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The Effect of Polygonal Faults on Petroleum Systems and Reservoir Quality – The Case Study of the Eastern Mediterranean Levant Basin

Abstract

Polygonal faults are exceptional structures that nucleate in fine-grained sediments. Even though their effect on petroleum systems is poorly known, it is believed that they greatly affect reservoir quality and fluid flow. Their unique preferential nucleation in incompetent rocks makes them markers for sand bodies. Usually, identifying sand bodies in a frontier basin prior to drilling is a daunting task full of uncertainty, hence the increased exploration risk in these areas. In this contribution, we integrate geophysical and structural techniques, such as displacement analysis, to evaluate the growth of faults, assess their effect on reservoir quality and directly map the sand distribution in the Levant Basin, which is an emerging frontier basin with world-class discoveries. The Eastern Mediterranean Levant Basin contains exceptional layer-bound NW-SE trending normal faults observed in the Oligo-Miocene units. These faults are believed to be compaction related making them a particular type of polygonal fault systems. Based on high quality 3D seismic data, we analysed the growth of these faults by interpreting displacement variation on fault planes. This technique allows apprehending the spatial and temporal evolution of faults. We complemented this step by computing attribute and thickness maps in order to track the sand provenance and assess the basin's geodynamic evolution. Results indicated that the evolution and growth of faults have been affected by strong mechanical stratigraphy in the Oligo-Miocene units, with nucleation of fault segments in incompetent units, while competent ones were barriers to fault propagation. This quantitative and qualitative analysis indicated that any variation in fault geometries is correlated with a lithological change. Thus, we were able to differentiate between units with coarser grains and finer grains and refine the stratigraphy of the basin. In consequence, we propose a new sand distribution model for the Oligo-Miocene unit in the Levant Basin, which has significantly reduced exploration risk prior to drilling. This contribution provides an effective structural technique that can be applied in any passive margin setting to investigate the effect of faults on reservoir quality and sand distribution. This can be of high importance during assessment of the basin's petroleum system in general, and reservoir quality in particular. Thus structural analysis is an essential tool to reduce uncertainties during exploration.