Changes

Economically significant concentrations of geothermal energy occur now where high temperatures (40° to more than 380°C; 104° to more than 716°F) are found in [[Porosity|porous]] and [[Permeability|permeable]] rocks at shallow depths (less than 3000 m; about 10,000 ft). The geothermal energy is stored in both the solid rock and the water or steam-filling pores and [[fracture]]s. The steam or hot water are used mainly as the fuel for the operation of electricity-generating turbines or for space heating.

Economically significant concentrations of geothermal energy occur now where high temperatures (40° to more than 380°C; 104° to more than 716°F) are found in [[Porosity|porous]] and [[Permeability|permeable]] rocks at shallow depths (less than 3000 m; about 10,000 ft). The geothermal energy is stored in both the solid rock and the water or steam-filling pores and [[fracture]]s. The steam or hot water are used mainly as the fuel for the operation of electricity-generating turbines or for space heating.

[[file:St54Figure48.JPG|thumb|200px|World geothermal electricity generation.<ref name=Salvador_2005>Salvador, A., 2005, Energy-A historical perspective and 21st century forecast: AAPG Studies in Geology 54, 208 p.</ref>]]

[[file:St54Figure48.JPG|thumb|200px|World geothermal electricity generation.<ref name=Salvador_2005>Salvador, A., 2005, Energy—A historical perspective and 21st century forecast: [http://store.aapg.org/detail.aspx?id=ADD-732 AAPG Studies in Geology 54], 208 p.</ref>]]

There are, therefore, three main requirements for the commercial development of geothermal resources: shallow high temperatures, rocks with good permeability, and sufficient volumes of water.

There are, therefore, three main requirements for the commercial development of geothermal resources: shallow high temperatures, rocks with good permeability, and sufficient volumes of water.

|competition=June 2015

|competition=June 2015

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=== Remaining heat and radioactive heat ===

=== Remaining heat and radioactive heat ===

* '''Geothermal Gradient''' is the variation of temperature according to a rock's depth. It is read in Celsius or Fahrenheit grades by the unit of vertical distance.  

* '''Geothermal Gradient''' is the variation of temperature according to a rock's depth. It is read in Celsius or Fahrenheit grades by the unit of vertical distance.  

* '''Surface Heat Flow''' is the heat that continuously comes up to the surface. It is read in joules per second. It is estimated that the average is 42 x 1012 J/sec and has two different sources:

* '''Surface Heat Flow''' is the heat that continuously comes up to the surface. It is read in joules per second. It is estimated that the average is 42 x 1012 J/sec and has two different sources (See [[:File:Figure 1.png|Figure 1]]):

** '''Remaining heat release''': 34 x 1012 J/sec. It comes from the [[mantle]] and the nucleus and is the heat remaining after the formation of the planet.

** '''Remaining heat release''': 34 x 1012 J/sec. It comes from the [[mantle]] and the nucleus and is the heat remaining after the formation of the planet.  

** '''Radioactive heat release''': 8x1012 J/sec. It comes from the [[crust]] and is produced by the fission of radioactive isotopes.

** '''Radioactive heat release''': 8 x 1012 J/sec. It comes from the [[crust]] and is produced by the fission of radioactive isotopes.  

See Figure 1

[[File:Figure 1.png|center|frame|{{figure number|1|}}Remaining heat and radioactive heat<ref>[https://www.mpoweruk.com/geothermal_energy.htm Electropaedia]</ref>.]]

=== Igneos phenomena ===

=== Igneous phenomena ===

In certain regions the geotermal gradient can be increased considerably due to magmatic process (Figure 2).Most of the áreas of goethermal interest are situated in volcanic regions.In many places of our planet,hydrotermal evidence can be seen on the surface provided that geologial conditions are favourable.[[File:Strokkur Geyser,Iceland.png|200|thumbnail|center|Figure 2: Igneos phenomena Strokkur Geyser,Iceland [http://www.stewartsmithphotography.co.uk/shop/uncategorized/strokkur-geysir-national-park-iceland/]. ]]

In certain regions the geothermal gradient can be increased considerably due to the magmatic process ([[:File:Strokkur Geyser,Iceland.png|Figure 2]]). Most of the areas of geothermal interest are situated in volcanic regions. In many places of our planet, hydrothermal evidence can be seen on the surface, provided that geological conditions are favorable.

[[File:Strokkur Geyser,Iceland.png|frame|center|{{figure number|2|}}Igneous phenomenon the Strokkur Geyser in Iceland<ref>[http://www.stewartsmithphotography.co.uk/shop/uncategorized/strokkur-geysir-national-park-iceland/ Stewart Smith Photography]</ref>. ]]

=== Plate Tectonics and heat distribution ===

=== Plate tectonics and heat distribution ===

The unequal distribution of the heat inside the Earth is what causes the movement of tectonic plates and all of  endogenous phenomena (Figure 3).All the áreas having higher heat flows are related to plate borders or Hot Spots.These higher flows are related,besides,to other parameters such as conrtical width,rocks thermic conductivity ,permeability, fluids ´ presence.etc.[[File: Distribution of surface heat flow.png|200|thumbnail|center|Figure 3:Distribution of surface heat flow [http://www.stewartsmithphotography.co.uk/shop/uncategorized/strokkur-geysir-national-park-iceland/].]]

The unequal distribution of the heat inside the Earth is what causes the movement of tectonic plates and all of  endogenous phenomena ([[:File:Distribution of surface heat flow.png|Figure 3]]). Areas having higher heat flows are related to plate borders or hot spots. These higher flows are related to other parameters such as width, thermic conductivity, permeability, fluid presence, etc.

[[File:Distribution of surface heat flow.png|frame|center|{{figure number|3|}}Distribution of surface heat flow.]]

==Kinds of Geothermal Deposits==

==Kinds of Geothermal Deposits==

=== Very low temperature deposits (T<30ºC) ===

=== Very low temperature deposits (T < 30°C) ===

: It is generally considered that temperature seasonal variations are percived only over the first 10 meters f the soil. After that there is a interval where the temperature is almost constant and it is considered that below 20 meters, the temperature increases three grades every 100 meters.Therefore ,all the planet is a source of geotermal resources of low temperature.These resources have domestic use.

It is generally considered that temperature seasonal variations are perceived only over the first 10 m of the soil. After that there is a interval where the temperature is almost constant and it is considered that below 20 m, the temperature increases three degrees every 100 m. Therefore, the whole planet is a source of geothermal resources of low temperature. These resources have domestic uses.

=== Low temperature fields (30ºC<T<90ºC) ===

=== Low temperature fields (30°C < T < 90°C) ===

: They are found in sedimentary basins with normal o hightly superior geotermal gradient.The sole condition is the existence of one or more aquifer horizons in adequate depths.Ej Paris Basin (France) ;Boise (EEUU) (Figure 4). [[File:Goethermal heating district, City of Boise, EEUU.png|thumbnail|center|Figure 4: Goethermal heating district. City of Boise. EEUU. [http://energy.ltgovernors.com/geothermal-resource-descriptions.html].]]

Low temperature fields are found in sedimentary basins with normal to high geothermal gradient. The sole condition is the existence of one or more aquifer horizons in adequate depths ([[:File:Goethermal heating district, City of Boise, EEUU.png|Figure 4]]).  

=== Medium temperature deposits (90ºC<T<150ºC) ===

[[File:Goethermal heating district, City of Boise, EEUU.png|frame|center|{{figure number|4|}}Geothermal heating district, Boise, Idaho.<ref>[http://energy.ltgovernors.com/geothermal-resource-descriptions.html Ltgovernors]</ref>]]

: They are foundin various places of our planet.They usually belong to áreas with specific geologic characteristics such as áreas of thin crust,higher concentration of radioactive isotopes or áreas close to or near [[igneous]] bodies.They can also be found over regions with higher gradient but a lower depth.They generally need an igneous intrusión and it is usual that,in this kind of field,water comes up to the surface forming hot springs.

=== Medium temperature deposits (90°C < T < 150°C) ===

Medium temperature deposits are found in various places of our planet. They usually belong to areas with specific geologic characteristics such as thin crust, higher concentration of radioactive isotopes, or near [[igneous]] bodies. They can also be found over regions with higher gradient but a lower depth.They generally need an igneous intrusion and often water comes to the surface, forming hot springs.

 

=== High temperature fields (T>150ºC) ===

=== High temperature fields (T>150ºC) ===

: These deposits are found in áreas of higher igneous activity.They are related to extremely high gradients, corresponding to global tectonic process.They occur in plate borders, cortical thinnes áreas or Hot Spots. They need an igneous source an aquifer and a impermeable layer to keep up pressure. In many cases there is surface evidence suchs as geysers and fumaroles, [[File: Simplified diagram of a geotermal power plant.png|thumbnail|center|Simplified diagram of a geotermal power plant. [http://www.bgs.ac.uk/research/energy/geothermal/].]]

High temperature fields are found in areas of higher igneous activity. They are related to extremely high gradients, corresponding to global tectonic process. They occur in plate borders, cortical thin areas or hot spots. They need an igneous source, an aquifer, and a impermeable layer to keep up pressure. In many cases, there is surface evidence such as geysers and fumaroles.

=== Hot dry Rock Deposits or Geotermal Stimulated Systems ===

 

: They are a kind of high temperature field but in wich the content off water and permeability is improved artificially by means of hydraulic fracture (the same method used in unconventional hydrocarbons resources).An example of this is the Soultz-sous-Forets Geothermal Field in France,where the heat source is a fractured granitic pluton

[[File: Simplified diagram of a geotermal power plant.png|frame|center|{{figure number|5}}Simplified diagram of a geothermal power plant.<ref>[http://www.bgs.ac.uk/research/energy/geothermal/ British Geological Survey]</ref>]]

 

===Hot dry rock deposits or geothermal stimulated systems ===

: They are a kind of high temperature field but in which the content of water and permeability is improved artificially by means of hydraulic fracturing (the same method used in unconventional hydrocarbons resources). An example of this is the Soultz-sous-Forets geothermal field in France,w here the heat source is a fractured granitic pluton.

==Extraction and uses==

==Extraction and uses==

[[File: Simplified diagram of a geotermal plant.png|frame|center|{{figure number|6|}}Simplified diagram of a geothermal plant.<ref>[https://www.linkedin.com/pulse/smart-grid-energy-harvesting-martin-ma-mba-med-gdm-scpm-pmp Linkedin article]</ref>]]

 

[[File: Simplified diagram of a geotermal plant.png|thumbnail|center|Figure 6. Simplified diagram of a geotermal plant [https://www.linkedin.com/pulse/smart-grid-energy-harvesting-martin-ma-mba-med-gdm-scpm-pmp].]]

==Sources==

==Sources==