Fracture Networks Development, Fluid Flow, and Diagenetic Processes in Sandstones and Carbonate Rocks

Sandstone and carbonate rocks form important geofluid reservoirs. Interaction therein among deformation and diagenesis is critical since both can deteriorate or enhance reservoir quality as well as affect its texture and mechanical properties. Deciphering their interaction is a critical prerequisite to the evaluation of the architecture, permeability structure, and mechanics of fault zones, the assessment of reservoir petrophysical properties uncertainties, and the understanding of the structural diagenesis evolution of rock volumes. We have made a comprehensive study of deformation bands (DBs) associated with calcite nodules in arkosic sandstone. We aim to elucidate how sandstone mineralogy control the deformation mechanisms, cataclasis intensity, and the band structure in arkosic sandstone; to quantify how DBs and nodules affect host rock petrophysical and mechanical properties; to characterize the subsurface network of sub-seismic structural and diagenetic heterogeneities (SDH); to assess the control of DBs on fluid flow and diagenesis. We have combined multiscalar mapping techniques, in situ measurements, microstructural observations, geochemical analyses, and modeling. We show that: cleavage-facilitated fracturing of feldspar results in (i) its preferential cataclasis with respect to quartz and (ii) cleavage control on cataclasis; DBs and nodules degrade porosity and permeability and strengthen the rock; DB, nodule, and the host sandstone have different GPR response that can be used to characterize the subsurface organization of SDH and variations in petrophysical and mechanical properties; DBs control flow patterns and this affects how diagenetic heterogeneities are distributed. We have also made a thorough study of the distribution heterogeneity of joints in a layered carbonate sequence, by means of field observations and 3D geomechanical modelling, to explain the occurrence and paleo-stress significance of joint clustering in chert nodules. We show that chert nodules in a deformed carbonate sequence can provide important clues on the paleo-stress conditions, the temporal sequence of events, and fracture distribution heterogeneity.