Evolution and structural style of relay zones in layered limestone–shale sequences: insights from the Hammam Faraun Fault Block, Suez rift, Egypt

Abstract

A fully breached relay zone was investigated to gain insight into relay growth and breaching in layered limestone–shale sequences. Associated fracture patterns were analysed to gain a qualitative understanding of fault- and damage-zone evolution and fracture-related fluid conduits associated with fault overlap zones. Internally, the relay zone is characterized by dilatant brittle deformation in mechanically strong limestone of the stratigraphically upper part of the ramp, and down-dip shear along extensional detachments in stratigraphically lower and mechanically weak shale layers at the base. The linking damage zone is characterized by multi-directional fracture patterns, including fracture corridors at high angles to the main (bounding) faults. The causal relationship between fault growth and the complex fracture patterns lies in the interaction and progressive rotation of the local stress fields of overlapping or linking fault segments. Increasingly complex fracture patterns may therefore be expected during growth and linkage of fault segments. The observed fracture patterns, in concert with complex juxtaposition relations generated by dipping relay beds, indicate that fault linkage points in carbonate rocks represent localized conduits for cross-fault as well as vertical along-fault fluid flow. These have implications for hydrocarbon migration pathways and for reservoir connectivity during production from carbonate reservoirs.