Characteristics of Fault Zones in Layered Carbonate Sequences, Onshore Abu Dhabi, UAE

Abstract

Abstract The mechanical and kinematic properties as well as the structural architecture of fault zones are of great importance in structural geology, geomechanical modeling, and fluid flow studies. This paper emphasizes the structural/tectonic properties of the fault zones in the ADCO concession area. In general, fault zone properties are variable and are very hard to predict over short distances. It is impossible to extrapolate predictions of the structure of fault zones using seismic data alone given the resolution constrains. Therefore, this study serves as an attempt to incorporate and synthesize other data sources such as core and outcrop data to better characterize the fault zones of Abu Dhabi fields. In this study, data from available logs, cores, BHI (Borehole Images) and outcrop analogues were interpreted and integrated. Fault zone thickness variability has been observed in samples obtained from different faults of the same sequence and in samples collected at different positions along the same fault trace. The non-linearity of the fault zone thickness indicates the heterogeneous character of the fault zones, which in turn demonstrates the heterogeneity of the carbonate sequences. Fault zone permeability is also suggested to be as heterogeneous as the fault zone thickness. Interpretation carried out using outcrop data collected from Gebel Hafit and Ras Al Khaimah (United Arab Emirates) fault zones show that surface features such as natural drainages, changes in rock types, topography and other characteristics observed at the earth's surface are confined to fault zones. In the outcrops, fault gouge was affiliated with isoclinally folded and transposed bedding, rotated porphyroclasts and small-scale injection features that are attributed to ductile flow. In addition, the fault gouge displayed major thickness variations, which are also interpreted to be the products of ductile flow that occurred as a result of the slippage along fault planes. Within the fault zone, various geomorphic features are found that have their origin related to the lateral and vertical shuffling of fault-bounded slices and due to their presence near the master shearing fault. These features include offset, linear benches, aligned notches and saddles on spurs, scarps, fault-controlled drainage, and folds and pressure ridges. Understanding the mechanism in which fault- or shear-zone linkages' strength and microstructure evolve over fault deformation zones will ultimately lead to the development of more geologically realistic models of deformation that incorporate displacements which are concentrated in fault zones.