Abstract: The accurate knowledge of geothermal regime of sedimentary basins holds importance for investigating basin formation dynamics and hydrocarbon potential assessment as well. The Qiongdongnan Basin is a key area of deep-water hydrocarbon exploration and development in the northern South China Sea, but the geothermal regime of the deep water area in the basin is still open. Combined the corrections of formation temperature data of 21 new drilling wells with measured rock thermal properties, the basic characteristics of the present-day geothermal field in the Qiongdongnan Basin were presented here. Our results show that the heat flow data in the study area are mainly concentrated in the range of 60-90 mW/m2, with the mean of 73.2±8.67 mW/m². Most of the geothermal gradients in the study area are concentrated in 30-50℃ / km, with an average of 39.4±4.86℃ / km. In addition, both the heat flow and the geothermal gradient show the similar trend and featured by higher in deep-water area and lower in the shallow water area. The average heat flow of the deep-water area is 16 mW/m2 higher than that in the shallow water area. The average geothermal gradient for the deep-water area is 10℃ /km higher than that in shallow water. This is mainly due to the differential extension and thinning of the lithosphere and thermal blanketing effects of the sediments. In addition, there is an anomaly high heat flow zone in the Changchang sag, with the mean of 94.5±6.4 mW/m2, which is the results of Late-Miocene magmatic intrusion and fracture activities. The results mentioned could provide new geothermal parameters for basin modeling and hydrocarbon potential assessment of the Qiongdongnan Basin.

Key words: heat flow, geothermal gradient, geothermal regime, Qiongdongnan Basin