Fluid-Flow Properties of Early Faults in Sandstone Sequences

RDR research on fault rocks, recovered from within core from petroleum reservoirs shows that the faults or disaggregation zones formed under low mean effective stress in homogeneous clean sandstones (those containing <15% phyllosilicate material at the time of deformation) often have very similar microstructural characteristics and petrophysical properties to the surrounding host reservoirs and are unlikely to represent barriers or baffles to fluid flow. However, in some cases, with increased burial or in more heterolithic sandstone sequences, the flow resistance across these deformation features may increase. We described four situations where the early deformation of clean sand sediments can produce much lower porosity and permeability fault rocks than that of their associated host sandstones.