Hydrocarbon generation potential and oil-bearing property of the Chang 73 sub-member shale in the Jiyuan area of the Ordos Basin: a case study of Well J119H2

Although the hydrocarbon potential of the Chang 7 Member has been well documented, the oil-bearing characteristics and expulsion efficiency of the Chang 73 sub-member remain poorly constrained, highlighting the need for this investigation. Systematic analysis of the hydrocarbon generation potential, trace elements, and paleontology of the dark shale in the Chang 73 sub-member of Well J119H2 in the Jiyuan area has clarified the hydrocarbon generation potential and oil-bearing characteristics of shale in this interval. The results indicate that the total organic carbon values of the dark mud shale rang from 0.32 to 13.76% and S1 + S2 values are between 0.10 and 43.09 mg/g. The main types of kerogen are Type I and Type II1, consistent with high-quality lacustrine shales in the Songliao Basin that have demonstrated commercial shale oil production. The trace element indicators reflect that the black shale was mainly deposited in a warm and stratified anoxic-reducing environment, and the paleo-productivity was high during the shale sedimentation period. The residual total oil content of shale oil is calculated to be between 5.64 and 14.16 mg/g. Compared with other major continental shale oil production zones in China, the total organic carbon values and residual total oil content of the Chang 73 Member in Well J119H2 suggest favorable hydrocarbon generation potential, placing it on par with China’s most productive continental shale oil systems, including those in the Songliao and Junggar Basins. The contribution ratio of dark mudstone to shale to oil and gas resources in the study area is 1:1.8. Overall, the Chang 73 shale oil in the Jiyuan area demonstrates significant exploration potential.