Fracture Patterns in Carbonate Fault Zones and their Influence on Petrophysical Properties

Maltese field examples of variable carbonate lithofacies in fault displacements ranging from ~20cm up to 100m are used to examine how different carbonates deform, and to understand evolution of the fault zone architecture and ultimately their petrophysical signatures. The evolution of fault zone architecture in time and space, and the associated changes in deformation mechanisms, exert an important control over the sealing potential of faults. It has been suggested that faults in carbonates could form seals after as little as ~20 m displacement, especially when juxtaposed next to a different formation. However, as seen in the Maltese examples, the complete opposite may occur. An intense zone of deformation is formed, which enhances both the porosity and permeability on an outcrop scale. This also prevents the localisation of deformation onto one slip surface, stopping the formation of a continuous, impermeable fault core. Examination of how the rocks deform, through different deformation mechanisms, can potentially help unravel the relationship between fault zone architecture and petrophysical properties. It can also help to indicate the potential evolution of the petrophysics through understanding scaling of the damage zone relationships with displacement of different carbonate lithofacies.