A Modified Archie Relationship for Vuggy Carbonates

Characterization of pore space properties is a fundamental problem in rock physics. Carbonates show diverse pore geometries and complicated pore structures (different scales and connections) resulting from their biogenic origin and diagenetic processes. Interparticle and vuggy pore space (separate or touching) are their two basic pore network types. Measurements of electrical resistivity, total and effective porosity were carried out on crystalline, weakly metamorphic and lagoonal carbonate samples. The investigations are intended to differentiate between intercrystalline and isolated vuggy porosity causing differences between total and effective porosity: The modified cementation exponent m’ was calculated with the equation of Schön (2011) accounting for the two pore systems. The vug porosity ratio (VPR), the ratio of non-connected to total porosity, was determined. Three ranges of VPR were chosen for a diagram presenting m’ vs. total porosity. The results show great potential in correlating VPR, m’ and total porosity with distinct carbonate facies. For instance, samples of facies types related to low water energy and restricted environments seem to be associated with a high VPR and m’, whereas higher water energy might be related to a lower VPR and m’.