oa Characterization of the Hercynian Unconformity, for Prospect Evaluation, Saudi Arabia

The Hercynian unconformity in the Arabian plate (Late Devonian to Early Carboniferous) impacts the<br>hydrocarbon resources and therefore is an essential aspect of prospect evaluation and field<br>development. We conducted a regional characterization of the unconformity using an integrated,<br>multidisciplinary method, including borehole images, dipmeters, open-hole logs, cores, seismic data,<br>VSP, inorganic geochemistry and palynology. The study included 13 key wells with over 14,000 ft of<br>borehole images (across the unconformity) and several hundred Km of seismic sections across key<br>prospects and traps.<br>The study shows the unconformity is manifested in distinct modes in terms of:<br>1. Unconformity facies: including conglomerate/breccia, paleosols, and disturbed zones due to soft<br>sediments deformation.<br>2. Angular discordance: including change in dip azimuth, or dip angle, or both.<br>3. Occurrence of tectonic faults.<br>The above aspects of unconformity modes offer different hydrocarbon configurations. These include<br>positive configurations that facilitate a sealing effect, potential reservoirs, or potential paths for<br>hydrocarbon migration. In addition they include negative configurations that result in losses of<br>potential resources, through weathering and erosion, of potential source rocks and reservoir rocks.<br>Case studies of these configurations from mainland Saudi Arabia are presented and discussed in this paper.