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Earth of fire

Actualité volcanique, Article de fond sur étude de volcan, tectonique, récits et photos de voyage

Although at the tip of the geothermal exploitation, Iceland is still search the hottest water, even in a state called supercritical (*) , to be used in its geothermal plants. The supercritical water is preferred because it carries a higher amount of energy .

Water is supercritical when its temperature and pressure are above the critical point , characterized by 
Tc = 374°C and Pc = 221 bar. The water in this state present amazing physicochemical properties, intermediate between liquid and gas.

image2This exploration is done by the Iceland Deep Drilling Project ( IDDP ) , a government consortium.
 Krafla - Viti maar - AVE copie
Krafla - the Viti maar in the foreground , and the vapors of the geothermal power plant - photo Antony Van Eeten

First drilling in this context was created in 2009 in Krafla, where geothermal power plant gets since 1977 already hot water drawn from terrestrial bowels, by 18 wells. Its transformation into steam during its ascent to the surface feeds two turbines of 30 MW.

IDDP project
        IDDP project - left, deep drilling planned - right, the depth reached by conventional drilling.

Krafla magma chamber - (Adapted from Stefánsson, 1981.)
The Krafla magma chamber - position of geothermal installations - doc . Krafla magma chamber - ( Adapted from Stefánsson , 1981. )

The 2009 project was to dig a deep well to reach a pocket of supercritical water at a depth of 4,500 meters. However arrived at 2096 meters , the mechanical stresses between the drill bit has suddenly dropped ... a pocket of magma had been pierced .
This accident has offered the opportunity to study magma that flowed into the geothermal exploration wells. This is a rhyolitic magma having a temperature between 900 and 1000 ° C.

worldsfirstm - Krafla 2009 -Kristján Einarsson.
                 Krafla 2009 - doc . worldsfirstm - photo Kristján Einarsson .

After this "relative" failure in 2009, a steel device was placed at the bottom of the well, where it was cemented near the magma. This device was perforated molten rock side to recover the hot water ( 440 ° C , at a pressure of 22MPa ) . The steam flowing to the surface fueled turbines of the Krafla power plant until July 2012. Accelerated corrosion of certain equipment by HCl present in the vapor then forced to stop this operation and wells are closed.

Tests conducted at Krafla have however demonstrated that we can drill in a magma pocket, while controlling the situation, and then produce renewable energy by taking advantage of the molten lava.

Krafla experience opens new perspectives for the exploitation of geothermal resources.

ft6v19p151 00204 (306x347)
The drilling in Krafla, in the north, and the Reykjanes Peninsula , southwest , are located in areas of active rifting and high temperature (gray lined)

A new drilling to reach the supercritical water is provided for 2014-2015 , on another place : the Reykjanes peninsula, southwest Iceland, situated as Krafla on the active rift zone .

( * )  The critical point of a pure substance is the point of a curve connecting pressure, temperature and density such that the phase transition between the liquid and gaseous state is impossible - the density of the two states of the body considered now being of the same value from that point , as the refractive index in the gaseous state and the liquid state, regardless of the previous state ( liquid or gaseous ) .

Supercritical, in physical chemistry , is the state of the material when subjected to high pressure or temperature. We speak of supercritical fluid when fluid is heated above its critical temperature and when it is compressed above its critical pressure . This state of matter was discovered in 1822 by Charles Cagniard de Latour . The physical properties of a supercritical fluid ( density , viscosity , diffusivity ) are intermediate between those of liquids and gases.

 

 

Sources :

- IDDP - Iceland Deep Drilling Project - Drilling into supercritical geothermal systems - link

- Origin of a rhyolite that intruded a geothermal well while drilling at the Krafla volcano, Iceland By W.A. Elders   & al. - 2010.

- Iceland Deep Drilling Project: The first well, IDDP-1, drilled into magma - by W.A. Elders

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