Pressure and Thermal Regimes and Systems in the Sedimentary Sequence of Central and Eastern Saudi Arabia

Abstract

Reservoir pressure data in central and eastern Saudi Arabia reveals the presence of two normally-pressured (NPR 1 and NPR 2) and two overpressured (OPR 1 and OPR 2) regimes. The NPR 1 comprises the sequence from the Saq through the lower Jilh Formations, from outcrops to 15,000 ft below ground. The NPR 2 comprises the sequence from the upper Jilh through the Dammam Formations and extends from outcrops to 14,000 ft. The OPR 1 comprises the sequence from the Saq through the Khuff Formations at depths from 12,000 to 19,000 ft. Overpressures in the OPR1 are a result of reduced porosity and permeability, and gas generation from the Qusaiba shale. The OPR 2 comprises the lower Jilh Formation at depths between 10,000 and 13,000 ft. Compaction and/or hydrocarbon charging from the Qusaiba shale could be the reason for overpressures in the OPR 2. The NPR 1, NPR 2, and OPR 1 are divided into pressure systems by stratigraphic seals, but these are locally breached by unconformities or faults forming local anomalies. Geothermal gradients illustrate shallow and deep thermal regimes (STR and DTR) separated by a high thermal conductivity zone (HTCZ). The STR extends from land surface to 8000 ft, with low and high gradients in the up-dip and down-dip areas, respectively. The DTR extends from 10,000 to 19,000 ft, with no differences in gradients between the up-dip and down-dip areas. The HTGZ lies between 8000 and 10,000 ft, with low gradients.