Physical properties and textural parameters of calcarenitic rocks: qualitative and quantitative evaluations

Petrophysical and mechanical properties of sedimentary rocks are influenced by size, shape, and packing of grains, porosity, cement and matrix content, all controlled strongly by depositional fabric and postdepositional processes. This paper presents a study on the textural characteristics of soft and porous calcarenites and the main methods to determine petrophysical data. The examined calcarenites, sampled from three quarry districts located in Apulia (southeastern Italy), are fine-grained and coarse-grained grainstones (“A” and “D”) and medium-grained packstones (“B”) belonging to a plio-pleistocenic formation (Calcarenite di Gravina) outcropping in the whole region. The study involved, particularly, textural analysis on thin sections using optical petrographic microscopy and evaluation of total and effective porosity by means of standard geotechnical laboratory tests, mercury intrusion porosimetry and image analysis. Grain size frequency distribution was also carried out by traditional sieve and sedimentation analysis on disaggregated materials and image analysis. Computer analysis of digital images was performed on photomicrographs applying the methods of quantitative stereology to pore size and grain size distributions. A comparison between results showed that each technique used has its limitations linked to the textural characteristics, primarily geometry and topology of the pore network, granulometry, grain shape and packing of calcarenites.