Natural and laboratory compaction band in porous carbonates: a 3D characterization using synchrotron X-ray microtomography

Porous carbonates form important reservoirs for water and hydrocarbons. Post-depositional processes (e.g. mechanical) are important to quantify because they may affect the fluid flow properties of reservoirs. Field-based studies (Tondi et al., 2006; Rustichelli et al., 2012) described bed-parallel compaction bands (CBs) within carbonates with a wide range of porosities. These CBs are burial-related structures, which accommodate volumetric strain by grain rotation, grain translation, pore collapse and pressure solution. Cilona et al. (2012) performed triaxial compression experiments, under dry conditions on the porous cretaceous grainstones (the Orfento Formation, in Majella Mountain, Abruzzi), reproducing for the first time CBs in laboratory. In this work, the authors defined the pressure conditions at which natural CBs form and documented the role of Hertzian cracks for grain size and porosity reduction within the CBs. Here we use a new methodology to characterize the pore networks of natural and laboratory CBs and compare them with the host rock one. Data were collected using the synchrotron X-ray microtomography technique at the SYRMEP beamline of the Elettra-Sincrotrone Trieste Laboratory (Basovizza (Trieste), Italy). Quantitative analyses of the samples were carried out using the Pore3D software library (Brun et al., 2010). The porosity was calculated from segmented 3D images of deformed and pristine rocks. The process of skeletonization, which provides the number of connected pores within a rock volume, was applied. By analyzing the skeletons we were able to highlight the differences between natural and laboratory CBs, and to investigate how pore connectivity evolves as a function of the deformation. Preliminary results show that within compaction bands both pore volume and connectivity are reduced in comparison with the undeformed host rock. Natural CB has a lower porosity with respect to the laboratory one. In natural CBs, the contact among granules seem be welded, whereas in the laboratory CBs it shows pores with irregular shape.