甘肃武山地热田水化学与地热水起源

通过对武山地热田地热水和地下冷水的水化学和同位素分析,结果表明武山地热水的出露温度为18.2~42.1℃,TDS含量为238~255 mg/L,属于低矿化度的HCO3型水。相对于地下冷水,地热水有更高的S iO2、F含量,说明经历了比冷水更长的循环深度。水化学特征表明武山地热水为大气降水与岩石相互作用的初级阶段。武山冷水和地热水的同位素沿着西北大气降水线分布,由于地热水的水岩相互作用时间较长,有更低的δD和δ18O值,说明武山地热水是大气来源的。综合运用各种地热温标估算武山地热水的热储温度范围在70~106℃之间,按照甘肃东部的平均地温梯度(35℃/km),得出武山地热水循环深度为1.74~2.77 km,属于中低温地热系统。此研究为今后可持续开发武山地热水提供了科学依据。

Hydrochemistry and Origin of the Wushan Geothermal Field, Gansu

The results of the analysis of chemistry and isotope of geothermal waters and cold groundwater in Wushan geothermal field indicate that thermal waters of Wushan geothermal field have outlet temperatures of 18.2-42.1 ℃ and TDS of 238-255 mg/L, belonging to bicarbonate water of low-salinity. Compared to cold groundwater, thermal waters have higher concentration of SiO₂ and F, which indicate thermal waters have experienced deeper circulation than cold groundwater. Chemical characteristics suggest that thermal waters of Wushan are typical of the first stage of interaction between meteoric water and rock. δ¹⁸O and δD values of samples close to north-west meteoric water line of China, which shows that Wushan thermal water is of meteoric origin. Thermal water has lower δD and δ¹⁸O than cold groundwater, which suggests a relatively long subsurface circulation. The temperature of geothermal reservoir of Wushan thermal waters range from 70 to 106 ℃ estimated with various chemical geothermometer, and corresponding reservoir depth is from 1.74 to 2.77 km according to average geothermal gradient of eastern Gausu of 35℃/km, thus leading to the conclusion that Wushan thermal waters belong to low-medium geothermal resource. This study provides scientific basis for sustainable exploitation of geothermal water in Wushan geothermal field.