High-quality heat flow determination from the crystalline basement of the south-east margin of North China Craton

Abstract

Very few of heat flow data have come from the crystalline basement in the North China Craton but rather from boreholes in the sedimentary cover of oil–gas basins. Explorations for hot dry rock (HDR) geothermal resources and porphyry gold deposits in eastern China offer now valuable opportunities to study the terrestrial heat flow in the crystalline basement. In this study, we obtained continuous temperature logs from two boreholes (the LZ borehole with a depth of 3471m and the DR borehole with a depth of 2179m) located in the south-east margin of the North China Craton. The boreholes have experienced long shut-in times (442days and 261days for the LZ borehole and DR borehole, respectively); thus, it can be expected that the temperature conditions have re-equilibrated after drilling and drill-mud circulation. Rock thermal conductivity and radiogenic heat production were measured for 68 crystalline rock samples from these two boreholes. The measured heat-flow density was determined to be 71.8±2.3mWm−2 (for the LZ borehole) and 91.5±1.2mWm−2 (for the DR borehole). The heat flow for the LZ borehole is close to the value of 75mWm−2 determined in the Chinese Continental Scientific Drilling main hole (CCSD MH), both being in the Sulu-Dabie orogenic belt and thus able to verify each other. The value for the DR borehole is higher than the above two values, which supports former high heat-flow values determined in the Bohai Bay Basin.