Study on Sedimentary Environment and Model of Paleogene Source Rocks in the Southern Margin of the Junggar Basin

Abstract：The hydrocarbon source rock of the Paleogene Anjihaihe Formation (E2+3a) in the the Junggar Basin, China, is a set of potential hydrocarbon source rock strata. Previous studies on the Paleogene mainly focused on structural characteristics [1-2], sedimentary sequences [3-4], reservoir development characteristics [5], etc., and the study area mainly focused on a small number of outcrops and drilling points. There are few studies on the development environment and model of E2+3a source rocks in the the Junggar Basin like foreland background, which directly affects the evaluation of E2+3a oil and gas exploration prospects. Therefore, the author uses outcrop, drilling, seismic, geochemical analysis and other data to analyze the sedimentary environment of hydrocarbon source rocks based on the filling characteristics of Paleogene source rock structure and sedimentary formation under the quasi foreland background, and jointly uses lithology combination, paleontology combination, geochemical element analysis. The research results show that from the Paleogene to now, the southern edge of the the Junggar Basin has formed a geological background of rapid subsidence, high formation pressure, and low geothermal gradient. The source rocks of the Anjihaihe Formation in the Paleogene are mainly distributed in the southern and central regions of the basin, with a maximum thickness of 250-300m. The organic matter abundance is relatively high, and the organic matter type is I-II1 type, with a Ro value of 05% -0.8%, belonging to medium to good source rocks. The stepwise analysis of multiple factors identified high paleoproductivity, anaerobic reduction environment, and slow sedimentation rate as the main controlling factors for the development of high-quality E2+3a source rocks. The saline water environment provides nutrients for plankton and forms high productivity. Deeper water bodies form a reducing environment, which is conducive to the preservation of organic matter. The input of lower terrestrial debris material forms a low sedimentation rate, slowing down the dilution of organic matter. Keywords: The Junggar Basin, China; Paleogene; Source rocks; Sedimentary environment and sedimentary pattern References [1]Fang, S. H., Guo, Z. J., Zhang, Z. C., Wu, C. D., et al. (2004) Discussion on Mesozoic-Cenozoic Evolution of Tian Shan and Its Adjacent Basins. Universitatis Pekinensis (Acta Scientiarum Naturalium), 40(6):886-897. [2]Zhu, M., Wang, X., Xiao. L. X. (2020) Structural Characteristics and Evolution in the Southern Margin of Junggar Basin. Xinjiang Petroleum Geology, 41(1):9-17. [3]Zhou, C. M., Cheng, J. H., Shi, T. M., He, C. Q. (2012) Geological Age and Paleoenvironmental Significance of the Upper Part of the Middle Anjihaihe Formation in the Southern Margin of the the Junggar Basin, Xinjiang. Journal of Stratigraphy, 36(4):723-732. [4]Wang, Y. Z., Wu, C. D., Ma, J., et al. (2019) Strata color rhythm of the Cretaceous-Neogene and evolution of palaeoenvironment and palaeoclimate in Junggar Basin. Journal of Palaeogeography(Chinese Edition), 21(3):451-468. [5]Zhang, L. Q., Li, X. G., et al. (2011) Calcite cements in Paleogene sandstone of Anjihaihe formation,Junggar Basin. Petroleum Geology and Recovery Efficiency, 18(5):6-8.