THEORETICAL CHEMICAL THERMOMETRY ON GEOTHERMAL WATERS: PROBLEMS AND METHODS
THEORETICAL CHEMICAL THERMOMETRY ON GEOTHERMAL WATERS: PROBLEMS AND METHODS
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DOI：
10.1016/s0016-7037(98)00037-4
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发表时间：
1998-03
影响因子：
5
通讯作者：
Z. Pang;M. Reed
中科院分区：
文献类型：
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作者：
Z. Pang;M. Reed
使用合成的地热水，我们研究铝分析的理论化学地质测温的基础上，矿物平衡的多组分化学平衡计算的误差的影响。一种名为FixAl的新方法，需要一个修改的Q/K图的建设消除了水分析缺乏铝或铝的错误分析的问题。这是可能的，迫使水与选定的含铝矿物，如微斜长石平衡。在FixAl图中，针对含铝矿物的温度绘制了修改后的Q/K值。非铝质矿物的饱和指数的绘制方法与普通Q/K图相同。除了铝浓度误差，CO2的脱气和水库水的稀释干扰计算的平衡地质温度。通过比较非铝矿物和铝矿物的曲线，然后用试错法校正CO2损失和稀释，可以在Q/K图中区分这些影响。用于演示这些方法的来自中国、冰岛和美国的地热沃茨水示例表明，铝浓度的错误很常见，有些甚至很严重。事实证明，FixAl方法对于缺乏Al分析的地热沃茨水和Al分析不正确的沃茨水的化学地质测温很有用。由FixAl方法估计的平衡温度与石英、玉髓和同位素地质温度计一致。强制平衡矿物的最佳选择取决于pH值。对于大多数中性沃茨，微斜长石和钠长石工作良好;对于更酸性的沃茨，高岭石或伊利石是很好的选择。测量的pH值在计算平衡中起着关键作用，我们发现使用的最佳pH值是报告的碳酸盐也适用的pH值。通常这是实验室pH值而不是现场pH值，但现场pH值仍然是限制CO2脱气所必需的。对80-180°C储层温度范围内的许多沃茨的计算表明，矿物-水平衡可能几乎总是实现的，但被近地表环境中CO2稀释或脱气的短时间尺度过程所掩盖。
Using a synthetic geothermal water, we examine the effect of errors in Al analyses on theoretical chemical geothermometry based on multicomponent chemical equilibrium calculations of mineral equilibria. A new approach named FixAl that entails the construction of a modified Q/K graph eliminates problems with water analyses lacking Al or with erroneous analyses of Al. This is made possible by forcing the water to be at equilibrium with a selected Al-bearing mineral, such as microcline. In a FixAl graph, a modified Q/K value is plotted against temperature for Al-bearing minerals. Saturation indices of nonaluminous minerals are plotted in the same way as in an ordinary Q/K graph. In addition to Al concentration errors, degassing of CO2and dilution of reservoir water interfere with computed equilibrium geothermometry. These effects can be distinguished in a Q/K graph by comparing curves for nonaluminous minerals to those of aluminous minerals then correcting for CO2loss and dilution by a trial and error method. Example geothermal waters from China, Iceland, and the USA that are used to demonstrate the methods show that errors in Al concentrations are common, and some are severe. The FixAl approach has proved useful for chemical geothermometry for geothermal waters lacking Al analysis and for waters with an incorrect Al analysis. The equilibrium temperatures estimated by the FixAl approach agree well with quartz, chalcedony, and isotopic geothermometers. The best choice of mineral for forced equilibrium depends on pH. For most neutral pH waters, microcline and albite work well; for more acidic waters, kaolinite or illite are good choices. Measured pH plays a critical role in computed equilibria, and we find that the best pH to use is the one to which the reported carbonate also applies. Commonly this is the laboratory pH instead of field pH, but the field pH is still necessary to constrain CO2degassing. Calculations on numerous waters in the 80–180°C reservoir temperature range indicate that mineral-aqueous equilibrium is probably nearly always achieved, but is obscured by short time-scale processes of dilution or degassing of CO2in the near-surface environment.