Online Journal for E&P Geoscientists

Yassin, Mohamed A.^*1; Abdullatif, Osman M.¹; Al Ramadan, Khalid ¹
(1) Earth Sciences, KFUPM, Dhahran, Saudi Arabia.

This study investigates the lithofacies, depositional and diagenetic characteristics and heterogeneities and examines their impacts on reservoir properties of the carbonate and siliciclastic rocks of Dam and Hofuf Formations in eastern Saudi Arabia. The mixed carbonate-siliciclastic succession represents important reservoirs in the Mesozoic and Tertiary stratigraphic succession in the Arabian Plate. This study integrates field work and laboratory data including petrograaphic thin section, SEM, stable isotopes and petrophysical measurements. The Dam Formation is characterized by very high percentage of grain- dominated textures representing high to Low energy intertidal deposits a mixed of carbonate and siliciclastic succession. The middle Miocene Dam section is dominated by intra-clasts, ooids and peloids grainstones. The Dam Formation deposition followed by a slight marine transgression over an eroded Palaeogene surface during the Middle Miocene and the fluctuations of sea level (transgressive-regressive) led to the development of coarsening-upwards cycles (shallowing- upwards). The calcareous trough cross-bedded laterally accreted quartz sandstones represent an enstuarine deposits. The interbedded thin marl and quartz sandstones are interpreted as tidal flat deposits. The presence of stromatolites with peloids and ooids grainstones are interpreted as lower intertidal facies deposited during the early transgressive period. During the Miocene and Pliocene, the drainage from the Arabian Shield which uplifted by the Red Sea rifting, led to the deposition of vast amounts of sand-dominated siliciclastic sediments of Hofuf Formation. The Hofuf Formation represents fluvial to shallow-marine facies. The fluvial facies is characterized by mudclast-rich erosive bases overlain by pebbly conglomerates which pass upward into medium to very coarse grained massive, horizontally stratified and trough cross-stratified sandstone facies. The overbank fines mudstone facies makes minor proportion within Hofuf Formation. The porosity and permeability patterns show variability and indicates the influence of both depositional and diagentic controls. Understanding these controls at reservoir-equivalent outcrops is essential for the prediction of reservoir quality and architecture of the carbonate-siliciclastic successions in the subsurface.