Complex Paleozoic Clastic Systems: Reducing Field Development Uncertainties with Quantitative Seismic Interpretation Workflows

Paleozoic clastic reservoirs in Central and Eastern Saudi Arabia are complex deposits and present a unique challenge in terms of field development cycles. The Unayzah Formation represents the youngest siliciclastic Paleozoic unit to be deposited before the regional transgression in the late Permian. In Central Arabia, the Unayzah Formation unconformably overlies Silurian rocks and ranges in thickness from 60 to 850 feet. (King, 1996) Standard quantitative seismic approaches in mapping the potential hydrocarbon-bearing layers have been addressed, initially by Melvin et.al. (2010), but are inadequate to fully understand the variations in reservoir fluid and mineralogy. To address this challenge, an integrated work flow was developed and is presented in this paper as a case study. A detailed core description was integrated with rock physics principals to first address the effect of fluid and varying mineralogy on the elastic properties. Secondly, the seismic data was reprocessed using Saudi Aramco proprietary algorithms for AVO inversion workflows. Rock physics models enveloping the field scale sedimentological framework were then used to transform the standard AVO inversion elastic properties’ into 3D lithofacies with associated probabilities. The results have proved to be encouraging in terms of providing a spatial understanding of the hydrocarbon-bearing clastic reservoir and also in reducing uncertainty in the placement of development wells.