Fluid flow in the Earth: the influence of dehydration reactions and stress

岩石可能含有孔（孔隙），就像湿海绵中的孔一样，可能充满水或其他流体。这些孔隙中的流体压力可能与岩石所支撑的固体压力不同。流体压力的变化可能会引起地震，因此了解是什么控制着它是很重要的。我们将讨论三种与流体压力相关的影响。1.许多矿物在固体结构中含有H2O，在加热过程中或在其他情况下（包括周围压力下降），这被称为脱水反应。然后，释放的流体可以改变流体压力。流体压力影响反应速率，并受反应速率的影响-这是反馈。但是固体压力也会影响反应进程吗？这一点是人们对反应行为了解最少的一个方面，但它与地球上的一个相当普遍的情况有关。2.如果岩石被压实或以其他方式变形（如挤压海绵），流体压力就会改变。岩石比海绵坚固得多，所以我们需要了解它改变形状的速度（改变孔隙的体积，从而改变孔隙内的压力）。3.流体可以通过连通的孔隙流动，从而消散异常压力。我们需要测量和了解渗透性，也就是流动的容易程度。一般来说，反应伴随着变形和流体流动。我们的研究将通过对天然材料的实验和理论建模，揭示这三个过程的相关影响。我们将在实验中使用矿物石膏（在相当低的温度下进行脱水反应）和蛇纹石：作为完整的块（实际岩石，流体流动困难），以及作为高度多孔的粉末（高渗透性，流体流动容易）。一组实验将在反应温度以下进行，因此我们可以在没有其他影响的情况下检查变形行为。其他组将高于反应温度，以检查固体压力、流体压力和时间对反应进程的影响，以及随后对流体压力的反馈。数学建模需要将结果外推到大的岩石体（太大而不能直接进行实验）和地质时间尺度（几年到几百万年）;我们将与实验并行进行。我们的结果将有助于理解流体和岩石压力不同的各种情况：这里有两个例子。地震可能是由流体压力变化引发的，但地震本身也会改变流体压力。这又可能导致脱水反应（或相反的再水化反应），其再次改变压力场。在地热能领域，流体通过多孔岩石移动，但通常具有化学反应性。我们将应用我们的研究结果来了解地热田的变质变化是如何发生的，以及这些变化如何改变孔隙度和流体流动。我们的目标是NERC主题“地球系统科学3.3b：地球内部动力学及其在地表的表现”的核心，我们引用其中的内容：“许多自然灾害过程取决于材料特性和动力学过程，这些过程的特征或理解很差。这些问题最好通过对天然或类似材料进行实验室测量和实验来解决。主要的挑战出现了，因为许多危险的过程涉及复杂的多相混合物（气体，固体，液体），其性质要么是表征或理解不足。变形介质中的反应流体流动就是这样一个动态过程。

Rocks may contain holes (pores) which, like those in a wet sponge, may be filled with water or other fluids. The fluid pressure in these pores may not be the same as the solid pressure the rock is supporting. Changes in fluid pressure may cause earthquakes, so it is important to understand what controls it. There are three linked influences on fluid pressure which we will address. 1. Many minerals contain H2O within the solid structure and this is given off as fluid during heating, or under other circumstances including a drop in surrounding pressure: this is called dehydration reaction. The fluid given off may then change the fluid pressure. The fluid pressure influences and is influenced by the reaction rate - this is feedback. But does the solid pressure influence reaction progress as well? This point is the least understood aspect of reaction behaviour, yet relates to a quite general situation in the Earth. 2. Fluid pressure is changed if the rock is compacted or otherwise deformed (like squeezing the sponge). Rock is much stronger than sponge, so we need to understand just how fast it will change shape (changing the volumes of pores and hence the pressure within them). 3. Fluid can flow through connected pores, thus dissipating anomalous pressures. We need to measure and understand the permeability, that is, the ease of flow. In general the reaction is accompanied by deformation and by fluid flow. Our research will unravel the linked effects of these three processes, using experiments on natural materials as well as theoretical modelling. We will use the minerals gypsum (which undergoes dehydration reactions at quite low temperatures) and serpentine in experiments: as intact masses (actual rock, with fluid flow difficult), and as highly porous powders (high permeability, fluid flow easy). One group of experiments will be run below the reaction temperature, so we can examine the deformation behaviour in the absence of other effects. Other groups will be above the reaction temperature so as to examine the effects of solid pressure, fluid pressure and time on reaction progress, and the consequent feedbacks on fluid pressure. Mathematical modelling is required to extrapolate results to large bodies of rock (too large to run experiments on directly) and geological timescales (years to millions of years); we will conduct this in parallel with experiments.Our results will inform understanding a great variety of situations in which fluid and rock pressures are different: here are two examples. Earthquakes may be triggered by fluid pressure changes but will themselves change fluid pressure. This in turn may lead to dehydration reactions (or the reverse, rehydration reactions) which again modify the pressure field. In geothermal energy fields, fluids move through porous rock but are often chemically reactive. We will apply our results to understanding how metamorphic changes in geothermal fields occur, and how these modify porosity and fluid flow. Our objectives are core to NERC Theme "Earth System Science 3.3b: Dynamics of the Earth's Interior and their Manifestation at the Surface", from which we quote:"Many natural hazards processes depend on material properties and dynamic processes that are poorly characterised or understood. These can be best addressed through laboratory measurements and experiments on natural or analogue materials. Major challenges arise because many hazardous processes involve complex multiphase mixtures (gas, solid, liquid) whose properties are either poorly characterised or understood".Reactive fluid flow in deforming media is one such dynamic process.