Deformation bands in normal fault damage zones, Southwestern Sinai, Suez rift, Egypt

Abstract

The present study provides evidence that the NW-SE normal faults in Nubian Sandstone reservoirs (Malha and Naqus formations) are surrounded by damage zones in which the rocks are affected by cataclastic deformation bands and small scale faults. The paleostress analysis of the small faults indicates that σ3 has NE-SW direction while σ1 is sub-vertical. The thickness of the bands is ranging from 3 mm to 1 cm. The density and thickness of the bands increase toward the faults and decrease backward. The deformation bands form two prominent sets. The first set is running in the NW-SE direction parallel to the main faults and dip towards the northeast and southwest, i.e. synthetic and antithetic conjugate sets. The second set has NE-SW direction and dip mainly in the NW in the Malha Formation and in the SE in Naqus Formation. The two sets of deformation bands mutually crosscut each other, suggesting that both sets developed during the same deformation event. The deformation bands are planar features and occur singly or form braided clusters. The microscopic studies indicate that the host rock is mainly quartz arenite and composed of fine to very fine, well sorted quartz grains which weakly fractured and cemented by calcite. The microscopic studies of the bands indicate that they composed of strong grain crushing (cataclasis) and clay minerals. This composition is probably causes reduction of porosity and permeability within the deformation bands. The reservoir rocks in the damage zones of the normal faults are divided into polygonal areas by the deformation bands.