对关中盆地腹部深层地下热水δ^(18)O富集主控因素的再认识

A re-recognition of the main controlling factors for δ^(18)O enrichment in deep geothermal water of Guanzhong Basin

开展关中盆地腹部深层地下热水起源成因的研究,对推动研究区地下热水的可持续开发利用意义重大。中国大多数地下热水赋存地区的热水样点与现代循环水的关系密切,多属循环型热水,而关中盆地深层地下热水却远离大气降水线,δ^(18)O漂移显著,对此,国内外学者专家对引起关中盆地地下热水δ^(18)O富集的主要因素有不同的认识。应用同位素水文地球化学方法结合关中盆地地质构造演化,对关中盆地不同构造单元深层地下热水δ^(18)O富集的主控因素进行探索性研究。研究结果表明,影响关中盆地深层地热水δ^(18)O富集的因素是多元的,因热储环境开发度而异,在较封闭的热储条件下,其主控因素是水岩反应。热储蒸发实验的结果表明,深层地热水在进入地层前作为补给水源时,存在一定程度的蒸发作用,入渗后进入较封闭热储环境时则主要受控于水岩作用的影响,且受水岩反应的影响程度为固市凹陷>咸礼断阶东>咸礼断阶西及西安凹陷。

The research on the origin of deep geothermal water in Guanzhong Basin has a great significance for promoting the sustainable development and utilization of geothermal water.Deep geothermal water,which is circulating geothermal water,is intimately related to modern circulating water in most regions of China,About this phenomenon,experts both in China and abroad have different opinions concerning the main factors for the enrichment of theδ18O in the deep geothermal water in Guanzhong Basin.In this paper,the authors combined tectonic evolution and isotope geochemistry approaches to explore the main factors for the enrichment ofδ18O in different deep tectonic units in Guanzhong Basin.The results show the factors are diverse,because of the difference of thermal storage circumstance exploitation level,and the main factor is the water-rock interaction under relatively closed geothermal reservoir condition.The underground water evaporation experiments show that,before the geothermal water as the source pours into the geothermal reservoir,there usually occurs some degrees of evaporation.When the supplied water comes into the geothermal reservoir,the enrichment ofδ18O has been affected by water-rock reaction,and the influence degree of water-rock interaction in different tectonic units is in order of Gushi depression>the east of Xianli terrace>Xi'an depression and the west of Xianli terrace.