameter values averaged over a one-foot interval were not significantly different from the single core plug permeability. Lithologies were analyzed by low power optical microscopy, thin section petrography, and scanning electron microscopy to characterize the pore system. The shallow marine shelf facies consists of dolomite with patchy sucrosic, vuggy, and fracture porosity. The average of the mini-permeameter measurements over a one-foot interval gave a better representation of all the pore system types observed. Eolian sandstones contain a matrix and fracture porosity system. The matrix porosity system shows variability in the size of pores and pore throats due to differential cementation by silica and dolomite and due to differences in grain size and sorting. Variability in the pore system is on a scale larger than a core plug in the eolian and shallow marine shelf facies which causes the deviation between the core plug and averaged mini-permeameter values. Shoreface units consist of homogeneously bioturbated fine-grained sandstone. The sandflat lithology is a ripple laminated fine-grained sandstone. In the shoreface and sandflat units, the pore system is largely uniform through the core on the scale of a core plug which causes no significant difference between core plug and averaged mini-permeameter values. The applicability of the mini-permeameter in providing a more detailed view of permeability distribution in a core is dependent on the uniformity of the pore system on a core scale.