Sequence stratigraphy of the Eocene deep-water organic-rich mudstones in the Fushun Basin, Northeast China

Sequence stratigraphy study in mudstone and oil shale strata is difficulty but critical for the analysis of the quality unconventional oil and gas reservoirs. This contribution investigates the sequence stratigraphy of the Eocene thick organic-rich fine-grained sediments in the Fushun basin, according to the organic geochemical data measured in laboratory and predicted by the amplitude difference the resistivity and the density curve when they are overlapping (which was called Delta logR). The sampling interval of Delta logR was 0.125 m. The results show that the total organic carbon, the oil yield, and the petroleum potential of the Eocene mudstones prove a good linear correlation between values measured in lab and values predicted by the Delta logR model. A total of 21 parasequences are identified in mudstones and can be divided into two cycles, a fully developed lower cycle and an underdeveloped upper cycle. There are four organic matter accumulation stages in a fully developed cycle, including two stages in the uprising half-cycle characterized by low values and rising values of the predicted geochemical data, respectively, followed by two stages in the declining half cycle characterized by high values and decreasing values of the predicted geochemical data, respectively. This contribution provides a basis for a further analysis of the characteristics of organic matter cycles in the oil shale strata of the Fushun Basin and areas with similar situation.

Automated summary

The study of sequence stratigraphy in mudstone and oil shale strata is crucial for analyzing the quality of unconventional oil and gas reservoirs. This research focuses on the Eocene thick organic-rich fine-grained sediments in the Fushun basin and investigates the sequence stratigraphy using organic geochemical data and the Delta logR model. The results demonstrate a good linear correlation between the values measured in the lab and those predicted by the Delta logR model. Further analysis reveals 21 parasequences in mudstones, which can be classified into two cycles.