Basin modelling and source rock characteristics of the Late Palaeoproterozoic Cuizhuang Formation in the Yuncheng sub‐basin, North China: Implications for hydrocarbon generation and expulsion history

The present investigation is the first to provide information on the formation, process and influence factors for hydrocarbon generation and expulsion potential of the Cuizhuang Formation source rock in the Yuncheng sub-basin to decipher the reason why no commercial petroleum resources have been found so far. In this study, data from the Jitan-1 well in the Yuncheng sub-basin were applied for the Cuizhuang Formation source rock basin modelling and organic geochemical analyses to reconstruct the burial and thermal evolution history and reveal the timing and process of hydrocarbon generation and expulsion. The modelling results indicate that the peak palaeotemperature of the Cuizhuang Formation source rock reached similar to 205"C in the Middle Carboniferous (similar to 327 Ma) at a maximum burial depth of similar to 4000 m, when rapid burial subsidence and thermal events played a significant role in increasing thermal maturity. The Cuizhuang Formation generated and expelled small amounts of hydrocarbons from the Early Ordovician until the Middle Carboniferous, starting with the primary kerogen cracking and conversion to oil from the Early to Middle Ordovician (similar to 476-461 Ma), corresponding to the thermal maturity values of 0.55-0.70 %VRo and transformation ratio (TR) <10%. The expulsion of most generated oil (0.70-1.30 %VRo, TR of 10%-90%) started from the Middle Ordovician to the Early Carboniferous (similar to 461-351 Ma), before reaching the secondary cracking of the retained oil into gas (>1.30 %VRo and TR of 90%-100%) from the Early to Middle Carboniferous (similar to 351-327 Ma). Destruction of the initial formation of hydrocarbon reservoirs in the Yuncheng sub-basin was primarily controlled by the Middle Carboniferous tectonic event with its major uplift-erosion, resulting in the absence of potential hydrocarbon reservoirs in recent exploration activities in some parts of the Yuncheng sub-basin.