Heat flow and thermal modeling of the Yinggehai Basin, South China Sea

Geothermal gradients are estimated to vary from 31 to 43 degreesC/km in the Yinggehai Basin based on 99 temperature data sets compiled from oil well data. Thirty-seven thermal conductivity measurements on core samples were made and the effects of porosity and water saturation were corrected. Thermal conductivities of mudstone and sandstone range from 1.2 to 2.7 W/m K, with a mean of 2.0 +/- 0.5 W/m K after approximate correction. Heat flow at six sites in the Yinggehai Basin range from 69 to 86 mW/m(2), with a mean value of 79 +/- 7 mW/m(2). Thick sediments and high sedimentation rates resulted in a considerable radiogenic contribution, but also depressed the heat flow. Measurements indicate the radiogenic heat production in the sediment is 1.28 muW/m(3), which contributes 20% to the surface heat flow. After subtracting radiogenic heat contribution of the sediment, and sedimentation correction, the average basal heat flow from basement is about 86 mW/m2. Three stages of extension are recognized in the subsidence history, and a kinematic model is used to study the thermal evolution of the basin since the Cenozoic era. Model results show that the peak value of basal heat flow was getting higher and higher through the Cenozoic. The maximum basal heat flow increased from similar to65 mW/m(2) in the first stage to similar to75 mW/m(2) in the second stage, and then similar to90 mW/m(2) in the third stage. The present temperature field of the lithosphere of the Yinggehai Basin, which is still transient, is the result of the multistage extension, but was primarily associated with the Pliocene extension. (C) 2002 Elsevier Science B.V All rights reserved.