| 摘要: |
| 地球化学方法是了解地热系统特点、变化及起源的重要手段，合理开发利用地热资源的前提。基于咸阳地热田XY1地热井1999年与2017年两期水质资料、多年水温变化资料，参考其他学者在研究区取得的研究成果，综合分析了该热水井及区域地热流体地球化学因子的变化特征。根据地热水δD、δ18O、14C同位素分析，探讨了该地区地热水的起源及其同位素水文特征。结果表明：该热水井水温变化不大，水-岩平衡状态未改变，大部分离子组分浓度呈上升趋势，水质变差。水化学类型未改变，为Cl-Na型，其中多种水化学组分浓度达到一定标准，可作为医疗热矿水开发利用。研究区热储层以消耗静态储量为主，无现代降水补给。该井地下热水属于第四纪末次冰期北山山区海拔1200 m大气降水入渗成因，为混入古溶滤水的残存沉积水。建议生产过程中应采取地热水回灌措施，使地热资源开发具有可持续性。 |
| 关键词: 咸阳地热田 地热水 同位素 水化学特征 |
| DOI：10.7515/JEE202005 |
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| 基金项目:黄土与第四纪地质国家重点实验室开放基金（SKLLQG1933）；中央高校基本科研业务费资助项目（自然科学类）（300102298203）；陕西省自然科学基础研究计划资助项目（2017JM4018） |
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| Analysis of geochemical characteristics of the geothermal water in a typical geothermal well in Xianyang area |
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DENG Ruolan, YANG Yinke, LI Qiang, YU Miao
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1. Key Laboratory of Subsurface Hydrology and Ecological Effects in Arid Region, School of Water and Environment, Chang’an University, Xi’an 710054, China
2. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
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| Abstract: |
| Background, aim, and scope Geothermal water resources are the products of the interaction between geothermal energy, groundwater and rocks and minerals, and can be used as a heat source, water source and mineral resources, which is a new type of green energy. Geothermal water resources have obvious advantages in relieving energy pressure, adjusting energy structure and improving environmental quality, but they are not inexhaustible. The distribution of geothermal wells in urban areas of Xianyang is dense, and the amount of geothermal water extraction is large, but the long-term extraction of geothermal heat has caused the supply of groundwater with lower temperature or high-temperature thermal fluid at depth, thus causing changes in the chemical characteristics of geothermal fluid. The study of geothermal well hot water geothermal system changes and causal characteristics has become an inevitable requirement for the efficient and reasonable use of geothermal water resources in Xianyang region. Materials and methods In this paper, the sampling site was selected as 185 coalfield geological team (34°22′N, 180°44′E), Zhouling Village, Weicheng District, Xianyang City, Shaanxi Province. In 1999 and 2017, water chemistry samples were collected in the region to collect hot water samples. In this paper, the water quality data of 1999 and 2017 and the data of multi-year water temperature changes were integrated, and the research results of other scholars in the research area were taken into consideration to study the change trend of the chemical composition, water temperature and water-rock balance of geothermal water. In addition, the characteristics of geochemical factors of the hot water well and regional geothermal fluid were also comprehensively analyzed. According to the research and analysis of δD, δ18O, 14C isotopes of geothermal water, the origin of geothermal water and its isotopic hydrological characteristics in this region are revealed and discussed. It is hoped that this paper will provide scientific basis for the efficient utilization, management and protection of geothermal resources in this region as well as the prospect of geothermal industry development. Results According to the stable hydrogen and oxygen isotopes, the geothermal water supply elevation was calculated to be 1200 m. From the 14C test age of 20251 a, it can be seen that XY1 well geothermal water belongs to the cause of precipitation infiltration in Beishan Mountain Area in the last glacial period of the Quaternary. Well XY1 was mainly used to exploit the thermal reservoir of Bahe formation in Lantian, with no change in the chemical type of geothermal water and the dynamic of water-rock equilibrium, and little change in water temperature. There was no shallow low temperature water supply in the thermal reservoir, nor deep high temperature water supply. Discussion Based on the correlation between δ18O andδD values in the geothermal water of the well and the chemical composition of the groundwater, it can be inferred that the thermal reservoir fluid is the residual sedimentary water mixed with the ancient lixiviation water. The analysis showed that the renewable capacity of groundwater hot water in this region is relatively poor. With the consumption of static reserves as the main factor, the water level in this area decreased greatly, forming a descending funnel, which leads to the depletion of underground hot water resources and the deterioration of water quality. Geothermal wells without treatment of direct discharge will inevitably produce more serious thermal pollution of the urban environment, and the harmful chemicals contained in underground hot water can also pollute the water environment, soil environment and air environment. Therefore, it is necessary to strengthen the protection of the environment and the safety of drinking water sources during its discharge. It can only be discharged after the treatment has reached the standard, and measures such as geothermal water recharge can be taken. Conclusions The thermal reservoir in the study area mainly consumes static reserves without modern precipitation supply. The geothermal water in the well belongs to the cause of 1200 m atmospheric precipitation infiltration in the Beishan Mountain Area during the late Quaternary glacial period, which is the residual sedimentary water mixed with the ancient lixiviation water. In order to promote the experimental study of geothermal recharge, measures of geothermal water recharge should be taken in the production process. Recommendations and perspectives (1) It is necessary to further strengthen resource exploration and evaluation, and constantly revise and improve plans for the development and utilization of geothermal resources. (2) It is recommended that research be carried out on the development of medical thermal mineral water and its medical, health care and wellness effects. (3) The dynamic automatic monitoring and control system of geothermal mining can be established and improved to strengthen the chemical monitoring of geothermal fluid to understand the changes of geothermal system and strengthen management to make the development of geothermal resources sustainable. |
| Key words: geothermal field of Xianyang City geothermal water isotopes hydrochemical characteristics |
