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Paper Number: 193
Hydrocarbon migration
mechanism and accumulation model of ultra-deep carbonate rocks: a case
from China
Liu
Jingdong1, Jiang Youlu1 and Liu
Guagnxiang2
1School
of Geosciences, China University of Petroleum, Qingdao, 266580,
China
2Wuxi
Research Institute of Petroleum Geology, Research Institute of Petroleum
Exploration and Production, SINOPEC, Wuxi, 214162, China
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The great exploration potential of ultra-deep reservoirs has been
demonstrated again according to the discovery of Yuanba large gas field
in Sichuan basin of China. Its hydrocarbon migration mechanism and
accumulation model of ultra-deep carbonate rocks is established by the
analysis of the origin of natural gases, hydrocarbon migration pathways
and migrate directions in different stages. The origin of natural gases
is studied based on the source-reservoir contacting relationship, the
natural gas composition, carbon isotope and noble gas isotope. According
to the core observation, thin section and imaging logging analysis, the
types of hydrocarbon migration pathways are classified, the
configurations in different periods are also discussed. The directions
along which the natural gas may migrate are tracked according to natural
gas composition and carbon isotope.
The results show that the natural gas in the study area is oil
cracking origin, and the crude oil come from the underlying source rock
of Longtan Formation in Upper Permian. The pathways of hydrocarbon
migration are classified into fractured pathway, fractured-vuggy pathway
and intercrystal pore pathway. The oil migrates vertically along the
above three pathways under the control of relatively flat structure in
Middle Jurassic, and finally leads to the oil accumulation. In Late
Jurassic, the oil cracked into gas, and then under the influence of
uneven structural uplift formed in Cretaceous-Neogene, the migration of
natural gas began. The gas migrates towards the structural high part in
free phase or water-dissolving phase along the fractured pathway and
fractured-vuggy pathway. The hydrocarbon accumulation model in Yuanba
large gas field is as follows. In Middle Jurassic, oils were migrated
vertically and then accumulated. In Late Jurassic, oils were cracked
into natural gases in situ, and then natural gases were adjusted by
laterally migration in Cretaceous-Neogene.
