Hydrocarbon Systems of Central, Eastern and Southern Saudi Arabia
By
Abdelghayoum Ahmed1, Mahdi Abu Ali1, J. Michael Moldowan2
(1) Aramco, Dhahran, Saudi Arabia (2) Biomarker Technology, Sebastopol, CA
Hydrocarbons from Paleozoic and Mesozoic petroleum
systems are assessed with
respect to their source rocks potential and genetic relationships. Paleozoic
petroleum
system
source rocks principally include Early Silurian basal Qusaiba
hot shales. Mesozoic
petroleum
systems consist of Jurassic and Cretaceous
systems. Argillaceous carbonates of Tuwaiq/Hanifa formations are the principal
Upper Jurassic source rocks in eastern and southern Arabia. Middle to Upper
Jurassic source units are confined to northern Arabia area. Cretaceous source
system
comprises of Wasia formation in southern Arabia and both Wasia and Sulaiy
for offshore Arabia.
Paleozoic source rock potential indicates gas in the east and south, and oil
in central Arabia, confirming the existing hydrocarbon finds. Hydrocarbons found
in this system
include non-associated gas in eastern Arabia and extra light oil
in central Arabia. The Jurassic source potential is oil for most of eastern
Arabia and gas for southern Arabia. Hydrocarbons found in this
system
are medium
to light oil and associated gas. The source rock potential for the Cretaceous
section is mainly oil. Hydrocarbons include light oil in southern Arabia and
medium to light oil in the offshore areas.
Diamondoids, biomarkers and isotope data suggest that the Paleozoic oils are uncracked to lightly cracked in central area and southern Ghawar accumulations but are extensively cracked in north Ghawar field. In addition, some of the analyzed Paleozoic hydrocarbons show mixed origin as indicated by the presence of biomarkers and diamondoids. The possible hydrocarbon mixing from both Mesozoic and Paleozoic systems demonstrates migration complexity despite assumed effective seals.