Goldschmidt 2012 Conference Abstracts
The Triassic lacustrine deposits in the
vicinity of maximum flooding surface
and oil black shales in Ordos basin,
China
YINYE WU1*, LUOFEI WU2 ,TING YUE3,TIANSHU ZHANG1
1Research Institute of Petroleum Exploration and Development, PetroChina，Beijing，China,
wyy@petrochina.com.cn
2 School of Earth and Space Sciences, Beijing University, Beijing , China, wlf_133@sina.com
3 China University of Mining and Technology,Beijing ,China, yueting200612@163.com
Background and methods
Ordos basin in China with Mesozoic lacustrine shale and siliciclastic
reservoirs have new oil discoveries in unconventional resources exploration
in recent years. The sedimentary microfacies and diagenetic phase of shales
and silstones are main factors influencing reservoir quality. A detailed
study on that domain will be efficient measures for predicting favorable
depositional belts and relatively higher quality oil shale belts and silty
permeable reservoirs on the background of low porosity and low
peameability.
There are 28 lines of outcrops studied and 200 photographs taken on
Ordos basin included Yanhe Triassic profile, Linyou-Chenshuihe Triassic
profile, Lonxian-Putuohe Triassic and Jurassic profile and Congxin-Nahe
Triassic profile and so on. Also there are 20 pieces of silstones and
sandstones sampled and made into thin section for observation.
In view of stacking pattern of parasequence and lacustrine area
changes, the Yanchan formation of late Triassic in Ordos basin went
through mainly three times of transgression and regression to lead to form
multiple deltaic sediments and three sets of source rocks and oil shales in
the vicinity of maximum flooding surface. In Yanhe Triassic profile, the
shallow lake shale of Chan 7 member can be interpreted as maximum
flooding surface, on which there develop mouth bar of deltaic front. Based
on above depositional evolution features, most siltstone and sandstones of
the fluvial-deltaic distributary channel with crossbedding are sediments
formed during early transgressive systems tract period or regressive
systems tract period[1].
In thin section observation, siltstones and sandstones from Yanhe
Triassic profile have a lot of laumontite cements appeared in the northern
and east-northern Ordos basin, originated from provenance full of volcanic
materials such as volcanic debris and ash and feldspar minerals. Sometimes
laumontite and calcite are appeared in the same visual field of thin section
that may imply multi-phase products. Therefore, the key to form high
quality reservoirs in Ordos basin is secondary pores of feldspar dissolution,
laumontite dissolution and calcite dissolution discovered in different area
of Ordos basin.
Conclusions
The distribution of oil shales are controlled by sedimentary facies
during trasgressive period, but siltstones and sandstones are influenced
mostly by diagenetic process. The main sedimentary environments of oil
black shales are shallow lake and moderately deep lake in the vicinity of
maximum flooding surface.
Key words：unconventional resources exploration , lcustrine facies, delta,
black shale, siliciclastic reservoir, Triassic, Ordos basin
*About the first author：Yinye Wu was born in 1964，and received his
PhD degree in petroleum geology from China University of
Petroleum(Beijing) in 1992. Now he is a research professor with his
research interests in sedimentology and petroleum geology.
[1] Catuneanu. (2009)Principles of Sequence Stratigraphy, 165-233.
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