The role of detrital components in the petrophysical parameters of Paleogene calcareous-dominated hemipelagic deposits

The role of detrital components influencing the petrophysical parameters of calcareous rocks is primordial for understanding its effect on the porous space, which in turn control reservoir quality. Long (340 m) core encompassing Eocene carbonate sediments from the Negev area has been made available for conducting petrophysical analyses. The sequences investigated comprised the Paleocene to early Eocene age mainly composed of hemipelagic sediments of the Taqiye formation in the Negev, southern Israel. The sedimentary record separated into three zones (zones 1 to 3) based on variations in the lithology and petrophysical properties (density, magnetic susceptibility, and sonic velocity). The significant differences in the petrophysical parameters occur in lowermost zone 1 (Late Paleocene), which displayed erratic variations in measured sonic velocity, density, magnetic susceptibility, porosity, and insoluble residual contents higher than 10%. Zone 1 is primarily composed of intercalation of dark gray clay, hard white chalky limestone, and dark gray marl, with smectite as the dominant clay mineral. The overlying zones 2 and 3 (Early to Middle Eocene) are mainly composed of dark chalky limestone with some chert units, occasionally intercalated with gray chalky limestone. The petrophysical and lithological properties in these two zones gradually increase with depth according to a decreasing trend in porosity. The main factors influencing variations in the petrophysical parameters are the presence of clay content and carbonate dissolution. The depositional environment is predominantly composed of terrigenous sediments, and the deeper buried calcareous clay lithology derived from the overlaid sediments. The source of high magnetic susceptibility values observed in zone 1 is unclear. We have developed a useful empirical relation for the prediction of acoustic impedance in pure carbonate sediments. This study has produce, for the first time, critical high-resolution insights into the petrophysical properties of Eocene deposits from the northern Negev in southern Israel.