The southern Ordos Basin has excellent petroleum exploration prospects.However,the tectono-thermal history and the controls on petroleum generation,accumulation and preservation conditions in southern basin are unclea...The southern Ordos Basin has excellent petroleum exploration prospects.However,the tectono-thermal history and the controls on petroleum generation,accumulation and preservation conditions in southern basin are unclear.In this study,we analyzed the present geothermal field,paleo-geothermal gradient,maturity of the hydrocarbon source rocks,uplift and cooling process and tectono-thermal evolution history.In the study area,for the Ordovician,Permain and the Triassic strata,the present temperature is low(3070℃)in the southeastern area but high(80140℃)in the northwestern area.The paleogeothermal gradient varied from 24℃/km to 30℃/km with a heat flow of 58—69 m W/m^(2)(i.e.,a medium-temperature basin).The paleo-temperatures are higher than the present temperatures and the maximum paleo-temperatures controlled the thermal maturity of the source rocks.The vitrinite reflectance(Ro)values of the Triassic strata are>0.7%and the thermal maturity reached the middlemature oil generation stage.The Rovalues of the Permian-Ordovician strata are>1.8%and the thermal maturity reached the over-mature gas generation stage.The southern Ordos Basin has experienced the multiple tectonic events at the Late Ordovician Caledonian(452 Ma),Late Triassic(215 Ma),Late Jurassic(165160 Ma),End-Early Cretaceous(110100 Ma)and Cenozoic(since 40 Ma).A large-scale tectonothermal event occurred at the End-Early Cretaceous(110100 Ma),which was controlled by lithospheric extension,destruction and thinning.This event led to the highest paleo-temperatures and thermal maturities and coeval with the peak period of petroleum generation and accumulation.The southern Ordos Basin has undergone rapid and large-scale uplift since the Late Cretaceous due to expansion of the northeastern margin of the Tibetan Plateau,uplift of the Qinling orogenic belt and thrust faulting in the Liupanshan tectonic belt.The southern Ordos Basin experienced tectonic overprinting that was strong in the south and weak in the north.The strongest overprinting occurred in the southwestern part of the basin.The large-scale uplift,denudation and faulting led to oil and gas loss from reservoirs.The petroleum generation,accumulation and preservation in the southern Ordos Basin were affected by deep lithospheric structures and the tectono-thermal evolution.This work provides a novel tectono-thermal perspective on the petroleum generation,accumulation and preservation condition of the southern Ordos Basin.展开更多
The thermal evolution of source rocks in the Paleozoic has long been a problem to petroleum exploration in the Bachu uplift, Tarim basin, since the thermal history in the Paleozoic could not be rebuilt objectively due...The thermal evolution of source rocks in the Paleozoic has long been a problem to petroleum exploration in the Bachu uplift, Tarim basin, since the thermal history in the Paleozoic could not be rebuilt objectively due to lack of effective thermal indicators in the Lower Paleozoic successions. The apatite and zircon （U-Th）/He thermochronometry can be used as a new kind of technique to study the thermal history and tectonic uplift of sedimentary basins. Based on the measured apatite and zircon （U-Th）/He ages, apatite fission track data and equivalence vitrinite reflectance （%EVRo）, the tectonothermal histories in 5 wells of the Bachu uplift were modeled. The modeling results show that there was relatively high gradient at the Early Paleozoic in the Bachu uplift and it decreased gradually during the entire Paleozoic： 33-35℃/km in the Cambrian- Ordovician, 32-33℃/km in the Silurian-Devonian, 30-32℃/km at the end of Carboniferous and 27.5- 31℃/km at the end of Permian. Therefore, the thermal history can be modeled by combining multiple thermal indicators of AFT, （U-Th）/He ages and EVRo data. Especially, this provides a new method to rebuild the thermal history for the Low Paleozoic carbonate successions in the Tarim Basin.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.42102164,42241204,41630312and 42272174)the Petro China Changqing Oilfield Company Science and Technology Major Project(ZDZX 2021-01)。
文摘The southern Ordos Basin has excellent petroleum exploration prospects.However,the tectono-thermal history and the controls on petroleum generation,accumulation and preservation conditions in southern basin are unclear.In this study,we analyzed the present geothermal field,paleo-geothermal gradient,maturity of the hydrocarbon source rocks,uplift and cooling process and tectono-thermal evolution history.In the study area,for the Ordovician,Permain and the Triassic strata,the present temperature is low(3070℃)in the southeastern area but high(80140℃)in the northwestern area.The paleogeothermal gradient varied from 24℃/km to 30℃/km with a heat flow of 58—69 m W/m^(2)(i.e.,a medium-temperature basin).The paleo-temperatures are higher than the present temperatures and the maximum paleo-temperatures controlled the thermal maturity of the source rocks.The vitrinite reflectance(Ro)values of the Triassic strata are>0.7%and the thermal maturity reached the middlemature oil generation stage.The Rovalues of the Permian-Ordovician strata are>1.8%and the thermal maturity reached the over-mature gas generation stage.The southern Ordos Basin has experienced the multiple tectonic events at the Late Ordovician Caledonian(452 Ma),Late Triassic(215 Ma),Late Jurassic(165160 Ma),End-Early Cretaceous(110100 Ma)and Cenozoic(since 40 Ma).A large-scale tectonothermal event occurred at the End-Early Cretaceous(110100 Ma),which was controlled by lithospheric extension,destruction and thinning.This event led to the highest paleo-temperatures and thermal maturities and coeval with the peak period of petroleum generation and accumulation.The southern Ordos Basin has undergone rapid and large-scale uplift since the Late Cretaceous due to expansion of the northeastern margin of the Tibetan Plateau,uplift of the Qinling orogenic belt and thrust faulting in the Liupanshan tectonic belt.The southern Ordos Basin experienced tectonic overprinting that was strong in the south and weak in the north.The strongest overprinting occurred in the southwestern part of the basin.The large-scale uplift,denudation and faulting led to oil and gas loss from reservoirs.The petroleum generation,accumulation and preservation in the southern Ordos Basin were affected by deep lithospheric structures and the tectono-thermal evolution.This work provides a novel tectono-thermal perspective on the petroleum generation,accumulation and preservation condition of the southern Ordos Basin.
基金The National Major Fundamental Research and Development Project(2005CB422102)Notional Key Project for Oil and Gas(2008ZX05007-03)Key Project of SINOPEC provided financial support for this work
文摘The thermal evolution of source rocks in the Paleozoic has long been a problem to petroleum exploration in the Bachu uplift, Tarim basin, since the thermal history in the Paleozoic could not be rebuilt objectively due to lack of effective thermal indicators in the Lower Paleozoic successions. The apatite and zircon （U-Th）/He thermochronometry can be used as a new kind of technique to study the thermal history and tectonic uplift of sedimentary basins. Based on the measured apatite and zircon （U-Th）/He ages, apatite fission track data and equivalence vitrinite reflectance （%EVRo）, the tectonothermal histories in 5 wells of the Bachu uplift were modeled. The modeling results show that there was relatively high gradient at the Early Paleozoic in the Bachu uplift and it decreased gradually during the entire Paleozoic： 33-35℃/km in the Cambrian- Ordovician, 32-33℃/km in the Silurian-Devonian, 30-32℃/km at the end of Carboniferous and 27.5- 31℃/km at the end of Permian. Therefore, the thermal history can be modeled by combining multiple thermal indicators of AFT, （U-Th）/He ages and EVRo data. Especially, this provides a new method to rebuild the thermal history for the Low Paleozoic carbonate successions in the Tarim Basin.
