| Summary: | In order to clarify the source rock conditions and oil/gas potential of the Aixi Sag in the Yingen-Ejinaqi Basin, based on the analytical results of mudstone samples from two exploratory wells, a systematic evaluation of the source rocks was carried out in this paper, and the effective source rocks were supposed. The potential source rocks in the study area are mudstones developed in Cretaceous Wulansuhai Formation (K2w), Yingen Formation (K1y), Suhongtu Formation (K1s), and the third (K1b3), second (K1b2) and first member (K1b1) of Bayingebi Formation, among which the K1b3, K1b2 and K1b1 mudstones have the highest abundance of organic matter with the kerogen types of Ⅱ-Ⅲ at mature stages of thermal evolution. Elemental geochemical and biomarker data show that the paleoclimate during the deposition of source rocks was warm and humid, the sedimentary water was mainly fresh water, and the contribution of terrestrial organic matter was dominant. The favorite sedimentary paleoenvironment conducive to organic matter enrichment is high salinity and strong reducibility, and high productivity is the main controlling factor for the enrichment of organic matter. The lowest limit of TOC content of effective source rocks is supposed to be 0.85%, and the effective source rocks are mainly developed in K1b3, K1b2 and K1b1. They are mainly distributed in considerable areas in the southern, central, northern and western subsags. The total oil and gas resources in the study area are estimated to be around 5 091.05×104 t. Combined with the evidence of active oil and gas display, it is concluded that the study area has good oil and gas exploration potential.
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