XU MIN, Curtin University of Technology, School of Applied Geology, Perth, Australia
ABSTRACT: Syn- and Post-Rift
Petroleum
Systems in the Songliao Basin, China
The non-marine, extension-related, Songliao basin is one of the most
important oil and gas-producing basins in China. It consists of Cretaceous syn- and
post-rift successions, with contrasting features of petroleum
systems. The syn-rift
successions in the Songliao area developed in 32 fault basins, all of which were overlain
by a post-rift succession. The source rocks of syn-rift
petroleum
(gas)
system
developed
in some coal-bearing sections in the fluvial and lacustrine sequences. Geochemical data
indicates that these source rocks contain humic kerogen, which produced the main gas pools
in the Songliao basin. The Late Cretaceous post-rift source rocks developed in the
Qingshankou and Nenjiang Formations, representing the primary flooding surface and maximum
flooding surface, respectively. They are dominated by lacustrine mudstones containing
sapropelic kerogen which provide oil-favourable source beds as well as some oil-associated
gas. The widely distributed post-rift
petroleum
system
is the main hydrocarbon-producing
systems in the Songliao basin. Geochemical studies on trace elements, dinosterane and C31
sterane of the post-rift successions suggest the existence of a temporary marine
transgression in the Late Cretaceous, which resulted in deepening of basins and formation
of mudstone rich in organic matter. This can explain the existence of the favorable
petroleum
system
in the post-rift succession in the Songliao basin, rather than in the
syn-rift succession, although the average heatflow, subsidence rate and thermal gradient
are higher in syn-rift stage than that in post-rift stage.
AAPG Search and Discovery Article #90909©2000 AAPG Foundation Grants-in-Aid