Thermal Evolution And Petroleum-charging Times In The Northeast Area Of Ordos Basin

The thermal evolution and petroleum-charging times of the Upper Paleozoic hydrocarbon reservoir in the Northeast area of Ordos Basin is a hot issue of tectonic dynamic research and hydrocarbon exploration. There are several petroleum-charging times in the study area. Based on the recognition of unconformity-tectonic evolution and present geothermal field characteristics, through thermal history modeling of apatite fission trace, the Meso-Cenozoic tectonic thermal history in the Northeast area of Ordos Basin is revealed. Combined with methods of fluid inclusions and illite K-Ar date, analysis gas accumulation times of the Upper Paleozoic gas reservoir and relationship of between the tectonic-thermal history and the gas accumulation times.(1) Based on the formation construction and unconformity relationship of interface, clear the not integrate event and tectonic sequence framework in the Northeast area of Ordos Basin, as well as the three stages of tectonic evolution in Meso-Cenozoic.(2) The present geothermal field results show that the geothermal gradient is concentrated in the 2.7-3.0℃/100m, heat flow changes in the 58-70mW/m2, the characteristics is south higher than north of the northeast basin, as well as geothermal field is mainly controlled by the deep heat flow changes.(3) By AFT Solve thermal history modeling and simulation-based data, exploring and establishing tectonic thermal evolution model in the Northeast area of Ordos Basin. There is 120±lOMa tectonic thermal event in Mid-Yanshan and Combined with paleogeothermal gradient evolution, show that study area has undergone four tectonoic thermal evolution stages:Slow buried warming tectonic evolution stages in low paleogeothermal gradient background in Triassic to late Jurassic. Rapid warming tectonic evolution stage in high paleogeothermal gradient background in late Jurassic to Early Cretaceous. Paleotemperature gradually reduced tectonic evolution stages in higher paleogeothermal gradient background in Early Cretaceous to Paleogene. The formation rapid uplift and cooling tectonic evolution stages in low paleogeothermal gradient background since late Paleogene.(4) Fluid inclusion thermometry and illite dating comprehensive of hydrocarbon sandstone results show: there are least three petroleum-charging times in the Northeast area of Ordos Basin: Early petroleum-charging time mainly occur in late Jurassic(175-155Ma); Mid-Yanshan petroleum-charging time concentrated Early Cretaceous(135-125Ma); Early hydrocarbon adjustment and oil-gas escape in Paleogene 30Ma.(5) By analysis comparison relationship of between tectonic thermal history and gas accumulation time of the Upper Paleozoic hydrocarbon reservoir, the formation warming process in the early and middle of Yanshan is closely related with two original accumulation of the Upper Paleozoic hydrocarbon reservoir, the tectonic thermal event in Mid-Yanshan is the main factor for large-scale original accumulation of the Upper Paleozoic hydrocarbon reservoir. The late significant tectonic uplift and cooling events occurred mainly in the 60～30Ma, and caused hydrocarbon adjustment and late second generation of the Upper Paleozoic gas reservoir.