Research progress on stable isotopes of hydrogen and oxygen and application on the geothermal fluid migration and evolution

Geothermal fluid, as an important component of groundwater circulation system, has strong economic value and social significance. The stable isotopes of hydrogen and oxygen are the important information indicators for understanding the water cycle system. Their composition characteristics can reveal the regular changes in the migration and evolution process of geothermal fluids in the region. They play an important role in understanding the sources of geothermal fluid supply in the region, recognizing the geothermal water cycle path, and providing theoretical support for the rational development and utilization of geothermal resources, which is of great significance. At present, using abundance, isotope ratio（R value）, thousand point deviation value（δ value）, d-excess and ¹⁷O-excess to represent the composition characteristics of stable isotopes of hydrogen and oxygen. By comparing with reference materials, analyze the variation patterns and trends of stable isotopes of hydrogen and oxygen, so as to judge the regional evolution and differentiation characteristics of stable isotopes of hydrogen and oxygen in marine water, atmospheric water vapor, precipitation, river, lake water and groundwater circulation system, and then analyze the temperature, humidity and geological conditions of the water circulation system; clarify the source and proportion of its supply; determine factors such as water evaporation and retention time within the system. However, as a part of the groundwater circulation system, there are still shortcomings in the research on the stable isotopes of hydrogen and oxygen in geothermal fluids. It is necessary to strengthen the research on the stable isotopes of hydrogen and oxygen in geothermal fluids, recognize their relationship with other water circulation systems in the region, and pay attention to introducing new parameters, applying new methods, and persistently conducting long-term and continuous monitoring research.