| The ultra-deep carbonate rocks in the platform of the Tarim Basin become an important strategic replacement area for hydrocarbon accumulation.The drilling revealed that there are still liquid hydrocarbons in the ultra-deep carbonate rocks of the Cambrian and the Ordovician in the Tabei-Northern Aman area at the temperature above 150℃,breaking through the traditional occurrence temperature of crude oil reservoirs.However,the study of the ultra-deep geothermal field in the platform of the Tarim Basin is restricted due to the lack of effective paleotemperature scales.The present-day ultra-deep thermal regime and its influencing factors of the Tabei-Northern Aman area in the Tarim Basin were analyzed based on measured temperature data.According to the drilling data and calculated erosional thicknesses using the well-tie profiles,the sedimentary burial history of the Tabei-Northern Aman area was restored.On this basis,an effective method for reconstructing the thermal history of ultra-deep and ancient strata was established by combining carbonate clumped isotope,carbonate U-Pb,zircon(U-Th)/He,and equivalent vitrinite reflectance.The thermal history since the Paleozoic in the Tabei-Northern Aman area was revealed through a combination of multiple paleotemperature scales,and the thermal effect range of the large igneous province was delineated.Based on the results of thermal history,the temperature evolution of the Cambrian source rocks and the Ordovician reservoirs in the Tabei-Northern Aman was further restored,and the relationship between ultra-deep geothermal evolution and hydrocarbon accumulation was systematically analyzed in combination with the homogenization temperature of fluid inclusion assemblages and the geochemical properties of hydrocarbon.The mean values of the present-day geothermal gradients at depths of 0～5km and heat flow in the Tarim Basin are 21.6±2.9℃/km and 42.9±7.6m W/m~2,respectively,indicating that the Tarim Basin is a"cold"basin at the present-day.As a low-temperature area in the cold basin,the present-day formation temperature at the buried depths of6～10km has similar distribution characteristics of decreasing first and then increasing from north to south and decreasing from east to west on the plane,which is mainly related to the thermal lithospheric thickness,basement relief’s thermal structure,and rock’s thermophysical parameters.In particular,the present-day formation temperature in the Tabei-Northern Aman area is between 129.2℃and 197.2℃at the buried depths of 10km,and liquid hydrocarbons may still exist.The present-day formation temperature of the Cambrian and Ordovician bottom interfaces in the Tabei-Northern Aman area is107.0～171.0℃and 120.8～184.7℃,respectively.The present-day formation temperature of the Cambrian and Ordovician increase from northwest to southeast affected by the burial depth and heat flow,which match the geochemical properties of hydrocarbon.There experienced 10 periods of uplift and denudation in the Tabei-Northern Aman area,and the maximum erosional thickness was 800～4000m at the end of the Permian.Based on the sedimentary burial history and present-day ultra-deep thermal regime,this study revealed that the heat flow in the Tabei-Northern Aman area gradually decreased since the Cambrian and only the central and western regions experienced high abnormal peaks of 44～75m W/m~2 during the Early Permian,combined with carbonate clumped isotope,carbonate U-Pb,zircon(U-Th)/He,and equivalent vitrinite reflectance,and then the thermal effect range of the large igneous province was delineated.In addition,it has been pointed out that the different causes of the deep carbonate rocks experiencing peak temperatures of 170～210℃in different tectonic units include sedimentation and uplift in the Late Permian,mantle plume activity,and volcanic intrusion in the Early Permian.The Cambrian source rocks and the Ordovician reservoir in the Tabei-Northern Aman area experienced the evolution process of rapid warming-slow warming-rapid warming.In the key tectonic period,the high temperatures of these strata in the whole basin were concentrated in the depression area and the low temperatures were concentrated in the uplift area during the key tectonic period,which was jointly affected by the heat flow and the buried depth of the strata.Due to the influence of the geothermal field and sedimentary burial,there were four different thermal evolution patterns in the Tabei-Northern Aman,which also lead to different reservoir formation processes.This study not only provides support for the prediction of ultra-deep hydrocarbon phases,but also provides new insights for the study of ultra-deep thermal history,which is of guiding significance for understanding the formation and enrichment of ultra-deep oil and gas reservoirs in the Tarim Basin and similar basins around the world. |
