Hydrocarbon Characterization
and Gas Potential of
the Saudi Arabian Mesozoic and Paleozoic Petroleum Systems
By
Mahdi Abu Ali1
(1) Aramco, Dhahran, Saudi Arabia
Saudi Arabia's Paleozoic and Mesozoic petroleum systems are discussed with respect to source rock generation potential and hydrocarbon geochemistry. Hydrocarbons found in both systems are extraordinarily distinct, suggesting the presence of an efficient seal separating the two systems. Carbon isotopes provided an excellent hydrocarbon-source rock correlation tool.
The Paleozoic petroleum system consists of the Early Silurian "hot" basal
Qusaiba shales as the principal source rock. The main reservoirs are the
Devonian and Permo-Carboniferous sands and carbonates
. The basal Khuff clastics
are the regional seal for the Permian Khuff and Unayzah reservoirs, and
interbedded shales for the Devonian Jauf
reservoir
. Hydrocarbons found in this
system include non-associated gas in Eastern Arabia and extra light oil in
Central Arabia.
The Mesozoic petroleum system is made up of the Jurassic and Cretaceous
sub-systems. Argillaceous carbonates
of the Tuwaiq Mountain and Hanifa
formations are the source rocks for the Jurassic system.
Carbonates
of the Arab,
Manifa, Hanifa, Hadriyah and Fadhili are the main reservoirs. The pervasive Hith
anhydrites are the major regional seal for the Jurassic system. Hydrocarbons
found in this system are typically medium to light oil and associated gas. The
Cretaceous system contains mainly two groups: light oil in the Shu'aiba
carbonate
reservoir
of the Shaybah field, and heavy to medium oil in the Wasia
clastic reservoirs of the offshore fields.
Based on basin modeling of the respective source rocks, Paleozoic hydrocarbon potential indicates gas in the east and south, and oil in Central Arabia, confirming the existing hydrocarbon finds. The Jurassic potential is oil for most of eastern Arabia and gas for southern Arabia. The potential for the Cretaceous section is mainly oil. Reconstruction of the basin's history along with hydrocarbon generation provided a regional interpretation of the oil and gas migration histories.