Geothermal driving force: A new additional non-gravity action driving the migration of geothermal water in the Xinzhou geothermal field of Yangjiang, Guangdong
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摘要: Tóth总结提出的"嵌套式多级次水流系统",和张人权等学者归纳总结的重力驱动地下水流系统理论,是地下水运移的重要理论基础。地下水的流动可能受到重力势、压实势、构造挤压力共同作用。然而,在对流型水热系统中发现了地下水补给区位置低于排泄区的反常现象。由于温度升高导致地热水密度减小和压力增大,使得地热水的实际压力水头增大,是出现这种反常现象的物理基础。笔者定义这种额外增大的压力水头为"地热驱动力",分析其大小与地热水温度、盐度、黏滞度的关系并给出量化计算方法。在广东阳江新洲地热田的研究实例中,地热驱动力的启动点位于地热水循环的最深处4.34 km,该处由温度升高产生的地热驱动力的标准水头为+351.59 m,由盐度增加产生的地热驱动力的标准水头为-2.78 m,总的地热驱动力的标准水头为+348.81 m。地热水温度越高,地热驱动力越大;盐度越大,地热驱动力越小。地热驱动力的额外加持作用可以加快水热系统中地下水的循环。Abstract: The "nested multilevel flow system" summarized by Tóth and the gravity driven groundwater flow system theory summarized by Zhang Renquan et al are the important theoretical basis for groundwater migration.Groundwater flow may be affected by gravitational potential, compaction potential and tectonic compression force.However, the anomalous phenomenon that the groundwater recharge area is lower than the groundwater drainage area is found in the convective hydrothermal system.As the temperature rises, the density of geothermal water decreases and the pressure increases, and the actual pressure head of geothermal water increases, which is the physical basis for this abnormal phenomenon.This paper defines the additional pressure head as "geothermal driving force", which is related to the temperature, salinity and viscosity of geothermal water.And we propose a quantitative calculation method.In the case of Xinzhou geothermal field in Yangjiang, Guangdong Province, the starting point of the geothermal driving force is located at the deepest part of the geothermal water cycle of 4.34 km, where the standard head of the geothermal driving force generated by temperature rise is +351.59 m, and the standard head of the geothermal driving force generated by salinity increase is -2.78 m, and the standard head of total geothermal driving force is +348.81 m.The higher the geothermal water temperature is, the greater the geothermal driving force is.The greater the salinity, the smaller the geothermal driving force.The additional supporting effect of geothermal driving force can accelerate the circulation of groundwater in hydrothermal system.
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Key words:
- geothermal driving force /
- temperature /
- salinity /
- geothermal water /
- Xinzhou of Yangjiang
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图 1 我国主要水热系统分类示意图(据文献[19]修改)
Figure 1. Classification of main hydrothermal systems in China
图 2 常温和对流型水热系统中地下水密度与水头变化示意图(据文献[14]修改)
Figure 2. Changes in density and head of groundwater in normal temperature and convective hydrothermal systems
图 4 新洲地热田成因模式图[16]
Figure 4. Conceptual model of hydrothermal system in Xinzhou geothermal field
表 1 新洲地热田主要水化学及同位素数据[16]
Table 1. Main data of water chemistry and isotope of Xinzhou geothermal field
样品编号 类型 深度/m 温度/℃ ρ(TDS)/(mg·L-1) ρ(SiO2)/(mg·L-1) 热储温度/℃ 热储深度/km 14C年龄/ka TW1 热井 209.25 92.7 2 840 123.47 140 3.88 3.33 TW2 热井 350.86 94.0 2 804 133.74 148 4.14 3.27 TW3 热井 298.92 97.5 2 788 153.75 154 4.34 7.54 TW4 热井 399.31 98.0 2 753 153.75 153 4.31 7.59 TW5 热井 299.62 87.3 2 521 121.14 144 4.01 5.88 TS1 温泉 / 87.0 1 957 114.83 138 3.81 5.85 TS2 温泉 / 95.0 2 276 103.57 132 3.62 18.99 TS3 温泉 / 90.0 1 980 89.41 123 3.32 11.85 TS4 温泉 / 67.0 1 996 101.36 125 3.38 17.81 TS5 温泉 / 74.5 1 736 107.11 134 3.68 13.74 TS6 温泉 / 84.5 1 767 88.52 121 3.25 18.85 CS1 冷泉 / 28.5 158 9.08 / / / CS2 冷泉 / 26.3 142.83 8.85 / / / CS3 冷泉 / 27.9 177.52 7.34 / / / CS4 冷泉 / 31.0 159.97 5.82 / / / CS5 冷泉 / 26.2 157.53 16.13 / / / CS6 冷泉 / 32.6 94.89 14.33 / / / 表 2 新洲地热田温度变化下压力水头的变化
Table 2. Changes of pressure head under temperature changes in Xinzhou geothermal field
深度/m 标准密度/ (kg·m-3) 该深度标准压力水头/m 地热水温度/℃ 该温度下的密度/ (kg·m-3) 升温后实际压力水头/m 升温产生的额外标准水头差/m 0 1 000 0 83.00 965.14 0 0 311.59 311.59 93.90 957.75 325.34 +13.75 682.95 682.95 106.90 948.55 713.08 +30.13 4 338.72 4 338.72 137.45 925.04 4 690.31 +351.59 表 3 新洲地热田盐度变化下压力水头的变化
Table 3. Changes of pressure head under salinity changes in Xinzhou geothermal field
深度/m 标准密度/ (kg·m-3) 该深度标准压力水头/m ρ(TDS)/ (mg·L-1) 该盐度下的密度/ (g·L-1) 该盐度下实际压力水头/m 盐度产生的额外标准水头差/m 0 1 000 0 1 952.00 1 001.95 0 0 311.59 311.59 2 741.20 1 002.74 310.74 - 0.85 682.95 682.95 3 681.78 1 003.68 680.45 - 2.51 4 338.72 4 338.72 643.55 1 000.64 4 335.94 - 2.78 表 4 新洲地热田地热驱动力产生的额外压力水头
Table 4. Additional pressure head generated by the geothermal driving force of the Xinzhou geothermal field
深度/m 该深度标准压力水头/m 升温产生的额外标准水头差/m 盐度产生的额外标准水头差/m 地热驱动力产生的额外压力水头/m 该深度实际压力水头/m 0 0 0 0 0 0 311.59 311.59 +13.75 - 0.85 +12.90 324.49 682.95 682.95 +30.13 - 2.51 +27.62 710.57 4 338.72 4 338.72 +351.59 - 2.78 +348.81 4 687.53 -
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