深部流体运动-热传-地球化学过程的浅层响应机理和定量化研究

Deep fluids with high temperature and pressure move up along fault zones. With the pressure and temperature decreasing, the supercritical fluids gradually transform into subcritical fluids (or gases). The most common and abundant constituents of deep fluids are CO2 and H2O. Deep fluids interact with surrounding rocks, and then change the chemical composition. The upward fluids coming from channels often carry a lot of information about the deep geological activities. This proposal will use field survey, laboratory experiment, numerical simulation and natural analogue methods, to investigate the coupled mechanisms of deep fluids flow-heat transfer-geochemistry-rock mechanics, to establish a numerical modeling system of this coupled multiple fields, to predict the responses at the shollow and land surface of fluid pressure, temperature, chemical and isotope composition in typical study sites, and to evaluate the escape rates of geothermal and CO2 under different control conditions. The proposed research involving a number of disciplinaries including underground seepage, geochemistry, petrology and geothermics, will promote the multi-disciplinary study for underground complex environments, and accelerate national and international researches in this field. The investigation will have not only great significance for fundamental geosciences, but also have broad practical application prospects. The numerical system developed by this proposed project will provide scientific methods to solve the problems related to geothermal, and CO2 geological storage.

高温高压的深部流体会沿着断裂带向上移动。随着压力和温度的降低，超临界流体逐渐变成次临界流体（或气体）。深部流体最丰富、最常见组分是H2O和CO2。深部流体运移过程中与围岩发生地球化学反应，改变流体化学组分。通道逸出流体会携带丰富的深部地质活动信息。本项目采取野外调查、室内实验、数值模拟和天然类比相结合的方法，研究深部流体运动-热传导-地球化学-岩石力学耦合过程和地表响应反馈机理和定量化规律，建立多场耦合数值模拟系统，评价典型区域流体压力、温度、水化学和同位素成分等地表响应的深部流体活动和运移过程，以及不同条件下地热水、CO2逃逸速率。该研究涉及渗流力学、地质、水文地质、地球化学、地热和岩石力学等多学科，将推动地下复杂环境的多学科交叉研究和国内国际上该领域的发展。不仅对基础地学研究有重大意义，且具有较宽广的地质工程应用前景，为有关地热能开发和CO2储存安全等问题的解决提供科学理论和技术方法。

以我国青海共和—贵德盆地地热异常成因为研究对象，利用浅层和地表监测的流体压力、温度、水化学和矿物成分、同位素数据，采用室内实验和数值模拟相结合的手段评估了断裂控制下深部流体流动、化学元素运移、热传导以及岩石力学过程；分析了深部热流体沿构造断裂泄漏至浅部地层，对通道渗透性的改变作用；进而根据流体温度-压力-化学和同位素成分的浅层和地表响应规律，确定了深部流体的温度、活动状态与作用过程。.通过该项目研究，在以下方面取得重要进展：(1) 补充了地球化学反应热力学数据库，使其适用条件拓宽至0<T<600℃, 0<P<1000 MPa且流体相密度大于350k g/m3；(2)开发了水-热-同位素耦合数值模拟程序，使得同位素数据可作为数值模型的约束条件，为根据浅部同位素响应推测深部流体活动过程提供了定量化的模型；(3) 构建了流体流动、热传导、化学反应及应力应变四场耦合模型，并实现并行化计算，为深部流体活动过程及浅部响应特征提供了分析和预测工具。