25th International Meeting on Organic Geochemistry IMOG 2011

P-096
Analysis on hydrocarbon accumulation and key controlling
factors of oil & gas accumulation in the Qaidam Basin, NW
China
Shihu Fang 1,2 , Mengjun Zhao 1,2 , Shuichang Zhang 2 , Dade Ma 3 , Yongshu Zhang 3 , Yan
Chen 3
1 Key Laboratory of Basin Structure and Petroleum Accumulation, CNPC, Beijing, China, 2 Research Institute
of Petroleum Exploration and Development, Petrochina, Beijing, China, 3 Qinghai Oilfield Company,
Petrochina, Dunhuang, China (corresponding author:shfang@petrochina.com.cn)
The three tectonic events and uplift around the
Qaidam basin and peripheral areas were mostly
related to the tectonisms during the middle-late
Himalayan Period, due to the distant influence of the
India-Tibet collision. The hydrocarbon generation,
migration and accumulation in Qaidam basin were
controlled by these tectonisms, as showed in the
influences of tectonic events on evolution of source
rock, formation of trap and reservoir-cap rock play,
fault system, and stages of hydrocarbon charging. All
the controlling factors led to differential distribution of
oil and gas in the Qaidam badin.
As study proved, there developed two-type of
accumulation models in the western Qaidam basin,
formed by the combination between the two stages of
hydrocarbon accumulation in this area. One is the
accumulation during the last stage of N2 1 or combined
with that during N2 3 -Q in the south part of western
Qaidam, and the other is that accumulating during
N2 3 -Q in the north part of western Qaidam. The twotype
of accumulation models can be subdivided into
four types. The structural formation during the late
Himalayan Period and its relationship with critical
period of accumulation led to differences in
hydrocarbon accumulation and related key controlling
factors. The differential response of late tectonic
events, major source rock evolution and fault system
are the three key factors that led to the obvious
differences of reservoir forming characteristics and
models between the north part and south part of the
western Qaidam. The role of fault in hydrocarbon
accumulation is analyzed according to the coupling
relationship between fault active periods and
hydrocarbon accumulation periods. Oil and gas
reservoir-controlling mode of faults is subdivided into
4 types: early accumulation-late preservation type,
early accumulation-late adjustment type, late
accumulation type and late dissipation type. The first
three types are main goals of oil and gas exploration
in western Qaidam basin, and deep reservoirs are still
the main target layers of exploration.
The unique strike slip-compressional tectonic settings
in northern Qaidam were formed due to intensively
strike slip and related compression in the late
Himalayan Period. The strike slip-compressional
tectonic system mainly composed of three types of
structures: broken strike slip -compressional structure
before mountain, broken strike-slip structure and
adjusted strike slip structure. Two stages of
hydrocarbon accumulation during the Himalayan
period and its combination with accumulation
conditions and structural formation determined the
continuing palaeo-structures since early Himalayan
period can be advantageous area for oil and gas
exploration in the northern Qaidam. But the
hydrocarbon distribution became complex due to the
adjustment and destruction of strike-slip tectonism.
The control of strike slip-compressional tectonic
system on hydrocarbon accumulation and distribution
and its combination with palaeo-structure, source rock
evolution and generation of oil and gas imply palaeostructure
flanks toward depression can be
advantageous exploration areas for hydrocarbon
enriched.
Key words: Qaidam basin, strike-slip compressional
tectonic system, hydrocarbon accumulation model,
differential accumulation, key controlling factor.
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