Geochemical characteristics of source rocks and resource potential in Sayin Hudug Trough, Eerdeng Sum Sag, Erlian Basin

Although significant hydrocarbon exploration achievements have been made in the Sayin Hudug Trough of the Eerdeng Sum Sag, Erlian Basin, systematic studies on source rocks remains limited, and the resource potential is still unclear. Based on test and analytical data, a systematic evaluation of the source rocks in the study area was conducted. The study predicted the distribution of effective source rocks and clarified the oil and gas resource potential of this area. Research results showed that source rocks in the A'ershan Formation (K₁ba) of the Sayin Hudug Trough in the Eerdeng Sum Sag had relatively high organic matter abundance, was more humic, and was in a mature stage of thermal evolution, making them the main source rocks of the trough. In addition, the first member of the Tengger Formation (K₁bt₁) also showed relatively good source rock development in certain areas, such as in the northern sub-trough, and could serve as a secondary source rock. Geochemical characteristics varied across different sub-troughs, mainly in organic matter abundance. For example, the average total organic carbon (TOC) of K₁ba source rocks in the northern sub-trough was 1.15%, slightly higher than the 0.97% in the southern sub-trough. Biomarker compound and trace element data showed that both K₁ba and K₁bt₁ source rocks were formed in freshwater sedimentary environments of semi-humid to semi-arid climates under weak reduction and weak oxidation conditions. The organic matter was mainly derived from mixed inputs of aquatic organisms and higher plants, with higher plants having a slight biogenic advantage. The lower limit of TOC content for effective source rocks was determined to be 1.0%. Effective source rocks were mainly distributed in the sedimentary centers of the three secondary structural units, i.e., northern, middle, and southern sub-troughs. The total oil resources in the Sayin Hudug Trough were predicted to be 54.188 7×10⁶ t. The southern sub-trough had the greatest oil and gas potential, followed by the northern sub-trough.