Crystalline basement focusing of heat versus fluid flow/compaction effects; a case study of the I-1 well in the Danish North Sea

The temperature distribution in the Danish Central Graben contains many local thermal anomalies, with the thermal gradient varying throughout the area from around 20 degrees Ckm (super -1) to about 55 degrees Ckm (super -1) . The presence of sub-surface salt structures of various shapes and sizes is responsible for many of the anomalies. In the case of the 1-1 well, however, four components can contribute to the observed thermal anomaly. (1) crystalline basement focusing of heat; (2) convection of heat from the deeper basin; (3) a local thermal anomaly due to salt or structure effects; and (4) the possible spatial variation of basement heat flux with position relative to the graben flank. While components (1), (2) and (3) do contribute to the thermal anomaly at the 1-1 well, they are not large enough to account for the anomaly without the presence of a local increase in basement heat flux of around 0.5 HFU (c. 21mWm (super -2) ).