| According to the principles of systematic, dynamic and comprehensive, the characteristics of source rocks and their thermal evolution history in Hefei basin are mainly studied. Firstly, with the comprehensive analyses of tectonic-lithofacies palaeogeography and source rocks features, the organic abundance of the source rocks in different sequences and their lithofacies distributions are discussed. Secondly, by means of the comprehensive methods of multi-testing with vitrinite reflectance(Ro) and apatite fission track(AFT), the paleo-thermal fields of the basin and the evolution history of the source rocks are researched. Also, the favorable areas and targets are predicted for future petroleum exploration of the Hefei basin.At present, Hefei basin could be divided into three tectonic elements from south to north: depression zone in south , taphrogen zone in central part and clinoform zone in north. It is a multi-cyclic sedimentary basin during the Mesozoic and the Cenozoic, and has undergone four stages of tectonic evolution: (1)the Jurassic compressive depressional stage, (2)the Early Cretaceous shear-compressive-depressional stage, (3) the Late Cretaceous to Eogene extensional faulted stage, and (4)the Neogene to Quaternary reconstructive stage.The features of source rocks in Hefei basin are revealed by organic abundance analyses of the source rocks in different sequences. The Lower Cambrian marine mudstone, the Carboniferous-Permian coal-bearing mudstone, and the Eogene lacustrine mudstone are relatively good source rocks, otherwise, the lacustrine mudstones of Cretaceous and Lower Jurassic are relatively bad source rocks. The Eogene source rocks, as well as the Cretaceous, mainly are oil source rocks with low to middle mature degrees. The deeper source rocks of the Lower Jurassic and its substrata mainly belong to gas source rocks with postmature degrees. Furthermore, the lithofacies distributions of the different source rocks are revealed by analyses of tectonic-lithofacies palaeogeography of the source rocks. The Upper Paleozoic source rocks distribute in the lying side of basement fault zone in form of wedge zone or in the middle-northern part of Dingyuan depression. The Jurassic source rocks distribute in the middle part of basin. The Lower Cretaceous source rocks distribute in the middle-southern part of Daqiao depression. The Upper Cretaceous source rocks mainly distribute in Dingyuan and Shucheng depression.By studying the thermal history of the Hefei basin with analyses of Ro and AFT, it is showed that the basin has experienced at least three stages of tectonic-thermal evolution during Mesozoic and Cenozoic. Such as: ?the high paleo-geothermal stage during the Early Cretaceous with the gradients about 67~113°C/km in different areas and near 67°C/km in relatively stable areas, ?the middle paleo-geothermal stage during the Late Cretaceous to Eogene with the gradients about 36-40 °C/km, (3) the low paleo-geothermal stage during the Neogene to Quaternary with the gradient about 27.5 °C /km. Moreover, by the combination of the history of tectonic, sedimentary and burial of the Hefei basin, it is discovered that the primary generative period of the source rocks of the Upper Paleozoic, the Jurassic, and the Lower Cretaceous is mainly occurred at the Early Cretaceous. The primary generative period of the source rocks of the Upper Cretaceous and the Eogene is about the middle to the end of the Eogene. The hydrocarbon generation of all source rocks in the basin has been restrained or stopped since Neogene.Also, according to the principle of the petroleum system-from source to trap, the favorable areas and targets are predicted for the future petroleum exploration of the Hefei basin. There are three most favorable targets, such as Muchangbu, Sangjianzi, andYandian; five more favorable targets, such as Xiaomiao, Feixi, Shijiaji, Wushanmiao, and Fanghushan; four less favorable targets, such as Zhuxiang, Shushang, South- Daqiaonan, and South-Muchangbu.
|
PDF Full Text Request