Abstract:

A lot of physical and geochemical data of crude oils from Eastern Pearl River Mouth Basin show tnat all the oils are terrestrial-derived ones. The distribution of biomarkers,such as n-alkanes, isoprenoids, steranes, triterpanes and tricyciic terpanes in these oils was studied and lots of special biomarkers which were derived from terrestrial higher plants and fresh algae were discovered. This indicats that they were all sourced by both lacustrine Wenchang Formation mudstone and coaly Enping Formation deposited in Eocene and Eocene-Oiigocene terrestrial environment. Wenchang Formation was a good oil source with high hydrocarbon potential and Enping coaly source rock has been proved to be able to generate oil and gas. Both have therefore provided much abundant reserve of the oil and gas. Since many trap structures were formed earlier than main oil and gas expulsion periods, and the source-reservoir-cap rocks in the basin were well combined, the migration and accumulation of the oil and gas were very ideal. The geochemical migration parameters show that the oils found in Dongsha uplift underwent long distance migration. The migra-tory directions determined by the sterane parameter were coincident with those of important structural ridge, indicating that the oils migrated from oil generating depressions up to the traps in Dongsha uplift along the migratory pathways of the structural ridges, and thus the wide area of the uplift should be the important exploration target for searching big oil fields.