Fault Zones in Tight Carbonate Reservoirs: Outcrop Studies from the Suez Rift (Sinai, Egypt)

Bastesen, Eivind ¹; Rotevatn, Atle ¹
(1)Centre for Integrated Petroleum Research, University of Bergen, Bergen, Norway.

The current study takes aim to characterize and quantify fault zone attributes and properties that are critical for improving forecasting and modelling of structural reservoir heterogeneity in sub-surface carbonate reservoirs. We present detailed case studies of fault cores and damage zone properties from outcrops in Western Sinai, Egypt. Key parameters mapped include fault thickness, composition, geometry and displacement. In addition, the relationship between large scale structural features (faults) and subseismic structural damage (fault-related fracture systems) are addressed.

The present work studies natural exposures of faults in late Cretaceous to Eocene pre-rift carbonates in Suez Rift. This area, which comprises the eastern flank of the Oligocene-Miocene rift system, offers great exposures of extensional faults in fine-grained carbonates having undergone minor burial only. In order to gain a statistically valid dataset we have studied more than 100 extensional faults with displacements ranging from centimeter to kilometer scales. These faults display a wide range of geometries and compositions related to the variability of host carbonate sedimentology and a variable degree of fault-related diagenesis. Selected relevant cases from the outcrops studied are presented to shed to illustrate typical architectural and property characteristics of the core and damage zone of faults in tight carbonate reservoirs.

Variability in fault core composition appears to be controlled by host rock sedimentology/mineralogy, diagenesis and displacement. Variations in damage zone architecture appear to be controlled by mechanical stratigraphy, strain distribution and overall structural setting (e.g. fault propagation fold, rollover anticline, straight fault segment).

By constraining some or all of the above parameters using subsurface data (seismic and well data), the predictability of fault architecture and the distribution of subseismic structural features (fault related fracture patterns) may be improved. This in turn controls the hydrodynamic behavior of faults and thus may help improve production simulation and forecasting.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.