Geothermal Solution

3 Geothermal Solution 9.4.3.1 From Where Does It Come  

Below the crust of our planet is a reservoir of geothermal energy coming from the original formation of the planet about 4.5 billion years ago (20%) and from radioactive decay of minerals such as uranium, thorium, and potassium (80%). 

Geothermal derives from the Greek geo means earth and thermal means hot. The difference in temperature between the core of the planet and its surface implies that there is a geothermal gradient that moves the thermal energy in the form of heat from the core to the surface of the earth. This is the major factor involved in accessibility of geothermal energy the second factor is the permeability of the rocks near the surface of the earth, which determines the rate of heat conduction to the surface. 

Geothermal sources may either be low temperature ( 149 °C) or high temperature. Low-temperature sources are most appropriate for direct application, such as the production of hot water for homes or for heat. A closed loop recycle system includes a well drilled up to 400 ft into the ground to extract high underground temperatures 

CURRENT AND FUTURE STATE OF ENERGY PRODUCTION AND CONSUMPTION 

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UOIT, 2004. Geothermal Solution at UOIT, Internal Report, 18 November, Oshawa... 

Giggenbach, W. F., 1988, Geothermal solute equilibria, derivation of Na-K-Mg-Ca geoindicators. Geochimica et Cosmochimica Acta 52,2749-2765. 

Brine is a geothermal solution containing appreciable concentrations of sodium chloride or other salts. The chemical composition including the salinity of geothermal fluids varies greatly from one reservoir to another. Variations in chemistry and salinity affect the design, maintenance, and longevity of wells and surface equipments. Recent advances in this area include ... 

In Fig. 1.59 the relationship between temperature and concentration of elements (Zn, Ba) at constant Cl concentration which is equal to that of seawater obtained by the experimental studies and analytical data on natural hydrothermal solution (geothermal water) are shown. It is seen that the concentrations of base-metal elements (Zn, Fe, Mn, Cu, Pb) and Ba increase with increasing of temperature. Concentrations of these... 

Figure 1.56. Relationship between the zinc and Cl concentration in geothermal waters and hydrothermal solution experimentally interacted with rocks (Shikazono, 1988c).

The formation of epidote, K-feldspar, prehnite, wairakite and calcite in the geothermal area is considered to be due to the loss of CO2 gas and rapid precipitation from the solution supersaturated with respect to quartz (Browne, 1978). The widespread occurrence of these minerals in the Seigoshi district seems to be consistent with the above-mentioned consideration, namely that these minerals usually occur as veinlets rather than the replacements of original minerals and filling amygdule. In particular, many veinlets of epidote, prehnite and wairakite are found near the Au-Ag-quartz veins. 

Bird, D.K. and Helgeson, H.C. (1981) Chemical interaction of aqueous solution with epidote-feldspar mineral assemblages in geologic systems II, Equilibrium constraints in metamorphic/geothermal processes. Am. J. Set, 281, 576-614. 

Bird, D.K. and Norton, D.L. (1981) Theoretical prediction of phase relations among aqueous solutions and minerals Salton Sea geothermal system. Geochim. Cosmochim. Acta, 45, 1479-1494. 

Walshe, J.L. (1986) A six-component chlorite solid solution model and the conditions of chlorite formation in hydrothermal and geothermal systems. Econ. Geol, 81, 681-703. 

Previous studies clearly indicated that the chemical compositions of geothermal waters are intimately related both to the hydrothermal alteration mineral assemblages of country rocks and to temperature. Shikazono (1976, 1978a) used a logarithmie cation-Cl concentration diagram to interpret the concentrations of alkali and alkaline earth elements and pH of geothermal waters based on thermochemical equilibrium between hydrothermal solution and alteration minerals. 

Fig. 2.3. Relation between the K+ and CI concentration of geothermal waters and inclusion fluids. The solid line defines the equilibrium condition between the solution and the assemblage albite-K-feldspar at 250°C. For symbols used, see caption to Fig. 2.2. (Shikazono, 1978a).

The Na/Li ratio of geothermal waters decreases with increasing temperature and has been used as a geothermometer (Fig. 2.10) (Fouillac and Michard, 1981), suggesting that this ratio is controlled by feldspar-solution equilibrium (Shikazono, 1978a). 

The Okuaizu geothermal system is characterized by high temperatures (maximum 340°C), high salinity (about 2 wt% total dissolved solids (TDS)) and large amounts of non-condensable gases (1 wt% CO2 and 200 ppm H2S). The pH of the hydrothermal solution measured at 25°C is 6.44 (Table 2.6). However, the pH of the original fluid in the reservoir is computed to be 4.05. This pH as well as alkali and alkali earth element concentrations are plotted near the equilibrium curve of albite, K-mica, anhydrite and calcite (Fig. 2.19) (Seki, 1991). 

Chiba, H. (1991) Attainment of solution and gas equilibrium in Japanese geothermal sy.stems. Geochem. J., 25, 335-355. 

At the convergent plate boundaries, CO2 degasses not only from back-arc basins by hydrothermal solutions but also from terrestrial subduction zones by volcanic gases and hydrothermal solutions. However, the studies on CO2 degassing from terrestrial subduction zones are not many. Seward and Kerrich (1996) have shown that hydrothermal CO2 flux from terrestrial geothermal system (such as Taupo volcanic zone in New Zealand) exceeds lO mol/year which is comparable to that of midoceanic ridges (Table 3.4). 

The CO2 concentrations of present-day geothermal waters in terrestrial environment have been also interpreted in terms of the interaction of hydrothermal solutions with country rocks (Giggenbach, 1981 Shikazono, 1978,1985). For example, as noted in section 2.4.3, Shikazono (1985) estimated /CO2 for epithermal Au-Ag and base-metal vein-type deposits in Japan which formed in terrestrial environments at Miocene-Pliocene age and showed that fco2 controlled by the alteration minerals (Fig. 3.6). Estimated /coi" temperature range for epithermal Cu-Pb-Zn vein-type deposits are clearly similar to those for the Kuroko and back-arc deposits in which base metals (Cu, Pb, Zn) are concentrated. 

Teeuu, D. and Hesselink, F.T. "Power-Law Flow and Hydrodynamic Behavior of Biopolymer Solutions In Porous Media," SPE paper 8982, 1980 SPE Fifth International Symposium on Oilfield and Geothermal Chemistry, Stanford, May 28 30. 

Celik, M.S., Ananthapadmanabhan, K.P., and Somasundaran, P. "Precipitation/Redissolution Phenomena in Sulfonate/AlCl, Solutions," SPE paper 11796, 1983 SPE International Symposium on Oilfield and Geothermal Chemistry, Denver, June 1-3. 

Cuprasol Also called EIC. A process for removing hydrogen sulfide and ammonia from geothermal steam by scrubbing with an aqueous solution of copper sulfate. The resulting copper sulfide slurry is oxidized with air, and the copper sulfate re-used. The sulfur is recovered as ammonium sulfate. Developed by the EIC Corporation, MA, and demonstrated by the Pacific Gas Electric Company at Geysers, CA, in 1979. 

The initial methodology used assumed that all excess calcite from the solution would be deposited in a predetermined volume of the geothermal pipe. This approach is conservative considering that calcite deposition is an instantaneous process. However, the literature frequently states that calcite deposition is kinetically-controlled where the process of deposition could either be slower or faster (Sjoberg ... 

Furthermore, many of the solutions which are close to equilibrium are geothermal waters virtually all solutions less than 25°C are far from equilibrium. 

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