四川盆地原油裂解气的有利地温场分布及其演化特征

为了确定四川盆地原油裂解气的有利分布区,利用镜质体反射率古温标重建了四川盆地的热演化史,分析了四川盆地下三叠统飞仙关组原油裂解的有利地温场分布范围及其演化特征。结果表明:四川盆地各构造单元自三叠纪以来的热流演化是不一致的,川东北地区热流在地质历史时期最低,川中地区热流也较低,而川西北和川西地区热流演化最高,这种差异与青藏高原隆升及峨眉山玄武岩地幔柱有关;四川盆地在二叠纪时期热流明显高于其他时期,但高热流持续时间较短,这主要受岩浆侵入的影响;四川盆地飞仙关组原油裂解气的有利地温分布区是不断变化的,侏罗纪末期其几乎遍及整个四川盆地,白垩纪末期其范围缩小,古近纪末期其收缩至川西和川中部分地区,现今范围则最小,主要分布在川西部分地区;控制原油裂解气分布区的主要因素是古地温场,尤其是地温最高时期的地温场,而与现今地温场的关系并不密切。

Distribution and Evolution Characteristic of Favorable Geothermal Field for Oil Cracking Gas in Sichuan Basin

In order to sure the favorable area of oil cracking gas in Sichuan Basin,the thermal evolution history of Sichuan Basin was reconstructed by geothermometer of vitrinite reflectance,and the distribution and evolution characteristic of favorable geothermal field for oil cracking gas reservoirs in Feixianguan Formation of Lower Triassic were determined.The results showed that the heat flow evolution after Triassic was inconsistent in different tectonic units in Sichuan Basin;the heat flow was lowest in Northeast Sichuan,low in Central Sichuan,highest in Northwest Sichuan and West Sichuan during main geological ages,and the differences were mainly caused by the uplift of Qinghai-Tibet Plateau and basalt mantle plume of Emei Mountains;the heat flow was significantly higher during Permian than other periods,but the duration was short because of the magmatic intrusion;the distribution of favorable geothermal field for oil cracking gas in Triassic Feixianguan Formation was ever changing;the distribution was almost over Sichuan Basin at the end of Jurassic,and reduced at the end of Cretaceous,and continually reduced to West Sichuan and part of Central Sichuan,and was smallest and mainly in part of West Sichuan now;the distribution of oil cracking gas was mainly controlled by paleogeotherm,especially the geothermal field with highest geological temperature,but it had little relationship with contemporary geothermal field.