3D geometric evaluation of porosity types in carbonates

Abstract

In carbonate rocks, the complex shape of pore space results from an interplay of diagenetic processes and diversified rock fabrics. Therefore, only a 3D approach guarantees proper characterization of such pore systems. Moreover, large amount of data requires the introduction of a quantitative workflow, in order to capture small-scale geometric variations. To address this problem, this contribution focuses on finding the relationships between particular pore types and their numerically expressed characteristics. Zechstein Limestone (Permian) carbonate rocks, showing various pore types and skeletal grains were investigated. Three dimensional images with the resolution of 20 μm were obtained using X-ray microtomography. The digital images were processed and evaluated by means of the image analysis techniques. Particular pore types were assigned geometric parameters based on ellipsoid fitting, pore volume and surface area. Following pore types were recognized: (1) vuggy/interparticle porosity; (2) fractures and channels; (3) intercrystalline voids; (4) intraparticle voids and (5) mouldic porosity. The analyzed pore geometry varies between particular pore types. Additionally, the mouldic pores show significant bioclast shape inheritance, enabling their distinction from other pore types. Thus, it was demonstrated that X-ray microtomography is an efficient tool in pore type identification, specifically when dealing with samples containing numerous pores.