松辽盆地北部白垩系青山口组温压演化及其与古龙页岩油富集关系OA

The temperature-pressure history of the organic-rich shale in the Cretaceous Qingshankou Formation in the northern Songliao Basin was reconstructed through comprehensive analyses,including field tests,paleo-heat flow reconstruction,overpressure evolution and geochemistry.The formation and evolution process of the Gulong shale oil was reproduced,and its enrichment patterns were clarified.Influenced by tectothermal events and tectonic movements at the end of the Cretaceous Mingshui Formation deposition,the evolution of organic matter thermal maturity in the first member of Qingshankou Formation(Qing-1 Member)exhibited distinct stages,which can be divided into the Cretaceous rapid evolution stage and the Paleogene-Neogene slow evolution and stabilization stage.High paleogeotemperature drove secondary cracking of retained oil in the Qing-1 Member,forming light shale oil in the Gulong Sag.This sag experienced three phases of overpressure during the late depositional stage of the Nenjiang Formation and late depositional stage of the Mingshui Formation of the Cretaceous,and the Neogene.The first two phases were related to the oil generation peak and secondary cracking in the sag,respectively,while the third phase resulted from the inheritance of earlier overpressure,as well as sustained hydrocarbon cracking and heat-induced fluid volume expansion.Crude oil is distributed orderly in the northern Songliao Basin.Conventional oil reservoirs such as Saertu and Putaohua contain high contents of non-hydrocarbon compounds,and they are believed to have formed by hydrocarbon charging as a result of the first phase of overpressure.Tight oils in the Fuyu and Gaotaizi reservoirs,most similar to shale oil in the Qing-1 Member in terms of composition and physical properties,are characterized by high content of saturated hydrocarbons,with their hydrocarbon charging and accumulation related to the second phase of overpressure.High paleo-heat flow generated by tectothermal events is determined to be the main driving factor for the staged hydrocarbon generation of organic matter in the Qingshankou Formation.The shale of Qing-1 Member with high thermal conductivity and the Cretaceous Nenjiang shale with low thermal conductivity constitute a thermal structure with lower conducting and upper sealing.This structure has prolonged secondary cracking of hydrocarbons,widened the liquid hydrocarbon window,and helped self-sealing enrichment of the Gulong light shale oil by virtue of the third phase of overpressure.