Terrestrial Heat Flow in Non-Thermal Ground Water Circulation Settings of Brazil

Hamza

2019

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The present work provides a new look into the nature and distribution of geothermal resources of South America, on the basis of recent advances in data analysis and regional assessments. Notable in this context is the progress achieved in the use of a procedure termed as magmatic heat budget (MHB) that allow estimation of heat flux in areas of recent volcanic activity. In addition, an updated compilation of temperature gradients and heat flux have been completed. Such advances have allowed new resource assessments for 6526 sites. These span over more than 100 crustal blocks, distributed in thirteen countries of the continent. Following this, a 2ox2ogrid system with homogenized data sets were employed for calculating the in-situ heat content. Determinations of resource base based on observational data are now available for 253 out of a total of 418 cells in this grid system. Values of resource base based on estimated heat flow were calculated for the remaining 165 grid elements. The data and model results on temperatures of subsurface strata at depths less than three kilometers have been employed in classifying the resources, into three general categories: hot dry rock (HDR), hot wet rock (HWR) and low enthalpy (LE). HDR type resources, classified as those with temperatures higher than 150oC, occur in 318 localities mainly in the Andean regions. Similarly, HWR type resources, classified as those with temperatures in the range of 90 to 150oC, occur in 352 localities. Low enthalpy (LE) resources, with temperatures < 90oC, are numerous mainly in the eastern parts of the continent. The total resource base (RB) of HDR systems is estimated to be 1329x1021J and the corresponding resource base per unit area (RBUA) is 513GJ/m2. The HWR systems have a total resource base of 586x1021J, while the corresponding value for RBUA is 409GJ/m2. The low enthalpy systems, with temperatures in the range of 60 to 90oC, have a total resource base of 240GJ/m2, while those with temperatures less than 60oCis estimated to be 210GJ/m2. There are indications that HDR resources, with temperatures higher than 150oC at depths less than three kilometers, occur in 318 localities of the Andean regions. The total resource base (RB) of HDR systems is estimated to be 1329x1021J, while the corresponding weighted mean resource base per unit area (RBUA) is estimated to be 513GJ/m2. The new results have also been useful in regional scale identification of resources with notable pore fluid circulation, classified as HWR systems. Such systems with temperatures in the range of 90 to 150oC, are inferred to occur at depths less than three kilometers, in 352 localities of the Andean region. The total resource base of HWR systems is estimated to be 586x1021J, while the corresponding value for RBUA is estimated to be 409GJ/m2. Low enthalpy (LE) resources, with temperatures in the range of < 90oC, are numerous in the remaining parts of Andean regions and also in the eastern parts of the continent. The resource base per unit area of low enthalpy systems with temperatures in the range of 60 to 90oC is estimated to be 240GJ/m2, while that for systems with temperatures less than 60oCis estimated to be 210GJ/m2.

Section: Modifications In the Gcl Methodsmentioning

confidence: 99%

Assessment of Geothermal Resources of South America - A New Look

Hamza

2019

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“…In addition, geochemical data acquired by Geological Survey of Brazil (CPRM/SBG, 2006) in ninety-four groundwater wells were employed for determining reservoir temperatures based on silica geothermometry techniques (Fournier and Truesdell, 1973;Fournier, 1989;Swanberg e Morgan, 1978 and. Recently, the methodology used in reservoir temperature estimates from concentrations of dissolved silica (SiO2) was reassessed by Alexandrino and Hamza (2018). Examples of temperature log data and procedures employed in determination of temperature gradients are illustrated in Figure 3 for wells in Santa Maria and Cristalandia.…”

Section: Methodsmentioning

confidence: 99%

“…Figure 4 illustrates examples of the use of BHT data acquired in oil wells (left panel) and the geochemical method (GCL) based on the silica content in groundwater wells (right panel). Details of the GCL method has been discussed in detail by Swanberg and Morgan (1978) and more recently by Alexandrino and Hamza, 2018).…”

Section: Methodsmentioning

confidence: 99%

Regions of anomalous geothermal fields in the State of Tocantins, Central Brazil

Descovi

2019

We report recent progress in determination of geothermal gradients and heat flow in the State of Tocantins, Central Brazil. This region lying between the Amazonas and Sao Francisco cratons has been affected by metamorphic folding events (Brasilia and Araguaia) during Proterozoic times. This area is also characterized by moderate micro-seismic seismic activity. Results of recent investigations have revealed the presence of several areas where geothermal gradients and heat flow have values higher than normal, which is considered atypical of stable tectonic settings. In southern parts of the State of Tocantins heat flow values are higher than 80 mW/m2. Extrapolations based on near surface heat flow data point to crustal temperatures in excess of 200°C at depths less than 5 km. However, there are no evidences of magmatic intrusions at shallow intra-crustal depths. In the absence of other geologic source mechanisms and tectonic events the process responsible for high heat flow has been postulated to be enhanced heat transport by carbonic gas flow in the upper crust. This possible alternative is supported by observations of carbonic gas flow at sites of thermal springs within the study area and also in geothermal areas in the neighboring state of Goiás. Model simulations of deep crustal geotherms indicate that temperatures may approach levels of partial fusion at the crust mantle boundary.

“…where TSiO2 is the reservoir temperature derived from the silica content of thermal waters, m is a constant related to the depth of circulation of thermal waters and b is the mean annual surface temperature, referred to in Equation 6. Alexandrino and Hamza (2018) The relation for heat flux derived from Equation 7 may also be written as:…”

Section: Model Considerationsmentioning

confidence: 99%

“…The values of heat flow q0 and reservoir temperature TSiO2, in Table 1, were estimated by Alexandrino and Hamza (2018), using the geochemical method (silica concentration) for the main Brazilian tectonic provinces, as shown in Figure 4. The value of surface temperature (T0) used was estimated by Alexandrino and Hamza (2018) based on Figure 3 and its value is 25.5±6.7 ºC. The values assumed for specific heat of the fluid (cW) has been 4.18 kJ/ºC and the density of the fluid (W) 1000 kg/m 3 .…”

Section: Tests Using Observational Datamentioning

confidence: 99%

Method for estimating the depth of circulation of thermal and non-thermal waters in the upper crust

Alexandrino

Hamza

2021

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In this work we consider model formulations that allow better understandings of the relations between Darcy velocity and temperatures in coupled two-dimensional systems. The revised theoretical formulations are capable of accounting for the effects of heat transfer by fluid movements in horizontal and vertical directions. The models have been found useful in estimating the maximum and minimum depths of thermal and non-thermal waters in several geological units in Brazil. The best fitting values encountered are 1.8 to 2.7 km for the Paraná basin, 2.0 to 2.8 km for the Parnaiba basin, 1.6 to 2.3 km for the Amazon basins, 2.0 to 2.7 km for the San Francisco Province, 1.9 to 2.4 km for the Sergipe-Alagoas basins and 2.0 to 2.8 km for the Borborema Province. The models have also allowed estimation the average values of Péclet number and Darcy velocity for groundwater flows in these units. Note that higher horizontal velocities are associated with smaller depths of circulation. This is a natural consequence of the fact that in systems where horizontal velocities are high the quantities of vertical flows are less intense.