Lowest limit of organic carbon content in effective source rocks from Lucaogou Formation in Jimusar Sag

The generation and organic geochemical features of source rocks from the Lucaogou Formation in Ji174 well area in the Jimusar Sag of the Junggar Basin were studied. According to hydrocarbon expulsion laws as well as the relationships between soluble organic matter transformation rate, pyrolysis S₁/w(TOC) and organic carbon content, the lowest limit of organic carbon content for hydrocarbon expulsion in lutaceous source rocks was determined. In the Lucaogou Formation in Ji174 well area, lutaceous source rocks developed well, and their hydrocarbon generation conditions were similar even though the lithology was various. Due to the differences in mineral compositions and organic matter characteristics, the lowest limit of organic carbon content for hydrocarbon expulsion was different. For pure lutaceous, silty, calcareous and dolomite source rocks, the lowest limits were 2.50%,2.80%,1.45% and 1.30%, respectively. The carbonate-containing effective source rocks took larger proportions than pure and silty mudstones, all over 50%. It was concluded that in the Lucaogou Formation in Ji174 well area, lutaceous effective source rocks were well-developed, and the lowest limits of organic carbon content were higher, which were favorable for hydrocarbon reservoirs.