Can we ever predict how fluids may flow within and surrounding faults in carbonates?

A wide range of deformation and diagenetic mechanisms have been observed within faulted carbonate lithofacies.  These processes are known to influence the permeability of a fault, and hence the flow properties.  The mechanisms active during faulting are influenced by a range of factors, including: lithofacies, host porosity, host permeability, juxtaposition type, depth of burial, depth at time of faulting and kinematics.  Although we can estimate the fundamental controls on resulting fault rock permeability, the ability to predict flow properties within and surrounding faults in carbonates remains highly uncertain.  This presentation will discuss conditions for when a fault may act as a conduit or a potential barrier to flow, along with the gaps in current data and knowledge.

Further, conditions for when a permeability anisotropy may be created within the fault core of carbonate lithofacies will be presented, along with the implications for fluid migration across or along the slip surface.  A permeability anisotropy is observed within carbonate fault cores, dependent on lithofacies and juxtaposition.  The significant heterogeneity created when different lithofacies are juxtaposed outweighs the resulting permeability anisotropy that is created, such that no systematic permeability anisotropy can be defined.  However, when self- or similar juxtapositions occur, a systematic permeability anisotropy is recorded, creating a permeability that can be as much as over 5 orders of magnitude lower normal to fault strike than parallel to fault strike.  The permeability anisotropy is formed from differing mechanisms dependent on lithofacies; the intersections of shears with fractures/veins in recrystallised lithofacies, and oriented pores in high porosity grainstones.  This is similar to previous crystalline and siliciclastic studies.  The permeability anisotropy can act to allow flow in one orientation but prevent it in another.