The origin of oil in the Cretaceous succession from the South Pars Oil Layer of the Persian Gulf

The origin of the oil in Barremian–Hauterivian
and Albian age source rock samples from two oil wells
(SPO-2 and SPO-3) in the South Pars oil field has been
investigated by analyzing the quantity of total organic
carbon (TOC) and thermal maturity of organic matter
(OM). The source rocks were found in the interval
1,000–1,044 m for the Kazhdumi Formation (Albian) and
1,157–1,230 m for the Gadvan Formation (Barremian–
Hauterivian). Elemental analysis was carried out on 36
samples from the source rock candidates (Gadvan and
Kazhdumi formations) of the Cretaceous succession of the
South Pars Oil Layer (SPOL). This analysis indicated that
the OM of the Barremian–Hauterivian and Albian samples
in the SPOL was composed of kerogen Types II and II–III,
respectively. The average TOC of analyzed samples is less
than 1 wt%, suggesting that the Cretaceous source rocks
are poor hydrocarbon (HC) producers. Thermal maturity
and Ro values revealed that more than 90 % of oil samples
are immature. The source of the analyzed samples taken
from Gadvan and Kazhdumi formations most likely contained a content high in mixed plant and marine algal
OM deposited under oxic to suboxic bottom water conditions.
The Pristane/nC17 versus Phytane/nC18 diagram
showed Type II–III kerogen of mixture environments
for source rock samples from the SPOL. Burial history
modeling indicates that at the end of the Cretaceous time,
pre-Permian sediments remained immature in the Qatar
Arch. Therefore, lateral migration of HC from the nearby
Cretaceous source rock kitchens toward the north and south
of the Qatar Arch is the most probable origin for the
significant oils in the SPOL.