鄂尔多斯盆地三叠系镜质体反射率与地热史

VITRINITE REFLECTANCE IN TRIASSIC WITH RELATION TO GEOTHERMAL HISTORY OF ORDOS BASIN

鄂尔多斯盆地庆３６井三叠系镜质体反射率为０．６１％～１．０６％，其碳化梯度（Ｒｍ／ｋｍ）较高，达０．３６％。运用不同方法分析表明，该盆地中生代古地温梯度可达３５～５７℃／ｋｍ，高于现今地温梯度。其它地温分析结果支持这一推论。推测高古地温梯度的原因可能是中生代时地壳厚度较薄和中侏罗世末一期热事件。讨论了高古地温梯度对于油气形成与勘探的影响。

Vitrinite reflectance of dispersed organic matter in Triassic of well Qing 36 in Ordos basin(i.e.Shanganning basin) range from 0.61% to 1.06%,yielding a higher coalification gradient of 0.36% R_m/km.According to different analyses ,it is concluded that the palaeogeothermal gradients in the Mesozoic could be up to 35-57℃/km and exceed present geothermal gradients(22-27℃/km).Other geothermal analyses (microthermometry of fluid inclusions and occurrence of laumonite)support this conclusion It is inferred that the higher palaeogeothermal gradients may be attributed to either a thinner crust during Mesozoic,or to a short thermal event at the end of Middle Jurassic,or to both of them.The higher palaeogeothermal gradients played an important role in the formation of hydrocarbons,and have significant influence on oil and gas exploration.