Modeling Flow in Porous Media with Vugular Meso-scale Heterogeneities

沉积岩有时含有被称为洞穴的空洞区域，这些空洞比通常的粒间孔隙大得多。洞穴非均质性提出了在现场尺度上理解流体流过这类岩石的实际和理论问题。例如，标准抽样方法的规模太小，无法解决这些异质性。此外，要确定正确的物理公式来模拟流动或解释流动测量并不是一件容易的事，而且还不清楚传统的均化方法是否适用。在这个项目中，研究人员将含有厘米级洞穴的白垩纪碳酸盐岩大样本(约17,000立方厘米)的微观(CT扫描)和宏观测量直接与高分辨率的流场计算联系在一起。该框架允许测试样品几何形状中流动的不同物理模型。具体目标是：(1)将样品的CT扫描像素映射到渗透率和孔隙度；(2)模拟微观系统中的流动；(3)确定单相流的宏观尺度控制关系；(4)根据微观尺度的表征确定宏观模型参数。对算法和升级程序的研究是为了实现第二和第三个目标。随后的数值实验通过改变洞穴的连通性和基质材料的渗透率分布来确定不同的沉积环境和成岩历史的影响。这最终导致了在全场模拟中更有信心地预测洞穴介质中的流动的能力。流体在多孔岩石中的流动具有经济和环境意义。例子包括石油和天然气生产，获得充足的供水(地下水约占美国用水量的三分之一，许多城市完全依赖水井)，以及修复超级基金场地和能源部许多设施的地下污染。这些水流流经的沉积岩有时包含相对较大的孔洞或空洞区域，称为洞穴。化石碎片的溶解是在碳酸盐岩中形成洞穴的一种常见机制，碳酸盐岩包含了世界一半以上的石油储量，并构成了美国许多最大的含水层。洞穴比岩石颗粒之间的小得多的孔隙空间更有利于流体流动，这就提出了理解大规模流动的实际和理论问题。该项目旨在为这种类型的岩石建立模型，以预测数百码到几英里范围内的有效流动特性。由于在这些距离上直接进行实验是不可行的，所以这项研究的一个重要组成部分是将中等规模的物理实验和大规模的计算实验相结合。这一努力还依赖于数值算法和建模技术的基础研究。建立控制这种岩石中流体流动的正确关系，可以从全场模拟中获得更有信心的预测。

Arbogast0074310 Sedimentary rocks sometimes contain void regions called vugs that are much larger than the usual intergranular pores. Vugular heterogeneities raise both practical and theoretical problems for understanding fluid flow through such rocks at the field scale. For example, standard sampling methods are at a scale too small to resolve these heterogeneities. Moreover it is nontrivial to identify the correct physical formalism for modeling flow or interpreting flow measurements, and it is not clear that traditional homogenization approaches are applicable. In this project, the investigators tie microscopic (CT scan) and macroscopic measurements of a large sample (about 17,000 cubic cm) of Cretaceous carbonate rock containing centimeter-scale vugs directly to high-resolution computation of flow fields. This framework allows the testing of different physical models for flow in the geometry of the sample. The specific objectives are to: (1) Map CT scan pixels of the sample to permeability and porosity; (2) Simulate flow in the micro-scale system; (3) Determine the macro-scale governing relations for single phase flow; and (4) Determine the macroscopic model parameters in terms of the microscale characterization. Research in algorithms and upscaling procedures is conducted to achieve the second and third objectives. Subsequent numerical experiments determine the influence of alternative depositional environments and diagenetic histories by changing the connectivity of the vugs and the permeability distribution of the matrix material. This results finally in the ability to more confidently predict flow in vugular media in full-field simulations. The flow of fluids through porous rock is of economic and environmental interest. Examples include oil and gas production, obtaining adequate water supplies (groundwater accounts for about one third of the water used in the US, with many cities depending exclusively on wells), and remediating subsurface contamination at Superfund sites and many Department of Energy facilities. The sedimentary rocks through which these flows occur sometimes contain relatively large holes or void regions called vugs. The dissolution of fossil fragments is a common mechanism for creating vugs in carbonate rocks, which contain more than half the world's oil reserves and comprise many of the biggest aquifers in the US. Vugs are more conducive to fluid flow than the much smaller pore space between the rock grains, and this raises both both practical and theoretical problems for understanding large-scale flows. This project aims to construct models for this type of rock that predict the effective flow properties over hundreds of yards to several miles. Because direct experimentation over these distances is not feasible, an essential component of the research is the integration of intermediate-scale physical and large-scale computational experiments. This effort also relies on basic research in numerical algorithms and modeling techniques. Establishing the correct relations governing the flow of fluids in such rocks enables more confident predictions from full-field simulations.