Present-day geothermal field and thermal history of the Zhanhuadong Block,Jiyang depression

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 refl ectance(R-O)data. The results indicate that (1) The average present geother mal gradient is 35.8 degrees /km, showing a decreasing trend with depth;hig her geothermal gradient more than 37 degreesC/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 m W/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 oi l bearing layers experienced long term slowly heating process under a reaso nable burial depth,they are still in the 'oil-generating window' with a wid e depth range. The geothermal evolution in the Zhanhuadong Block is good fo r oil generation. The reconstructed thermal history results support the vie wpoint that Bohai Bay is a rift basin and is of practical significance to t he oil exploration in the studied area.