Detailed diagenetic investigations of the lower cretaceous Yamama Formation, Riyadh, Saudi Arabia,

The evaluation of the diagenetic processes is essential in order to comprehend the heterogeneities of the carbonate reservoirs. Different diagenetic processes, especially the carbonate cements, have drastically changed the Yamama Formation, a large reservoir formation in the Saudi Arabian region. The current study aims to assess several calcite cements by using field, petrographic and geochemical analyses. Field studies from three outcrops show that the formation is thin to thick bedded limestone with small amount of shale and marl units. According to petrographic analyses, the cements are primarily composed of dolomite, blocky, drusy, granular, isopachous rim, and syntaxial overgrowth. According to the cathodoluminescence studies, diagenesis primarily occurred in a closed system with no major and trace element fluctuation or exchange. Carbon isotopic values show positive values (δ13C V-PDB = 0.23 ‰ to 3.19 ‰) falling within the range Cretaceous marine signatures suggesting no influence from the meteoric water. Oxygen isotope show negative values (δ18O V-PDB= -12.32 ‰ to -1.31 ‰) showing depletion from the Cretaceous marine seawater suggesting diagenetic alteration in different environments. Three stages of evolution—eogenetic, mesogenetic, and telogenetic—are included in the paragenetic sequence. Although their permeability is modest because of limited pore interconnectivity, intraparticle microporosity and intrafossil porosity have improved the overall quality of the reservoir.