Petrographic characterization of sedimentary rocks hosting deep saline aquifers suitables for CO2 geological storage

Abstract

Sedimentary basins are worthy to be studied because they contain the sedimentary record of processes on the Earth’s surface. Moreover they contain in their texture the tectonic evolution, fluid circulation effects and stratigraphyc history, important clues to understand in which way litosphere works (locally and regionally) and the final conditions of the sedimentary successions. This last point is one of the most critical boundary condition to perform numerical simulations for the investigation of the potential geochemical impact of CO2 in the reservoir host rock. The minero-petrographic characterization of the lithology of both the reservoir and the caprock is an important constrain for the development of a CO2 geological storage project. The possibility of trapping (solubility and mineral trapping) of the injected CO2 is strictly connected to the interactions beetwen carbon dioxide and rock formations via geochemical reaction in the fluid phases, one of the most challenging aspect is the evaluation of the caprock stability. In this paper are presented the petrographical investigations results of formations hosting suitable deep saline aquifers for CO2 geological storage. This work focuses on the assessment of major problems concerning i) the origin of the sedimentary rocks throughout the study of texture and fabric index, ii) the bulk rock modal mineralogical composition, iii) the burial history, iv) the evolution of sedimentary phases (silicoclastic, carbonaceous, chemical-biochemical or authigenic) during diagenesis (evolution of the constituents, characterization of the diagenetic reactions and study of the cements), and v) evidences of other geological processes inferring the depositional sequences (tectonic processes, evolution of the geothermal field, fluid circulations, mineralizations, etc.).