Aquifer fluid modeling and assessment of mineral-gas-liquid equilibria in the Námafjall geothermal system, NE-Iceland /
- 出版日期：2012.
- 出版者：United Nations University, Geothermal Training Programme,
- 页数：ix, 57 p. :
- 出版地：Reykjavík :
- 第一责任说明：by Sylvia Joan Malimo.
- 尺寸：24 cm.
- 分类号：a485.4
- ISBN：978-9979-68-322-3(pbk.) :
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02h0044519 20131212165900.0 131211s2012 ic ab frbm |000|||eng | 978-9979-68-322-3(pbk.) : CNY100.00 NGL NGL NGL 333.88 a485.4 Malimo, Sylvia Joan. Aquifer fluid modeling and assessment of mineral-gas-liquid equilibria in the Námafjall geothermal system, NE-Iceland / by Sylvia Joan Malimo. Reykjavík : United Nations University, Geothermal Training Programme, 2012. ix, 57 p. : ill., maps ; 24 cm. Reports, 1670-7427 ; 2012/3 MSc thesis. Includes bibliographic reference. This study presents a geochemical evaluation of the Námafjall high-temperature geothermal field with respect to the chemical and physical processes that account for the fluid concentrations of volatile and non-volatile components, and the mineral assemblages controlling equilibrium in the aquifer. Aquifer fluid compositions and aqueous species distribution, for 25 samples collected from 7 wet-steam well discharges, were calculated from water- and steam-phase analyses and discharge enthalpies using the WATCH 2.1 speciation program according to the phase segregation model. Phase segregation pressures calculated at ~80% volume fraction of the flowing vapor are selected in view of the fact that liquid saturation at this pressures relate to residual liquid saturation of 0.2. The modelled aquifer fluid compositions were used to assess how closely equilibrium is approached between solution and various minerals. H2S and H2 concentrations were used to evaluate the presence of equilibrium vapor fraction in the initial aquifer fluid, calculated as 0-3.9% by weight with a field average of 0.79% by weight.At inferred Námafjall aquifer temperatures (200-300°C), the concentration of H2S in the initial aquifer fluids is somewhat higher than predicted at equilibrium with hydrothermal mineral assemblage consisting of pyrite, pyrrhotite, prehnite and epidote, while concentration of H2 closely approaches equilibrium for the excess enthalpy wells unlike for the liquid enthalpy wells. With respect to CO2 the calculated chemical compositions of initial aquifer fluid show a close approach to equilibrium (for liquid enthalpy wells) but lower than equilibrium for the excess enthalpy wells with the hydrothermal alteration minerals clinozoisite, calcite, quartz and prehnite. The shallower aquifer at Námafjall are higher in gas (H2S, H2, CO2 and N2) indicating that gaseous steam from deeper aquifers has condensed in the shallower ones signifying that they are, at least partly, steam-heated. The main uncertainty involved in calculating mineral saturation indices, particularly in the case of excess enthalpy well discharges, lies in the model adopted to calculate the aquifer water composition and its aqueous species distribution and in the quality of the thermodynamic data on the aqueous species and the minerals especially those that involve Fe-bearing species. In the deep aquifers, chemical equilibrium has been rather closely approached between dissolved solids, H2S and H2 on one hand and hydrothermal minerals on the other. Geothermal resources Iceland. Reports / UNU Geothermal Training Programme ; 2012, no.3. aCN b010001 NGL P 485.066 R29 v2012/3 ; h1 ; rCNY100.00 gljx1305