Nov 15, 2018 - 4Institute of Geosciences, Federal University of Rio de Janeiro, Brazil. Abstract ... Unlike the Sirte Basin no large oil or gas discoveries.
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Petroleum Geochemistry of the Qahash and Daryanah formations, Cyrenaica Basin, NE Libya Osama R. Shaltami1, Larsen Jorgensen2, Christian Elkjaer2, Fares F. Fares1, Hwedi Errishi3, Farag, M. EL Oshebi1 and Roberta Souza4 1
Department of Earth Sciences, Faculty of Science, Benghazi University 2
3
ExxonMobil, Irving, Texas, USA
Department of Geography, Faculty of Arts, Benghazi University, Libya 4
Institute of Geosciences, Federal University of Rio de Janeiro, Brazil
Abstract The main goal of the current work is the geochemical assessment of the source rock (Qahash Shale, Qahash Coal and Daryanah Shale) and reservoir (limestone and dolostone units of the Daryanah Formation) in the offshore well Al-NC 120, Cyrenaica Basin, NE Libya. Generally, the shales have a fair quality, whereas the coals are considered as a poor source rock. Moreover, the shales contain type II/III and III kerogen (mixed organic matter), while the coals are characterized by type IV kerogen (terrigenous organic matter). The organic matter is thermally immature. The Daryanah Reservoir is characterized by the predominance of immature oils. The biomarker ratios confirmed that the oils of the Daryanah Reservoir were sourced from the Qahash and Daryanah shales. In addition, these oils were charged at two different times. Keywords: Petroleum Geochemistry, Source Rock, Reservoir, Qahash Formation, Daryanah Formation, Cyrenaica Basin, Libya.
1. Introduction
there are four source rocks in the basin: 1) Early
Unlike the Sirte Basin no large oil or gas discoveries
Cretaceous shales (Qahash and Daryanah formations,
have been made in the Cyrenaica Basin (Hallett, 2016).
Hallett, 2016), 2) Late Cretaceous shales (Qasr Al Abid
This can be attributed to a variety of factors, but the
and Al Hilal formations, Buitrago et al., 2011), 3) Early-
most significant is the lack of an effective source rock.
Middle Eocene marls (Apollonia Formation, Shaltami et
None of the three main source rocks of Libya—the
al., 2018) and 4) Late Oligocene marls (Massah and
Tanezzuft hot shale,
the Frasnian shale or the
Qasr Al Balatah formations, Shaltami et al., 2018).
Cretaceous Sirte shale are present in the Cyrenaica
However, results are disappointing since no significant
Basin in a facies capable of generating significant
source rocks have been identified (Buitrago et al., 2011).
hydrocarbons (Buitrago et al., 2011; Hallett, 2016). According to Buitrago et al., (2011) three Cretaceous
The
Qahash
and
Daryanah
formations
were
and Tertiary reservoirs have been positively tested for oil
introduced by Duronio et al., (1991) for subsurface
and gas in the Cyrenaica Basin: 1) Early Cretaceous
sequences encountered in the Al-NC 120 and Al-NC 128
carbonates (Daryanah Formation), 2) Late Cretaceous
wells. The Qahash Formation contains rare non-
carbonates (Al Baniyah Formation) and 3) Middle-Late
diagnostic fossils, but on the basis of stratigraphic
Eocene carbonates (Darnah Formation). On other hand,
position it is believed to be Valanginian to Barremian in
4th Annual AAPG/ EAGE/ MGS Myanmar Oil & Gas Conference, Yangon, Myanmar, 2018
35
age, while the Daryanah Formation contains large
Geochemistry (LGQM), State University of Rio de Janeiro
foraminifera, gastropods, echinoderms and pelecypods
(UERJ), Brazil.
which indicate an Aptian-Albian age (Hallett, 2002). 3. Results and Discussion The present study aims to the following:
3.1. Evaluation of Source Rock
1) Re-evaluation of source rocks (Qahash Shale, Qahash
According to Buitrago et al., (2011) most of the
Coal and Daryanah Shale in the offshore well Al-NC 120
samples collected from the Qahash and Daryanah shales
(typical section, Figs. 1-2)).
from several wells in the Cyrenaica Basin contain fair
2) Assessment of oil of the Daryanah Reservoir
TOC contents (0.5-0.8%), and low S2 (
