Mega-Pressure Systems in the Arabian Basin

By

 Mohammed J. Al-Mahmoud¹, Abdulaziz S. Al-Guwaizani¹

(1) Saudi Aramco, Dhahran, Saudi Arabia

 The Arabian Basin is divided into three Mega-Pressure systems, based on detailed geologic and engineering data collected from oil and gas fields in Saudi Arabia. These pressure systems are named the Post-Jilh normally pressured system, the Pre-Jilh normally pressured system, and the Pre-Jilh over-pressured system. This work represents the first attempt to identify the pressure systems in the Arabian Basin.

The Post-Jilh normally pressured system extends from the Mesozoic outcrops in the west into the basin center at the Arabian Gulf in the east. The Pre-Jilh normally pressured system extends from the Paleozoic outcrops in the west to approximately mid-way between the outcrops and the Arabian Gulf. The Pre-Jilh over-pressured system occupies all areas to the east of the Pre-Jilh normally pressured system. Source rock studies and mud weight records suggest that the Jilh Dolomite separates the Post-Jilh system from the two Pre-Jilh systems throughout the whole basin. The Jilh Dolomite is an extensive 150-foot thick competent dolomite that is present near the top of the Triassic Jilh Formation. Deep sealing faults likely form the boundary between the two Pre-Jilh systems.

Smaller scale pressure systems are believed to exist within the three mega-pressure systems as indicated by the variations in pressures of the Permian Unayzah reservoir. A detailed mapping of such smaller systems and studying the causes of overpressures are necessary to understand the history of hydrocarbon migration and trap charging in the Arabian Basin.