Chemical Transport in Partially Saturated Porous Media

化学品在多相流中的输送在许多工程问题中得到应用，其中许多问题发生在自然环境中，包括CO2的地质储存或提高石油采收率。在后一种情况下，油和水共存于孔隙空间中，并且它们的空间分布受两种流体之间的平均驱替速度和粘度差异控制。在通过注水进行生产期间，毛细管作用导致形成不连续的油相，该油相保持被捕获到孔隙空间中，作为储层中的所谓残余相。表面活性剂-聚合物（SP）驱油可以通过降低油水界面张力和流度比来提高采收率。然而，由于表面活性剂成本和工艺复杂性，现场应用受到限制。残余相通过增加流动路径的弯曲度和控制盐水相中的速度场而充当高效分散剂，从而影响盐水-表面活性剂制剂与油接触的能力。这种情况进一步复杂化的表现形式的其他过程：（i）保留的表面活性剂，作为吸附到固体表面上的结果;（ii）乳化的油相，其形成下的流动可能大大不同于平衡的情况。了解两相之间的混合过程在改进化学EOR技术的设计中是至关重要的，但是目前控制混合和随后的油的流动的关键机制还没有完全理解，本项目的目的是量化和描述饱和度（含水量）对溶质分散和混合的影响，以及其对油采收率的影响。我们将部署实验室岩心驱替实验增强原位成像，以提供直接观察的溶质扩散在部分饱和的岩石，包括各种SP配方和不含聚合物的动态。所提出的方法的一个独特的方面是结合使用X射线计算机断层扫描（XCT）和正电子发射断层扫描（PET），使收购的一套基准实验显示岩石/矿物的异质性，流体分布和化学运输在砂岩和碳酸盐岩。一维和三维数值模型将用于支持实验室观测，并获得描述部分饱和多孔介质中混合过程的有用参数。

The transport of chemicals in multiphase flows finds applications in many engineering problems, many of which occur in natural environments, including the geological storage of CO2 or enhanced oil recovery. In the latter case, oil and water coexist in the pore space, and their spatial distribution is controlled by the average displacement velocity and the viscosity contrasts between the two fluids. During production by waterflooding, capillary action leads to the formation of a disconnected oil phase that remains trapped into the pore space, as a so- called residual phase in the reservoir. Surfactant-polymer (SP) flooding can increase oil recovery by lowering both the water-oil interfacial tension and mobility ratio. However, field application is limited due to surfactant costs and process complexity. The residual phase acts as a highly effective disperser by increasing the tortuosity of the flow paths and controlling the velocity field in the brine phase, thereby affecting the ability of the brine-surfactant formulation to get in contact with the oil. This situation is further complicated by the manifestation of other processes: (i) retention of the surfactant, as a result of adsorption onto solid surfaces; (ii) emulsification of the oil phase, the formation of which under flow may greatly differ from an equilibrium situation. Understanding the mixing process between both phases is critical in the design of improved chemical EOR techniques, but at present the key mechanisms that control mixing and the subsequent mobilization of the oil are not fully understood.The aim of this project is to quantify and describe the impact of saturation (water content) on solute dispersion and mixing, and its effect on oil recovery. We will deploy laboratory core-flooding experiments augmented by in-situ imagery to provide direct observations of the dynamics of solute dispersal in partially saturated rocks, including various SP formulations with and without polymer. A unique aspect of the proposed approach is the combined use of X-ray Computed Tomography (XCT) and Positron Emission Tomography (PET) to enable the acquisition of a suite of benchmark experiments showing rock/mineral heterogeneity, fluid distribution and chemical transport in both sandstone and carbonate rocks. One- and three- dimensional numerical models will be used to support laboratory observations and to obtain useful parameters that describe the mixing process in partially saturated porous media.