Organic matter inputs and depositional palaeoenvironment recorded by biomarkers of marine‐terrestrial transitional shale in the Southern North China Basin

Abstract

In recent years, significant breakthroughs have been achieved in shale gas exploration and exploitation of marine and continental shales in petroliferous basins of China. As an important petroliferous basin in China, marine–terrestrial transitional shale was widely distributed among the Southern North China Basin (SNCB). However, biomarkers distribution characteristics of marine–terrestrial transitional shale in the SNCB, which can reveal the organic matter inputs and paleoenvironmental characteristics, is not widely concerned. In general, organic matter in a transitional environment can be affected by the amounts of organic matters input from fresh water and aquatic organisms from the sea. To systematically investigate the organic geochemical characteristics of biomarkers in marine–terrestrial transitional shale from SNCB, core samples from the Upper Shihezi, Shanxi and Taiyuan formations were obtained from a single borehole in the SNCB. Gas chromatography–mass spectrometry (GC–MS) analysis was conducted on the saturated hydrocarbons. n‐Alkanes, acyclic isoprenoid alkanes, terpanes, and steranes were detected to study the change in organic matter inputs and sedimentary paleoenvironment of the marine–terrestrial transitional shale. The results reveal that organic matter inputs obviously changed during the sedimentary period in the study area of the SNCB. In addition, the terrestrial higher plants contributed more organic matter to shale from the Upper Shihezi Formation compared to the Taiyuan Formation and the Shanxi Formation. The shift of organic matter inputs is consistent with marine regression in the Early Permian period, which may significantly influence the organic matter input characteristics. Meanwhile, the marine–terrestrial transitional shale, including samples from the Taiyuan, Shanxi and Upper Shihezi formations, was deposited in a relatively oxic condition during the depositional process.

Study on Sedimentary Environment and Organic Matter Enrichment Model of Carboniferous–Permian Marine–Continental Transitional Shale in Northern Margin of North China Basin

“…Among them, multiple sets of marine-continental transitional shale distributed in the Carboniferous-Permian system in the northern North China Basin are characterized by diverse kerogen types, large changes in organic matter abundance, high maturity, and medium clay abundance. They have become the current research hotspots for the exploration and development of shale gas [14][15][16].…”

Multi-Isothermal Stage Pyrolysis of the Chang 73 Shale Oil Reservoirs, Ordos Basin: Implications for Oil Occurrence States and In Situ Conversion Exploitation

“…The successful exploitation of unconventional resources represented by shale oil and gas in North America enables the United States to achieve energy independence and drives the upsurge of global shale oil and gas exploration with significant reference. , China’s technically recoverable shale oil resources reached 145 × 10 8 t in 2016 and are mainly distributed in several large sedimentary basins, including the Songliao Basin, Junggar Basin, Ordos Basin, and Bohai Basin. − Among them, shale oil in the Ordos Basin is mainly concentrated in the Chang 7 (Ch-7) subsection, which is a sedimentary combination of laminar-foliated mudstone and shale (Mu&Sh) rich in organic matter (OM) as well as delta front-gravity flow siltstone and sandstone (Si&Sa) in the peak period of the lacustrine basin . What should be explicit is that the major exploration breakthroughs at present are chiefly in the Ch-7 1 and Ch-7 2 subsections dominated by gravity flow and delta front sand body deposition, and the lithology is mainly multistage superimposed thick Si&Sa with thin Mu&Sh .…”

Response model of fluid–rock ratio to reservoir space in primary formation of shale oil during hydrous pyrolysis

“…However, different from marine shale in North America, continental lacustrine shale in China has complex mineral compositions, abundant rock types, rapid phase transformation and strong reservoir heterogeneity. Organic-rich shales can be formed in different sedimentary environments and undergo compaction, diagenesis, tectonism and the superimposition of geological fluids, resulting in the diversity and complexity of shale pore and fracture systems (Loucks & Ruppel 2007;Abouelresh & Slatt 2012;Bai et al 2018Bai et al , 2020Liu et al 2022).…”