Characterization of the Hercynian Unconformity in Central and Eastern Saudi Arabia

Abstract

The Hercynian Unconformity has a profound influence on the petroleum system in the Paleozoic succession of Saudi Arabia. It controls hydrocarbon migration paths, entrapment, seal, and reservoir quality. An integrated multidisciplinary method has been developed in this study in order to diagnose and characterize the Hercynian Unconformity. The method includes the use of borehole data such as images logs, open-hole logs and core; seismic data; palynology and outcrop description. This method is considered to be a better approach to understand the unconformity than the previous studies. It covers a wider exposure compared to previous studies, and which focused only on open-hole logs, stratigraphic cross sections, isopach and isochron maps. The criteria employed in this study included the unconformity and its related facies, bedding angular discordance and palynology, for data obtained from the borehole data. It also involved study and analysis of truncation and onlap interpreted in seismic data. Strike, dip measurements and lithology description from the field data. The results obtained from this study indicate that the Hercynian Unconformity manifests itself in unconformity-related facies such as breccias and conglomerates, soft deformed sediments, and paleosols, all which indicate a period of nondeposition. Angular discordance in image logs is highly correlated with field data and is characterized by dip changes in both azimuth and magnitude. This indicates either structural tilting or faulting typically associated with unconformities. Seismic data reveals truncation and onlap, which are significant unconformity indicators.