Temperature-depth Measurements Research Articles

Deduction of the Dimensionless Groups and Type Curves of Temperature Profiles in Two-Layer Soils with Water Flow at Depth

In the common hydrogeologic scenarios of horizontal groundwater flow and a water table below the surface, the steady-state 2D thermal field resulting from the coupling between water flow and heat flow and transport gives rise to a vertical temperature profile that develops progressively over a finite extent of the domain. Beyond this region, the temperature profiles are linear and independent of horizontal position. Such profiles are related to the groundwater velocity so they can be usefully used to estimate this velocity in the form of an inverse problem. By non-dimensionalization of the governing equations and boundary conditions, this manuscript formally derives the precise dimensionless groups governing the main unknowns of the problem, namely, (i) extent of the profile development region, (ii) time required for the steady-state temperature profile solution to be reached and (iii) the temperature–depth profiles themselves at each horizontal position of the development region. After verifying the mathematical dependencies of these unknowns on the deduced dimensionless groups, and by means of a large number of accurate numerical simulations, the type curves related to the horizontal extension of the development of the steady-state profiles, the characteristic time to develop such profiles and the dimensionless vertical temperature profiles inside the characteristic region are derived. These universal graphs can be used for the estimation of groundwater horizontal velocities from temperature–depth measurements.

Temperature-depth curves and heat flow in central part of Anatolia, Turkey

The objective of this study is to determine the crustal thermal regime of Central Anatolia Province and its relationship with regional tectonics. Investigations include new temperature-depth measurements in wells, calculations of geothermal gradients from new and previously measured temperature logs, and determinations of heat flow with terrain corrections if necessary. The results provide us with a better understanding of the regional distribution of subsurface temperatures and heat flow within the study area. Although Central Anatolia Province is bordered with tectonically active areas, moderate heat flow values (64 ± 16 mW m−2) are generally observed within the region in accordance with the relatively less tectonic activity. Two thermally anomalous zones are indicated in the vicinity of Kırşehir and Kızılcahamam with heat flow values of higher than 100 mW m−2. Anomalous heat flow in these areas can best be explained by high radioactivity of basement rocks although this is not directly confirmed for the Kızılcahamam anomaly. The high elevation and recent volcanic activity in the region indicate that thermal activity may be present at lithospheric levels but have not yet reached up to crustal levels. Also, no surface heat flow anomaly due to fault activity was observed at the section of the North Anatolia fault within the study area.

Geothermal energy characterization in the Appalachian Basin of New York and Pennsylvania

Analysis of geothermal energy resources in the Appalachian Basin of the eastern United States is of interest, given the region’s population- and climate-driven demand for thermal energy. This study provides a fuller picture of geothermal resources across New York and Pennsylvania than previous studies by providing a rigorous statistical analysis of temperature-depth data using records from nearly 8000 locations. The compilation of thousands of temperature-depth data enables a significant increase in the spatial resolution of geothermal resource assessment maps for this region. In addition, this project has contributed to the compilation of geothermal data at a national level through the National Geothermal Data System. These temperature-depth measurements are byproducts of historical and recent drilling for petroleum and natural gas in the sedimentary basin. Bottom hole temperatures (BHTs) were recorded before the wells reached thermal equilibrium and at a wide range of depths. To extract a comprehensive description of the thermal state of the Appalachian Basin strata required application of both a BHT correction scheme and a simple thermal model. The model results for individual wells were combined with geostatistical interpolation employing kriging to produce maps that reveal significant variations in subsurface thermal gradient and surface heat flow with markedly improved spatial resolution. An area in south-central New York State displays favorable geothermal resource potential, with heat flow estimates of 50–60 mW/m 2 . There are 2 elongate, 200–300 km long, northeast-trending bands of favorable geothermal resource potential in central and western Pennsylvania, with heat flow of 55–90 mW/m 2 .

Shape Optimization Methods Locating Layer Interfaces in Geothermal Reservoirs

Subsurface structures have a strong influence on fluid flow and heat transport in geothermal systems. We examine whether the position and shape of an interface between two lithological bodies can be detected based on temperature-depth measurements. We use a level set function to describe the interface, and a shape optimization method in combination with the adjoint variable based on the heat transport equation to invert for position and shape. Specifically, we investigate how advective heat transport affects the identification of the interface and show that the method successfully retrieves interface positions in synthetic 2D cases of two-layer models.

XBT profilers for operational purposes: application and validation in real exercises

A methodology for recovering salinity from expendable bathythermograph (XBT) data is presented. The procedure exploits climatological relationships between temperature, salinity and depth to build regional characteristic curves by fitting a polynomial function that minimises both the variance of residuals and unknowns. Hence, salinity is computed and recovered as a function of temperature and depth. Empirical formula are provided to recover the salinity field from temperature-depth measurements for the Cantabrian Sea and Galician Area. The method is validated and applied in the context of two marine rescue exercises carried out in the Bay of Biscay close to the north coast of Spain and in the Finisterre region, where a series of XBT and conductivity-temperature-depth (CTD) profiles were acquired during fast samplings. The results agree reasonably well with independent data in terms of the spatial structure, with the largest errors in the upper 100 m of the ocean and at intermediate levels. The first diagnoses of the surface geostrophic velocity fields obtained through the salinity reconstruction are coherent and may help in rescue and safety operations during marine emergencies. Hence, we recommend that a technical unit should consider this kind of expandable sampling strategy with both XBT and XCTD data during marine emergencies, since it provides useful and comprehensive information rapidly with minimal interference by means of formal operations on board search and rescue ships.

Age of Crary Ice Rise, Antarctica, Determined from Temperature-Depth Profiles

Temperature-depth measurements from two sites on Crary Ice Rise, Antarctica are analyzed to deduce the time the ice first grounded at each location. At the thicker site (480 m), the best estimate of the time since grounding is 1100 years. At the shallower site (369 m) the grounding is more recent, 580 years ago, and there is evidence that basal cooling was delayed for 450 years while water at the base was freezing. This analysis leads to the conclusion that Crary Ice Rise was formed by at least two separate grounding events and is not a remnant of a more extensive grounded ice sheet which occupied the present position of the Ross Ice Shelf.

Age of Crary Ice Rise, Antarctica, Determined from Temperature-Depth Profiles

Temperature-depth measurements from two sites on Crary Ice Rise, Antarctica are analyzed to deduce the time the ice first grounded at each location. At the thicker site (480 m), the best estimate of the time since grounding is 1100 years. At the shallower site (369 m) the grounding is more recent, 580 years ago, and there is evidence that basal cooling was delayed for 450 years while water at the base was freezing. This analysis leads to the conclusion that Crary Ice Rise was formed by at least two separate grounding events and is not a remnant of a more extensive grounded ice sheet which occupied the present position of the Ross Ice Shelf.