Localized buoyant convection in porous media: plumes and dispersion

由浮力驱动的流动的例子在自然界、工业和日常生活中比比皆是，从大气对流到炉灶上热水壶升起的蒸汽。不太明显，但同样重要的是，在多孔介质中，热/冷流体通过固体颗粒之间的间隙导航的浮力驱动的流动。事实上，多孔介质中的浮力对流与能源系统有关，例如热能储存，提高石油采收率的方法，如蒸汽辅助重力排水或循环蒸汽增产，以及二氧化碳（CO2）或酸性气体（CO2和硫化氢的混合物）的地质封存，这些都是由电力和石油生产产生的。******这里提出的研究，虽然重点是基本的，但最主要的动机是后一个例子。为此，必须确定注入地层的二氧化碳或酸性气体永久隔离的精确条件。尽管有多种机制可以使注入物固定（毛细管捕获等），但二氧化碳和酸性气体比含水层盐水更具浮力，因此倾向于从一个地质层上升到另一个地质层。固定和垂直迁移之间的竞争，远非纯粹的学术兴趣，决定了地质封存项目所需的大量公共和私人资本支出实际上是否合理。******在我的研究中，我将使用理论和实验室实验来推进我们目前对多孔介质中浮力对流的理解。将进行三个相互关联的项目。首先，我将考虑有浮力的羽流对倾斜界面的冲击，在倾斜界面中，流体分别在流过上下两层时容易和困难。这模拟了一种情况，即浮力二氧化碳或酸性气体羽流撞击渗透率相对较小的盖层（可能破裂）。根据这个基础流，并与真实的地球物理情景相一致，然后我将允许一部分注入物溶解到周围的储层流体中。虽然溶解剂的体积很小，但预计对流动动力学的影响很大。最后，再次与实际流动相一致，我将具体解释含水层盐水中二氧化碳或酸气的有限混相性。这样做需要考虑表面张力和其他影响。******模型预测和测量数据可以适应盆地尺度的地质算法，缺乏足够的分辨率来充分描述精细空间尺度上的流动细节。相反，需要对注入排水、平流和溶解之间的权衡进行参数化。为此，研究的一个更广泛的目标是以对其他研究人员、行业从业者、监管机构和政策制定者有意义的方式收集、解释和综合数据。**

Examples of buoyancy-driven flow abound in nature, industry and everyday life from atmospheric convection to the steam that rises from a hot kettle on the stovetop. Less obvious, but equally important, is buoyancy-driven flow within a porous medium whereby hot/cold fluid navigates through the interstitial spaces between solid grains. Indeed, buoyant convection within porous media is relevant to energy systems e.g. thermal energy storage, methods of enhanced oil recovery such as steam-assisted gravity drainage or cyclic steam stimulation, and the geological sequestration of either carbon dioxide (CO2) or acid-gas (a mixture of CO2 and hydrogen sulfide), which result from the production of electricity and oil.******The research proposed here, though fundamental in focus, is motivated most especially by this latter example. To this end, one must define the precise conditions under which the CO2 or acid-gas injected into formation will remain permanently sequestered. Although there are a variety of mechanisms that allow the injectate to become immobilized (capillary trapping, etc.), CO2 and acid-gas are more buoyant than, say, aquifer brine and tend therefore to rise from one geological layer to the next. The competition between immobilization and vertical migration, far from being of purely academic interest, determines whether the large outlays of public and private capital necessary for geological sequestration projects are, in fact, justified.******In my research, I will use theory and laboratory experiment to advance our current understanding of buoyant convection in porous media. Three interconnected projects will be pursued. Firstly, I will consider the impingement of a buoyant plume on a sloping interface where the fluid has an easy and difficult time, respectively, flowing through the layers below and above. This mimics a scenario in which a plume of buoyant CO2 or acid-gas strikes a (possibly fractured) cap rock layer having a comparatively small permeability. To this base flow, and consistent with real geophysical scenarios, I will then allow some fraction of the injectate to dissolve into the ambient reservoir fluid. Although the volume of dissolving injectate is small, the impact on the flow dynamics is expected to be large. Finally, and again consistent with real flows, I will then specifically account for the limited miscibility of CO2 or acid-gas in aquifer brine. Doing so requires accounting for surface tension among other effects.******Model predictions and measured data may be adapted into basin-scale geological algorithms that lack sufficient resolution to fully describe flow details at fine spatial scales. Instead, parameterizations of the tradeoffs between injectate drainage, advection and dissolution are required. To this end, a broader objective of the research is to collect, interpret and synthesize data in a way that is meaningful to other researchers, industry practitioners, regulators and policy makers. **