Abstract: The hydrocarbon-generating organisms in the source rocks of the Paleogene Shahejie Formation in the Dongpu sag were studied by optical microscopy and SEM. Results show that such organisms are well developed and various in types, including dinoflagellate, green algae, cyanobacteria and coccolithophores. Major combination of hydrocarbon-generating organisms developed in saline water area of the northern Dongpu Sag include dinoflagellate, cyanobacteria and coccolithophores, all of which can form algal laminae. In contrast, major combination of hydrocarbon-generating orgnisms developed in freshwater area of the southern Dongpu Sag include green algae and higher plants, which are developed in massive mudstone. Thermal simulation experiments were conducted on
two samples taken from saltwater and freshwater areas, respectively. It is showed that cyanobacteria and coccolithophores in saline water area have high hydrocarbon generation potential and low oil generation threshold, and can generate large amount of oil at low maturity stage, and the controlling factor of producing low maturity oil is cyanobacteria. The oil generation threshold of dinoflagellates and green algae is higher, among which dinoflagellates are important hydrocarbon generation organisms because of their large amount of biomass. Algae in the freshwater area have lower hydrocarbon generation potential and higher oil generation threshold than dinoflagellates.

Key words: dinoflagellates, cyanobacteria, coccolithophores, thermal simulation