广东海岸带型新洲地热田水化学及海水入侵水动力特征

Hydrochemical Characteristics of Xinzhou Geothermal Field,Coastal Guangdong and the Hydrodynamic Characteristics of Seawater Intrusion in the Field

我国沿海地区是海岸带出露地热水盐度往往偏高的区域,现代海水入侵造成热水变咸需存在有利的水动力学条件,其深入研究涉及热力-水文-化学(THC)多过程耦合。通过水化学以及数值模拟试验的方法研究地热水与海水的关系,探讨新洲地热田咸水特征及其成因。结果表明:新洲地热田位于深大断裂附近,出露地热水温度高达98.40℃,地热水均为Na-Cl型,其TDS平均值为2.2g/L,具有典型的咸水特征,并利用离子比例系数初步分析了地热水与海水的混合作用;利用数值模拟试验分析了海水入侵的水动力特征,并据此提出新洲地热田海水入侵水动力的新概念,即地热水由于浮力的驱动沿深大断裂上升,且在断裂周围形成区域上的低压漏斗,其影响可达数公里,而海水由于具有较高盐度及密度,其在海水区域形成具有较高静水压力的区域,为海水的入侵提供了水动力条件。该研究结果可为海岸型地热田海水入侵以及地壳深部高温高压状态研究提供参考。

The salinity of the geothermal water that exposes in the coastal zone of China is often high. Favorable hy- drodynamic condition is the prerequisite to the salification of geothermal water caused by modern seawater intru- sion. This paper applies Thermal-Hydrology-Chemical （THC） coupling process to making an intensive study of the theory. The paper applies the hydrochemistry method and numerical experiments to studying the relationship be- tween geothermal water and sea water and to discussing the cause mechanism of saltwater in Xinzhou geothermal field. Xinzhou geothermal field is located near a deep fault and the temperature of the geothermal water can reach 98.40~C, the geothermal wateris C1-Na type and the average TDS is 2.2 g/L, which are the characteristics of typical saline water. The paper calculates the ion ratios to preliminarily analyze the mixing effect of geothermal water and seawater, and applies numerical simulation method to studying the hydrodynamic condition of seawater intrusion. Accordingly,the paper proposes a new concept of the seawater intrusion hydrodynamics in Xinzhou geothermal field. The geothermal water rises along the deep fault due to buoyancy and forms a low pressure funnel which could reach out for several kilometers around the fault zone. In addition, seawater of high density forms high pressure, which provides dynamic condition of seawater intrusion. The paper provides reference for the researches of the sea-water intrusion of coastal geothermal fields and the high temperature and high pressure condition of deep crust.