PRESENT-DAY GEOTHERMAL FIELD AND THERMAL HISTORY OF THE ZHANHUADONG BLOCK, JIYANG DEPRESSION
CHENG BEN HE (Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China) XU LIANG\ XIANG XI YONG MU XING (Institute of Geology,Shengli Oilfield, dongying 257015,China)
Present day geothermal field in the Zhanhuadong Block,Jiyang depression,is analyzed based on available borehole temperature data.The thermal history is reconstructed using tectonothermal modeling costrained by vitrinite reflectance( R O)data. The results indicate that (1) The average present geothermal gradient is 35.8℃/km, showing a decreasing trend with depth;higher geothermal gradient more than 37℃/km in Gudao and Kendong area is observed. (2) The heat flow evolution is associated with multi episodic rifting processes. The Palaeo heat flow reached the maximum of about 83.6 mW/m 2 in the early Paleocene corresponding to the major rifting stage,and then cooled down with pulsant variation corresponding to minor rifting to the present day regional average heat flow 63mW/m 2. (3) Since the main oil bearing layers experienced long term slowly heating process under a reasonable burial depth,they are still in the ‘oil generating window’with a wide depth range. The geothermal evolution in the Zhanhuadong Block is good for oil generation. The reconstructed thermal history results support the viewpoint that Bohai Bay is a rift basin and is of practical significance to the oil exploration in the studied area.