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Petroleum System of Carboniferous-Lower Permian in Western Tarim Basin, China
As early as 1986, when the first round of petroleum resources evaluation in the Tarim Basin was made, it was recognized that two sets of marine source rocks of Cambrian-Ordovician (C-O) and Carboniferous-Lower Permian (C-P1) were developed within the basin. However, since the campaign of Tarim exploration in 1989, some medium-large scale oil-gas fields were discovered in the craton area, with oil/gas coming mainly from C-O but the contribution of C-P1 source rocks not clearly established.
Based on oil/gas source correlation of two oil-gas fields, rock pyrolysis analysis
of about 500 samples from eight field sections and core and cuttings of eight wells, this paper presents a recognition of C-P1 petroleum system in the western Tarim Basin.
The oil/gas source correlation results of Ake gas
field, Kekeya condensate gas field in the Western Tarim Basin confirmed that
its oil-gas came from the C-P1 source rocks. High quality C-P1
source rocks were found in some outcrop sections from southern Tianshan
piedmont to Kunlun piedmont. By sampling densely in the developed segments of
C-P1 potential source rocks of eight wells in the northwest Tarim
Basin, analysis
data showed that Carboniferous source rocks have definite
hydrocarbon generation capacity with wider distribution, but Lower Permian
source rocks have relatively limited distribution. However, test results of
wells and sections indicated that the distribution of source rocks in different
formations/members showed lateral zonation and vertical intersecting
superposition, with possible multiple centers of hydrocarbon generation.
Through
analyzing gas reservoirs of Ake and Kekeya gas fields and outcrops of C-P1
oil seepage, the authors have found that C-P1 petroleum system
comprises of two sets of source-reservoir-cap assemblages. The former
constitutes a normal-type source-reservoir-cap assemblage. The latter is self
generating,
self
reservoiring and
self
sealing. Local structures were developed
in the Late Himalayan in the study area. At that time, C-P1 source
rocks were at the stage of over-mature or mature respectively, so all
structures were formed at or after the peak of gas generation, while faults
formed in this period acted as the pathway between source rocks and reservoir
beds. In a word, source rocks were well developed in Western Tarim Basin. And
the evolution of organic matter well matching with later formed structures
could make a prospective petroleum system in the Tarim Basin.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California