川西地下流体观测井水文地球化学特征

Hydrogeochemical Characteristics of Groundwater in Seismic Observation Wells in the Western Sichuan

开展地下流体观测井的水文地球化学研究,可以为地下流体前兆异常判断提供有力的支持。为确定四川西部地区主要观测井的水文地球化学背景,以龙门山断裂带、安宁河-则木河断裂带、华蓥山断裂带南段及其分支断裂上的19口地震观测井为研究对象,采集井水进行了水化学组分和氢、氧同位素测试。水化学组分分析结果显示,水样可划分为11种水化学类型,总体受含水层岩性控制,与断裂带分布关系不大,无明显的空间分布特征;氢、氧同位素测试表明,井水的δD和δ18O指示井水来源于大气降水,并与地表水的水力联系密切;水-岩化学平衡反应特征表明观测井SC-3和SC-4的地下水循环时间长,水-岩作用程度高,为完全平衡水。其他观测井的井水则为部分平衡水或未成熟水,表现出地下水滞留时间短、水-岩反应程度较弱等特点。

The hydrogeochemical study of groundwater in seismic observation wells can provide strong support for judging seismic-chemical anomalies of the groundwater.In order to discuss the hydrogeochemical background of seismic observation wells in the western Sichuan,the chemical compositions and H and O isotopes of groundwater samples collected from 19 seismic observation wells in areas of the Longmenshan fault,the Anninghe-Zumuhe fault and the southern segment of the Huayingshan fault have been analyzed in this paper.The results indicate that the water samples can be classified into 11 chemical types,which are controlled by the lithology of aquifer,with little relationship to the fault zone and no obvious spatial distribution feature.The isotopic data(δD andδ18O)indicate that these groundwater samples were originated from the meteoric water and are closely related to the surface water in hydraulic connection.The analysis of the characteristic of water-rock reaction reveal that the groundwater in SC-03 and SC-04 wells are characterized with long circulation time,strong water-rock reaction,and high TDS contents,meaning the completely equilibrated water.Other water samples are classified as partial equilibrated or immature water,which are characterized with short circulation time and weak water-rock reaction.