ISSN 1000-3665 CN 11-2202/P

    西宁盆地地热水特征及回灌结垢风险

    Characteristics of geothermal water in the Xining Basin and risk of reinjection scaling

    • 摘要: 青海西宁盆地中低温地热资源丰富,但热储地层以含黏土矿物的弱胶结砂岩为主,地热水溶解性总固体较高,回灌过程中存在显著的结垢风险。基于对西宁盆地地热成因及资源分布特征分析,采用矿物溶解度法、饱和指数法等方法对典型地热水回灌结垢趋势及风险进行了综合判断。结果表明:西宁盆地“凹中凸”构造有利于地热水在深部热储富集和增温,同时将深部溶解的大量矿物质带到西宁地区中央凸起地带;西宁地区地热储层埋深主要在700~1600 m,水温30~70 ℃,主要为SO4·Cl—Na水化学类型,溶解性总固体1.85×103~4.80×104 mg/L;回灌过程中结垢以碳酸钙结垢为主,当回灌水与地下热水性质相近时,结垢风险主要发生在回灌井筒中,地层结垢风险较小,而当回灌水与地下热水性质差异较大时,不配伍性将导致地层结垢风险大大提高,其中药王泉与DR2005原1∶ 1混合时结垢量最大可达177.57 mg/L,而其他地热水结垢量较小。根据以上特征,提出以下综合解决方案:物理防垢+管材防腐、系统增压防垢+管材防腐和地面预处理+管材防腐,并辅之以阴极保护防腐、优化排量、酸洗井筒等措施,可为今后保障地热水回灌能力措施的制定提供理论依据与技术支持。

       

      Abstract: The Xining Basin in Qinghai Province is rich in geothermal resources of low to medium temperature, but the geothermal reservoir is dominated by weakly consolidated sandstone containing clay minerals, and the geothermal water has high salinity, which causes a significant risk of scaling during reinjection. In this paper, based on the analysis of the geothermal genesis and resource distribution characteristics in the Xining Basin, different methods, such as the mineral solubility method and saturation index method, are used to assess the scaling tendency and risk in typical geothermal water during reinjection. The results show that the “convex in concave” structure of the Xining Basin is beneficial for the enrichment and warming of thermal groundwater in the deep geothermal reservoir, and at the same time, a large number of dissolved minerals are brought to the central bulge in the Xining Basin. The geothermal reservoir in the Xining Bain is mainly buried at a depth of 700−1600 m with water temperature of 30−70 ℃. The hydrochemical type is mainly of SO4·Cl—Na type, and the salinity range from 1.85×103 to 4.80×104 mg/L. The main scaling product during reinjection is CaCO3. When the characteristics of reinjection water and geothermal water are similar, the risk of scaling mainly occurs in the reinjection wellbore, and the risk of formation scaling is relatively small. When the characteristics of reinjection water and geothermal water are quite different, the incompatibility will greatly increase the risk of formation scaling. Among them, when the water from Yaowangquan is mixed with that from DR2005Y by 1∶1, the maximum scaling amount can reach 177.57 mg/L, while the scaling amount from other geothermal water is smaller. Based on the above characteristics, three sets of comprehensive measures are proposed as the follows: physical anti-scaling + pipe anti-corrosion, system pressurization anti-scaling + pipe anti-corrosion and ground pretreatment + pipe anti-corrosion, supplemented by measures such as cathodic protection anticorrosion, optimized displacement, and pickling the wellbore. The results of this study can provide theoretical basis and technical support for the formulation of measures to ensure the reinjection capacity of geothermal water in the future.

       

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