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我国具有非常丰富的碳酸泉水资源,不仅有低温的,也有对科学研究具有重要意义的高温碳酸泉水[1]。碳酸泉具有非常重要的研究价值,不仅在饮用、洗浴等方面具有特殊的医疗保健价值,同时碳酸泉出露带分布与地震活动性关系密不可分,可为地震方面的研究提供参考[2]。碳酸泉含有大量游离CO2,导致水的密度降低、流动性增强,地下热流流动加剧。CO2在上升过程中把深部热量带到地表,会影响当地的地热分布。刘尚任[3]在前人研究数据基础上总结出广东碳酸泉水中游离CO2由岩石热变质作用产生,其出露点地下存在能够汇集和储存碳酸泉水的储集构造,会降低泉水温度。张卫民等[4]利用同位素分析方法,探讨了赣南地区碳酸温泉水、气同位素组成及成因,得出当地碳酸温泉水源于大气降水补给,气源于深部的结论。李静荣等[5]利用地质分析、水化学分析、同位素分析结合的方法,探讨了河源断裂带周边出露碳酸泉的形成机制,分析出碳酸泉水中游离CO2为深部围岩在高温高压作用下热变质所释放,龙川、黎咀盆地盖层因被断裂带切割而使贮集的CO2沿河源深大断裂上升,途中与地下水混合。当前国内外对于碳酸泉的研究较少,且多停留在其医疗价值及与地震之间的联系[6-7],对碳酸泉的形成机理也只做总结性分析,缺少典型数据模型支撑。
广东处于亚欧板块东南边缘,长期受到印度洋板块、太平洋板块和亚欧板块的相对俯冲影响,省内深大断裂发育良好。据研究表明,河源深大断裂带附近有多处碳酸泉分布,其中一处位于龙川县老隆镇泰华城。广东省地球物理探矿大队于2011年在此碳酸泉出露区域开展以深部热储埋藏及深孔碳酸地热水为主的地质与物探基础调查工作,共布设8处钻探。其中代表性的3500.00 m钻探(CSK1)旨在确定井孔温度场与盖层岩性及物性的关系,揭示在水循环条件下热流传输的机理和找出主导控制因素条件。本研究将从深孔碳酸地热水的水化学特征出发,逐步深入阐述其热储和循环特征,为今后碳酸泉形成机理的研究提供科学依据,促进全面认识碳酸泉形成过程,这对未来水文循环、深部流体、地震先兆的研究均有参考意义。
广东省龙川县深孔碳酸地热水的水化学特征
Hydrochemical characteristics of carbonated geothermal water from deep borehole in Longchuan County, Guangdong Province
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摘要: 碳酸泉以富含游离CO2为特征,主要分布在深大断裂带和地震活动带上。通过针对广东省龙川县3个不同深度的钻孔数据对碳酸地热水的水文地球化学特征进行研究,揭示其水化学组分主要为碳酸盐矿物溶解控制,游离CO2运移过程中强化了水的溶滤作用。Na-K-Mg三角图解和PHREEQC计算表明水-岩作用处于不平衡状态,通过石英温标、玉髓温标及多矿物水-岩平衡估算了地热水的热储温度为60—102 ℃,循环深度为1692—3548 m。该水化学特征成果可以进一步讨论碳酸泉的形成机理,反映气体在深部地热流和温度剖面中的作用,为研究深部流体对地震的同震响应及地热资源开发提供依据。Abstract: Carbonated springs are characterized by the enrichment of free CO2, which are mainly distributed in deep fault zones and seismic active belts. Based on the data from three boreholes at different depths in Longchuan County, Guangdong Province, the hydrogeochemical characteristics of carbonated geothermal waters have been studied in our work. The results reveal that the chemical compositions of the water samples are mainly controlled by the dissolution of carbonate minerals, and the migration process of free CO2 strengthens the leaching effect of water. The Na-K-Mg triangle diagram and PHREEQC calculations show that the water-rock interaction is in an unbalanced state. According to the quartz, chalcedony geothermometer results as well as multimineral water-rock balance calculations, the reservoir temperatures and the circulation depths in the study area are estimated to be 60—102 ℃ and 1692—3548 m, respectively. The study on the hydrochemical characteristics of geothermal waters can further improve our understanding of the formation mechanism of carbonated springs, which not only provides new insight into the role of gas in deep geothermal flow and temperature profile, but also makes contributions to the study of the coseismic response of deep fluids to earthquakes and the future exploitation of geothermal resources.
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Key words:
- carbonated spring /
- hydrochemistry /
- geothermal water /
- fault zone /
- water-rock interaction
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表 1 水样的物理化学特征参数
Table 1. Physicochemical properties of the water samples
编号
No.取样日期
DatepH T/℃ TDS/
(mg·L−1)K+/
(mg·L−1)Na+/
(mg·L−1)Ca2+/
(mg·L−1)Mg2+/
(mg·L−1)HCO3-/
(mg·L−1)Cl-/
(mg·L−1)SO42-/
(mg·L−1)F-/
(mg·L−1)NO3−/
(mg·L−1)Si/
(mg·L−1)CO2/
(mg·L−1)ZK1-1 2011.11.29 7.10 25.80 6840.52 123.61 1214.40 378.53 95.95 4694.51 39.00 252.53 2.49 0.31 19.32 806.78 ZK1-2 2011.12.29 7.07 26.30 7121.10 151.12 1237.00 356.23 132.64 4858.34 34.91 306.39 2.68 0.59 20.47 1000.82 ZK1-3 2018.08.27 7.07 27.00 5847.22 107.40 1150.00 199.48 86.02 3959.53 36.12 258.15 2.52 0.00 22.39 545.82 ZK2-1 2011.11.29 6.86 25.30 839.85 5.27 83.13 95.83 20.35 520.01 8.86 40.89 0.38 37.06 13.17 105.19 ZK2-2 2011.12.29 6.74 25.80 1309.24 11.56 96.30 170.02 33.16 861.51 5.37 63.43 0.41 31.93 16.73 502.45 ZK2-3 2012.02.05 6.99 25.70 840.34 4.12 66.71 113.35 19.65 515.96 8.06 48.37 0.22 35.08 13.54 106.21 CSK1 2018.08.27 7.34 48.00 7480.75 135.00 1830.00 97.51 41.67 4716.48 79.05 509.20 5.44 0.00 30.93 396.97 表 2 研究区水样部分矿物饱和指数值(SI)a
Table 2. Partial mineral saturation index values of water samples in the study areaa
编号
No.硬石膏
Anhydrite文石
Aragonite方解石
Calcite白云石
Dolomite萤石
Fluorite岩盐
Halite石膏
Gypsum天青石
CelestiteSiO2 玉髓
ChalcedonyZK1-1 −1.46 1.35 1.50 2.77 −0.10 −6.03 −1.17 −1.51 −0.77 0.06 ZK1-2 −1.42 1.31 1.45 2.85 −0.10 −6.08 −1.13 −1.33 −0.75 0.08 ZK1-3 −1.64 1.03 1.17 2.36 −0.32 −6.08 −1.36 −1.65 −0.72 0.11 ZK2-1 −2.26 −0.05 0.10 −0.13 −1.82 −7.72 −1.96 −1.68 −0.95 −0.11 ZK2-2 −1.94 0.24 0.38 0.42 −1.63 −7.90 −1.65 −1.30 −0.85 −0.01 ZK2-3 −2.12 0.15 0.30 0.19 −2.22 −7.86 −1.83 −1.48 −0.94 −0.10 CSK1 −1.55 1.24 1.37 2.89 −0.28 −5.58 −1.49 −1.39 −0.74 0.03 注:a.水化学数据见表1. Note: a. Hydrochemical data are shown in Table 1. 表 3 采样点热储温度估算
Table 3. Estimation of Heat Storage temperature at sampling points
编号
No.水样温度/℃
Water samples
temperature地温计法-石英-无蒸汽损失/℃
Geothermometer method-Quartz-no
steam loss地温计法-玉髓/℃
Geothermometer
method-Chalcedony矿物平衡法/℃
Multiple mineral
equilibrium methodZK1-1 25.80 93.22 64.55 67.38 ZK1-2 26.30 95.80 67.13 66.55 ZK1-3 27.00 99.89 71.23 69.00 ZK2-1 25.30 76.90 48.29 70.91 ZK2-2 25.80 86.91 58.25 66.98 ZK2-3 25.70 78.04 49.42 59.66 CSK1 48.00 115.44 86.89 102.35 -
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