Growth Histroy and Gas Potential of the Saudi Arabian Petroleum Systems

By

 Mahdi Abu Ali¹, Abdul Mutaleb Al-Qahtani¹

(1) Aramco, Dhahran, Saudi Arabia

 Integration of structural growth history with basin modeling provided possible migration scenarios of the different hydrocarbon systems. Peak oil generation for the Paleozoic has started since the early Jurassic, and peak gas generation since the early Cretaceous. Gas generation for the Mesozoic, however, has commenced since the Eocene.

Silurian source rock maturity shows a progressive increase in gas generation north of Ghawar and in the Rub' Al Khali. Jurassic source rock maturity indicates oil potential in east Arabia and gas in the Rub' AI-Khali.

Jurassic isopach shows basin tilt to the west due to the accumulation of thicker sedimentary packages during the late Jurassic. Since the Tertiary, however, reversal tilting of the Arabian Plate to the east could have influenced gas migration.

Hercynian structures terminating growth at the Jurassic could have been filled with Paleozoic oil over the greater Ghawar area. Paleozoic gas from the south of Ghawar source area would have flushed oil up dip towards Central Arabia, confirming the existing hydrocarbon finds, and filled south and west of Ghawar with gas. Paleozoic gas from the more mature east of Ghawar source area would have filled north Ghawar with more mature gas. Gas maturity over Ghawar increases from south to north. Any oil filled structures over Ghawar could have been cracked to gas.

In contrast, structures continuing growth to the present would have a higher chance capturing the later migrating gas. Determining timing of both structural growth and gas and oil migration would, therefore, significantly reduce the exploration risk for gas in Saudi Arabia.