25th International Meeting on Organic Geochemistry IMOG 2011

P-301
Biomarker distributions and δ13C values of individual n-alkanes
of source rocks, crude oils and oil components from reservoir
rocks of Tarim Basin, China
Changchun Pan 1 , Shuang Yu 1 , Jinji Wang 1 , Xiaodong Jin 1 , Lanlan Jiang 1 , Dayong Liu 1 ,
Xiuxiang Lü 2 , Jianzhong Qin 3 , Yixiong Qian 4 , Yong Ding 4 , Honghan Chen 5
1 State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of
Sciences, Guangzhou, China, 2 Basin & Reservoir Research Center, China University of Petroleum, Beijing,
China, 3 Wuxi Institute of Petroleum Geology, Sinopec, Wuxi, China, 4 Research Institute of Exploration and
Development, Northwest Oil Company, Sinopec, Urumqi, China, 5 Department of Petroleum Geology, Faculty
of Earth Resources, China University of Geosciences, Wuhan, China (corresponding
author:cpan@gig.ac.cn)
Numerous studies have been performed in oil
source correlation in Tarim Basin, however, the
origins of the discovered oils in the cratonic region of
this basin remain unresolved [1-3]. In the present
study, 54 oils and 70 oil-containing sandstones and
carbonates from the boreholes in the Tazhong Uplift
and the Tahe Oilfield in the Tabei Uplift, along with 24
source rocks within the Cambrian-Ordovician strata
from the boreholes of this Basin were analyzed using
GC-MS and GC-IRMS. Based on the ratios of
gammacerane/C31 hopanes and C28/(C27+C28+C29)
steranes, 3 of the 15 oils from the Tazhong Uplift
correlate with Cambrian-Lower Ordovician source
rocks while the other oils from the Tazhong Uplift and
all the 39 oils from the Tahe Oilfield correlate with
Middle-Upper Ordovician source rocks (Fig. 1a).
These two ratios further demonstrate that most of the
free oils and nearly all the adsorbed and inclusion oils
of oil-containing reservoir rocks from the Tazhong
Uplift correlate with Cambrian-Lower Ordovician
source rocks (Fig. 1b) while the free and inclusion oils
of the oil-containing carbonates from the Tahe Oilfield
correlate mainly with Middle-Upper Ordovician source
rocks (Fig. 1c). This result suggests that the crude oils
in the Tazhong Uplift are partly derived from
Cambrian-Lower Ordovician source rocks while those
in the Tahe Oilfield are overwhelmingly derived from
Middle-Upper Ordovician source rocks.
The δ 13 C values of individual n-alkanes are
relatively high for both the Cambrian-Lower
Ordovician and Middle-Upper Ordovician source
rocks, ranging (-32)−(-29)‰ (Fig. 1d) while relatively
low for the crude oils both from the Tazhong Uplift
and the Tahe Oilfield, ranging (-36)−(-32)‰ and (-
35)−(-33)‰, respectively (Fig. 1e). In addition, these
values are higher in the inclusion oils than free oils for
the oil-containing carbonates from the Tahe Oilfield
(Fig. 1f), implying that the initial charging oils are
heavier than the current in carbon isotopic
compositions of n-alkanes for these reservoirs.
Fig. 1 Crossplot of the ratios of C28/(C27+C28+C29) steranes
versus gammacerane/C31 hopanes (a-c) and theδ 13 C values
of individual n-alkanes (d-f) for the extracts of source rocks,
crude oils and the free, adsorbed and inclusion oils in the
reservoir rocks. In (a), (d) and (e), S1: the Cambrian-Lower
Ordovician source rocks; S2: the Middle-Upper Ordovician
source rocks; O1: oils from the Tazhong Uplift; O2: oils from
the Tahe Oilfield in the Tabei Uplift.
References
[1] Zhang, S. et al. (2000) Org. Geochem. 31, 273-
286.
[2] Sun, Y. et al. (2003) Org. Geochem. 34, 629-634.
[3] Pan, C., Liu, D. (2009) Org. Geochem. 40, 387-
399.
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