Study On Cenozoic Tectono-thermal Evolution Of Marginal Subsags In The Jiyang Depression

In long-term-runing petroliferous provinces in the eastern China,principal part of main sags are successively entering into a high exploration and development phase,thus the marginal subsags distributed around the sags become potential replacement areas for hydrocarbon production.Tectono-thermal evolution is a key content in the study of basin dynamics and hydrocarbon accumulation,which,on one hand,reflects the thermodynamical processes of formation and development of sedimentary basins,on the other hand,controls the thermal maturity evolution of depositional organic matters in the sedimentary basins.Therefore,the study on tectono-thermal evolution of these marginal subsags plays an important role in understanding their thermodynamical evolution and hydrocarbon potential.By analyzing three thermochronometers,apatite fission track,apatite(U-Th)/He and vitrinite reflectance,this thesis reconstructed thermal history of 30 typical wells from 13 marginal subsags in the Jiyang Depression,as a whole indicating a decreasing average geothermal gradient since the Paleogene:46?/km?50?/km at the end of the Paleogene,38?/km?46?/km in the Late Oligocene,34?/km?38?/km in the Middle-Late Miocene and?35?/km at the present;and a similar decreasing average heat flow:85 mW/m~2?89 mW/m~2 at the end of the Paleogene,75 mW/m~2?81 mW/m~2 in the Late Oligocene,67 mW/m~2?73 mW/m~2in the Middle-Late Miocene and 65 mW/m~2?70 mW/m~2 at the present.Based on the recovered thermal history,erosion amount of the Dongying Formation in typical wells during the Dongying Movement were estimated thtough geothermal method,which ranges from 256.1 m to 536.6 m.Maturity evolution of main source rocks in typical wells were also modeled,indicating that there is a considerable difference of present source rock maturity amoung margional subsags and temperature determined by burial depth is the mian factor controlling the maturity of source rocks.The Member 3 and 4of Shahejie Formation began to enter into early maturity stage at the depth of?2000 m;however,some wells were perturbed by magmatic thermal anomalies,and researched high maturity stage not long after burial,forming the phenomenon of“shallow burial but high maturity”.In addition,the zircon fission track ages from the Qingxi and Niuzhuang subsags could be decomposed into 4 groups of age peaks:60 Ma?68 Ma?110 Ma?130 Ma?200 Ma?240 Ma and 500 Ma?550 Ma,suggesting that the Cenozoic sources materials of these tow subsags were probably multiply-provided by the Binxian,Chenjiazhuang,Kendong,Weibei and Guangrao uplifts around them.The close temperature of(U-Th)/He system in detrital apatite obtained from natural drillhole in marginal subsags of the Jiyang depression is ?80?,higher than the result of ?75?derived form thermal simulation experiments.