Geothermal measurements in the pilot-boreholes of the china continental scientific drilling

The geothermal measurements in the pilot boreholes of the China Continental Scientific Drilling (CCSD) indicate that the temperature gradients in the target area of the deep drilling range from 19 to 26°C/km, which is lower than that (25–0°C/km) for the global continental area and similar to that for the KTB (21–28°C/km). Ther mal conductivity measurements for 44 core samples show that the ultra-high pressure (UHP) metamorphic rocks have 50% higher thermal conductivity (with a mean of 3.94±1.26 W/mK) than that for the average value of the upper crust. The measured heat flow values vary between 76 and 80 mW/m², higher than that for the global continental area (65±1.6 mW/m²) and the continental China (61±15.5 mW/m²) as well as the adjacent North Jiangsu Basin (68 mW/m²), but lower than that below 1000 m in the KTB (85 mW/m²). The elevated heat flow in the pilot-boreholes can be attributed to the lateral heat concentration due to higher rock thermal conductivity of the UHP belt than that of the adjacent rocks. Lower deep temperature in the target area of the deep drill ing can be expected due to the lower measured temperature gradient, which means that the Sulu area is geothermally suitable for continental deep drilling.