Streaming potential in porous media: 2. Theory and application to geothermal systems
Streaming potential in porous media: 2. Theory and application to geothermal systems
复制标题
DOI：
10.1029/1999jb900090
复制
发表时间：
1999-09
影响因子：
--
通讯作者：
A. Revil;H. Schwaeger;L. Cathles;P. Manhardt
中科院分区：
文献类型：
--
作者：
A. Revil;H. Schwaeger;L. Cathles;P. Manhardt
与热液领域、火山活动和地下水流有关的自然电势和磁力异常越来越多地被观察到。到目前为止，还没有一个正式的理论基础来预测多孔材料的流动潜力。我们在这里建立了一个模型，给出了宏观本构方程和进入这些方程的材料特性。材料性质，如流动电势耦合系数，取决于孔隙流体矿化度、温度、水和气饱和度、平均颗粒直径和孔隙度。该模型的某些方面直接用实验室数据进行了成功的测试。流动电位随温度、粒度和含气饱和度的增大而增大，随矿化度的增大而减小。在地质构造尺度上，该模型解释了地热系统和火山中存在千米尺度的偶极自然电位异常。自然电位正异常与流体排出区有关，而自然电位负异常与流体补给区有关。在活动热液场表面确定的自然电位异常图似乎是绘制流体补给区和排泄区的一种强有力的方法。在自由对流的情况下，对流图案的涡旋产生磁场。涡度越大，相关的磁场就越大。由此可见，热液系统由于在这些系统的地下流动的孔隙流体，起到了天然的地缘生物的作用。
Self-potential electric and magnetic anomalies are increasingly being observed associated with hydrothermal fields, volcanic activity, and subsurface water flow. Until now a formal theoretical basis for predicting streaming potential of porous materials has not been available. We develop here a model giving both the macroscopic constitutive equations and the material properties entering these equations. The material properties, like the streaming potential coupling coefficient, depend on pore fluid salinity, temperature, water and gas saturations, mean grain diameter, and porosity. Some aspects of the model are directly tested with success against laboratory data. The streaming potential increases with temperature, grain size, and gas saturation, and decreases with salinity. At the scale of geological structures the model provides an explanation for the presence of kilometer-scale dipolar self-potential anomalies in geothermal systems and volcanoes. Positive self-potential anomalies are associated with fluid discharge areas, whereas negative self-potential anomalies are associated with fluid recharge areas. Self-potential anomaly maps determined at the surface of active hydrothermal fields appear to be a powerful way of mapping the fluid recharge and discharge areas. In the case of free convection the vorticities of the convection pattern generate a magnetic field. The greater these vorticities, the greater the associated magnetic field. It follows that hydrothermal systems act as natural geobatteries because of the flow of pore fluids in the subsurface of these systems.