25th International Meeting on Organic Geochemistry IMOG 2011

P-310
Implications of source rock and oil geochemistry to the
understanding of the petroleum systems of the Northern Red
Sea
Jennifer Scott 1 , John Guthrie 2 , Steve Crews 2 , Graeme Gordon 1 , Niall McCormack 1 , Dean
Griffin 1 , Laura Lawton 1 , Andy Pepper 2
1 Hess, London, United Kingdom, 2 Hess Corporation, Houston, United States of America
The integration of data from onshore samples, basin
modelling, and oil and source rock geochemistry, has
resulted in a better understanding of the petroleum
systems of the Northern Red Sea (NRS), Egypt.
The primary source rock in the NRS is thought to be
the pre-rift Dakhla Formation. These Maastrichtian
marls and calcareous shales outcrop onshore on the
western rift shoulders of the NRS. They were
probably deposited as part of the southerly marine
transgression of the Neo-Tethys during the mid-late
Cretaceous. There is also a lesser contribution from
the syn-rift source rocks of the Miocene Rudeis
Formation. Onshore pre-rift samples were analysed to
quantify organic carbon content, hydrogen index, and
geochemical characteristics. From these results, it
appears that the Maastrichtian Dakhla Formation is a
rich oil-prone source rock, analogous and genetically
related to the prolific late Campanian - early
Maastrichtian Brown Limestone in the Gulf of Suez.
Saturate biomarkers from oil shows in offshore
cuttings from NRS were used to identify the relative
contributions from pre-rift and syn-rift source rocks.
Figure 1 shows that oils sourced from the pre-rift
Dakhla/Brown Limestone are characterised by low
oleanane and high C29 (hopane) indices, and
isotopically light δ13C values (depleted in 13C),
indicating a more carbonate-rich source rock.
Meanwhile syn-rift sourced oils have higher oleanane
and are isotopically heavier (enriched in 13C).
Offshore NRS oil shows can be typed to both syn-rift
and pre-rift source rocks, indicating that the Dakhla is
both present and mature in the offshore NRS.
By comparing the geochemical characteristics of the
pre-rift from the NRS to a large number of oil and
source rock samples from the Gulf of Suez, source
rock facies and thermal maturity variations within the
pre-rift can be identified. Regional thermal maturity
modelling calibrated to well temperature data and
biomarker thermal maturity parameters (Figure 2) of
reservoir oils has improved the evaluation of thermal
maturity variations. Biomarkers and carbon isotopes
have been used to distinguish facies variations within
the pre-rift, and a potential proximal-distal marine
facies trend within the Brown Limestone/Dakhla has
been identified. This work has allowed for a better
understanding of the environment of deposition of
these world-class source rocks.
Figure 1: Carbon isotope parameters of oils and
source rocks (SR) from the Gulf of Suez and Northern
Red Sea.
Figure 2: Sterane maturity parameters used to
assess the relative thermal maturity of oils and source
rocks from the Gulf of Suez and Northern Red Sea.
Thank you to Hess and Premier for permission to
publish this work.
443