Outcrop-Scale Variations in Petrophysical Properties of Faulted Carbonates: Exploring the Relative Influence of Lithology, Fault Displacement and Juxtaposition*

Carbonate reservoirs are highly heterogeneous in their internal fabric and structure, due in part to the variety of depositional and diagenetic processes that affect these rocks. This intrinsic heterogeneity presents major challenges when characterising the physical properties of a reservoir, either from seismic or well data. An additional factor in many regions is due to the effects of fractures. Variations in fracture patterns, or damage, around faults, provide an extra source of heterogeneity in fractured carbonate reservoirs. Fault damage zones are often the main conduits for fluid-flow, whereas fault cores tend to be sealing and act as barriers to across-fault flow. High strains in the fault core tend to obliterate depositional and diagenetic textures, which consequently have little influence on fluid flow. In contrast, lower strains in fault damage zones mean that the effects of depositional and diagenetic textures are more apparent. Porosity and permeability will be controlled by the combination of original textures and fracture patterns in the fault damage zone. This contribution explores the relative effects of original lithology, fault displacement and juxtaposition on the key petrophysical properties (porosity, permeability and seismic velocities) of faulted carbonate reservoirs based on outcrop analogues in Malta. Our eventual aim is to provide a quantitative understanding of: a) the ways in which extrinsic brittle damage around faults combines with intrinsic lithological variation of different carbonate facies, and b) how these combinations are expressed in the petrophysical attributes.