鲜水河断裂带地热水化学特征及结垢趋势分析

Geothermal water chemical characteristics and scaling analysis of Xianshuihe fault zone

关键词:  鲜水河断裂带  地热水水化学  补给来源  热储温度  地热水结垢

Key words:  Xianshuihe fault zone  hydrochemistry of geothermal water  recharge source  reservoir temperature  scaling of geothermal water

摘要:

地热资源作为潜力巨大的清洁能源，大力开发地热资源是我国实现双碳目标的重要路径。川西鲜水河断裂带地热资源丰富，但地热结垢成为了地热资源开发利用中的主要问题之一。为进一步查明地热资源的赋存状态和结垢趋势特征，本文以鲜水河断裂带上的磨西、榆林宫、二道桥、中谷、八美和道孚地热区为研究区，采用水化学分析、氢氧同位素、热储温度估算和结垢趋势特征分析等方法，开展了鲜水河断裂带地热水水化学及结垢趋势特征研究。结果表明：地热水的水化学类型主要为Na-HCO₃、Ca-HCO₃、Ca·Na-HCO₃和Na-Cl·HCO₃型；地热水主要来源于大气降水的补给且氧漂移现象明显；地热水均未达到完全的水-岩平衡状态，混合冷水后的浅部热储温度为61℃～172℃，深部初始热储温度平均值为183℃～284℃，冷水混合比例平均值为77%～86%；指数分析法和饱和指数判别法得出以上地热区均有可能形成碳酸盐结垢，硅酸盐结垢仅可能会形成于少数SiO₂含量异常高的区域，而硫酸盐结垢几乎不形成；依据硅-焓模型估算的冷水混合比例重构得出深层储层流体组分，计算得出二道桥地区的碳酸盐结垢程度是最严重的，主要是因为该区的热储岩性为碳酸盐岩，以及热储温度能促进CaCO₃沉淀。对于除垢和预防，可以采用机械拆除、控制CO₂分压、控制溶液的pH值和使用化学添加剂（阻垢剂）等。研究成果可为鲜水河断裂带及川西地热资源的可持续开发利用提供理论依据。

Abstract:

Geothermal resources have great potential as clean energy, and can be used to achieve the goal of carbon peaking and carbon neutrality. The Xianshuihe fault zone in western Sichuan is rich in geothermal resources, but geothermal scaling has become one of the main problems in the development and utilization of geothermal resources. In order to further identify the occurrence state and scaling trend characteristics of geothermal resources, this paper takes the six areas of Moxi, Yulingong, Erdaoqiao, Zhonggu, Bamei and Daofu on the Xianshuihe fault zone as the research area, and uses water chemistry analysis, hydrogen and oxygen isotopes, heat storage temperature estimation and scaling trend characteristics analysis to carry out the geothermal water hydrochemistry and scaling trend characteristics of the Xianshuihe fault zone. The results show that the hydrochemical types of geothermal water are mainly Na-HCO₃, Ca-HCO₃, Ca·Na-HCO₃ and Na-Cl·HCO₃; Geothermal water mainly comes from the supply of atmospheric precipitation and oxygen drift occurs in most areas; The geothermal water has not reached the complete water-rock equilibrium state, and the shallow geothermal reservoir temperature is 61℃～172℃. The average temperature of deep thermal reservoir is 183℃ to 283℃, and the average cold water mixing ratio is 77% to 86%; The exponential analysis method and the saturation index discrimination method show that carbonate scaling may occur in the all above geothermal areas. Silicate scaling may only occur in several areas with abnormally high SiO₂ content, while sulfate scaling almost does not occur. According to the cold water mixing ratio estimated by the silicon-enthalpy model, the fluid composition of the deep reservoir is reconstructed. Combined with the formula, it is calculated that the carbonate scaling degree in the Erdaoqiao area is the most serious, mainly because the reservoir lithology in the area is carbonate salt, and the reservoir temperature can promote the precipitation of CaCO₃. For descaling and prevention, mechanical removal, control of CO₂ partial pressure, control of solution pH, and use of chemical additives (scale inhibitors) can be used. The research results can provide a theoretical basis for the sustainable development and utilization of geothermal resources in the Xianshuihe fault zone and western Sichuan.