SOURCE ANALYSIS OF OIL SEEPAGE AND BITUMEN ORIGINATING FROM MARINE LAYER STRATA IN GUANGYUAN AREA, THE NORTHWEST SICHUAN BASIN

The reservoirs of Cambrian-Triassic from the Changjianggou section contain quantities of solid bitumen in Guangyuan area,the northwest Sichuan Basin.The oil seepage is abundant.It is suggested by research of absolute quantification analysis on the biomarkers of saturated hydrocarbon and aromatics that saturated hydrocarbon biomarker parameters of solid bitumen in Lower Cambrian and seepages in Devonian and Lower Permian Maokou Formation have similar characters.The results show that there is early hydrocarbon filling from Lower Cambrian source rock.There exist certain differences of aromatic biomarkers among them,which is perhaps influenced by late hydrocarbon filling from Upper Paleozoic besides of maturities.There are significant difference in biomarkers of saturated hydrocarbon and aromatics between seepages of Lower Triassic Feixianguan Formation and bitumen and seepages of Paleozoic.There is genetic relationship between seepage in Feixianguan Formation and source rock from Dalong Formation of Lower Permian,which also perhaps originates from Lower Triassic source rocks.