The Paleogeothermal Field and Hydrocarbon Accumulation Period in Sartai Depression, Yabrai Basin

Key words: 
• Yabrai Basin /
• Sartai depression /
• Middle Jurassic /
• paleotemperature /
• hydrocarbon accumulation period

Abstract: In order to find out the relations between paleogeothermal field and hydrocarbon accumulation, vitrinite reflectance(Ro), apatite fission track(AFT) and homogenization temperature of fluid inclusions were discussed for revealing the paleotemperature. Hydrocarbon accumulation period was judged by the results of homogenization temperature of fluid inclusions based on the thermal history simulation. In the study area, the temperature of current-geothermal field is low and conductive with the geothermal gradient of 2.76 ℃/100m. The paleogeothermal field of each secondary tectonic unit in Sartai depression was different: The paleogeothermal field of Yanchang and Xiaohuzi sub-sag was conductive with the paleo-geothermal gradient of 2.8~3.4 ℃/100m and the paleotemperature was 81.2℃~128.1℃; The paleotemperature and paleo-geothermal gradient in Heisha Low Uplift were 103.2℃~140.2℃ and 4.2~4.8 ℃/100m, much higher than that in sedimentary depression because of the thermal polymerization and thermal anomaly of the low uplift. The Evolution of maturity was mainly controlled by paleogeothermal field,because the paleotemperature of Middle Jurassic was higher than the present. The analysis of thermal history simulation and hydrocarbon accumulation period show that the hydrocarbon filling process of the three second tectonic units are different. However, for the whole Middle Jurassic reservoir in Sartai depression, there were two times of hydrocarbon filling process happened at early stage of Late Jurassic (145.0~152.0 Ma)and Early Cretaceous(100.0~134.0 Ma)about the same time of peak paleogeothermal which reflected the importance of geothermal evolution in the process of hydrocarbon accumulation.