Reservoir characterization of tight gas sand - Integration of lithofacies and petrophysical properties, subsurface, Saudi Arabia

The lithofacies heterogeneity, paleoenvironments, and complex paleogeography pose challenges to exploration and development of tight gas sand reservoirs in Saudi Arabia. This study aims to investigate the heterogeneity of the lithofacies and depositional environment of Sarah Formation and to evaluate their reservoir quality. Four lithofacies associations including bioturbated massive sandstone, grayish massive sandstone, diamictites, and partially deformed sandstone were identified and interpreted as nearshore, glaciolacustrine delta, subglacial tillite, and glaciofluvial outwash environments, respectively. The correlation and comparison between the lithofacies and the petrophysical data revealed that the glaciofluvial and the nearshore lithofacies at the western and the eastern margins of the basin have better reservoir characteristics than the glaciolacustrine delta and subglacial lithofacies located close to the basin center. The heterogeneity in permeability data within all the lithofacies is higher than that of porosity data. Both porosity and permeability are diminished by grains compaction, cementation and matrix content. Conversely, the reservoir proprieties are enhanced by natural fractures and feldspar dissolution producing sweet spots intervals. The evaluation of the Sarah Reservoir relies on the understanding of its lithofacies associations and its reservoir characteristics. This study provides leads for solving some of the challenges related to tight gas sand exploration and exploitation.