MAIN OIL SOURCE ROCKS AND OIL-SOURCE CORRELATION IN THE SIKESHU SAG, THE SOUTHERN MARGIN OF JUNGGAR BASIN

The risk exploration well Gaotan-1 was operated in 2019 on the Gaoquan east anticline of the Sikeshu Sag on the southern margin of the Junggar Basin. The Cretaceous Qingshuihe Formation was tested and obtained a daily high-yield oil-producing gas stream, confirming that the Sikeshu Sag is a potentially enriched area for oil and gas. In order to ascertain the oil and gas enrichment process in the Sikeshu Sag and clarify the future exploration direction, by collecting and sorting out the oil and gas geochemical data from key exploration wells, we made a detailed study in this paper on source rock evaluation, oil source comparison, and oil and gas migration characteristics. The results show that: ① Two sets of effective source rocks in the Badaowan Formation and Anjihaihe Formation respectively are well developed in the Kayindike area. The organic matters of the source rocks in the Badaowan Formation are dominated by types II₂ and III in low-maturity stage. The source rocks in the Anjihaihe Formation, however, must be buried deeper than 4 000 m to become effective source rocks; ② The West Lake anticline crude oil can be classified into types of A and B, corresponding to the argillaceous source rocks of the Jurassic Badaowan Formation in the Kayindike area and the coal series source rocks, and the original crude oil parent materials of Type A crude oil is better than that of Type B; ③ The crude oil in the Gaoquan structural area has no oil source relationship with the source rocks in Kayindike area. It is speculated that the crude oil from Well Gaotan 1 came from the piedmont hydrocarbon generation center in the south, and, therefore, the south is a favorable area for oil and gas exploration.