The spatial organisation of deformation in high porosity sandstones: from outcrop data to prediction of bulk fault zone properties
Résumé
Understanding the evolution of fault zone geometrical and hydromechanical properties during fault growth and network development is of major importance in fluid flow prediction in the crust. In porous rocks, faulting produces zones of deformation bands rather than planar fracture surfaces. Cataclastic deformation bands (CDBs) are mm-cm thick brittle shear zones that form through the combined effects of compaction and cataclasis. Porosity and grain size reduction associated with CDB formation causes strain hardening, and the result is the initiation of a new band, adjacent to the first. Continued deformation may possibly result in the development of localised slip planes associated to DB zones. Plans for CO2 storage in porous sandstones must consider the role of deformation band-dominated faults in trapping or retarding the flow of CO2. Most commonly CDBs show a reduction of porosity, associated with a reduction of permeability. This permeability decrease is largest for the most evolved and thick zones of CDBs. Conversely, slip planes can potentially have a higher permeability than the host rock. Therefore CDBs in sandstone reservoirs can potentially retard fluid flow circulation and act as barriers to fluids, whereas slip planes could be conduits for flow. Previous studies have examined the effect of connected deformation band systems on flow, but have not considered the effect of "open" slip planes. To predict the effect of such structures on fluid flow we must consider the 3D connectivity of the relatively low permeability CDBs and
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