Effect of Lateral Fluid Flow on Thermal Structure of Crust

The earth’s temperature at shallow depths is influenced by diurnal and seasonal temperature variations at the ground surface. Below the influence depth of seasonal variations, the temperature generally increases with depth. The temperature–depth profile is usually linear in depth zones that are devoid of fluid flow. Perturbations to the linear temperature–depth relation occurs where thermal conductivity changes and/or anomalous heat sources are present. Topographic relief or climatic changes may also disturb the linear relation at shallow depths. In places where significant fluid flow exists, the isotherm can be so severely altered that the geothermal gradient is locally reversed. The development of geothermal systems and the factors that control their development are matters of considerable interest. The temperature–depth profiles are indicative of lateral hot water flow and conductive heat losses to the confined beds. These temperature data can be analyzed to yield the recharge rate into the hydrothermal system and its time and evolution. Interpretation of the measured temperature–depth profile is often based on the assumption of conductive heat transfer outside the main part of the geothermal system and on temperature that increases linearly with depth. Some temperature–depth profiles do not exhibit an increasing temperature with increasing depth. A characteristic temperaturedepth profile has a linear increase of temperature at shallow depths and a decrease in temperature at greater depths. The geothermal gradient may again become positive so that an increase in depth produces an increase in temperature. The phenomena of these temperature inversions can be due to fluid flow within a thin horizontal or shallowly dipping fracture or aquifer ( Bodvarson, 1973 ). A characteristic temperature-depth profile in the presence of hot fluid flow (continuous line curve) and an undisturbed temperature–depth profile in the absence of hot fluid flow (dotted line curve) are shown in Fig. 1 . Figure 1 A schematic diagram of the flow model with temperature–depth profiles in the presence of fluid flow (continuous line) and in the absence of fluid flow (dotted line). A line graph showing temperature-depth profiles with fluid flow and without fluid flow. https://www.w3.org/1999/xlink" xlink:href="#long-desc40"/> https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003762133/83422fd9-f5c1-4e82-86cf-a450bf71b60e/content/fig11_1.tif "/>