Dynamic, in-situ imaging of capillary imbibition in rock using simultaneous neutron and X-ray computed tomography

最常见的二次采油方法是注水，即将水注入油层，将油层中的石油驱替到生产井中。在理想情况下，注入的水(注水)会将石油均匀地“扫射”到油井。然而，在包含世界石油储量约一半的裂缝性油藏中，洪水优先流经裂隙网络，在岩石基质中留下很大一部分原始石油。然后，更缓慢地，裂缝中的洪水通过浮力、扩散和自发(毛细管驱动)渗吸进入岩石基质，驱替遗留下来的石油。在均匀润水(亲水)条件下，渗吸的显著特征被很好地确立。然而，在油藏特有的混湿条件下，颗粒表面在孔隙尺度和亚孔隙尺度上表现出润湿性的非均质性，对于油藏的渗吸仍有许多基本问题没有得到解答。为了设计有效的裂缝性油藏采油方案，必须定量地确定岩石润湿性和渗吸行为(即速率和最终采油)之间的关系。项目团队的两名成员需要资金前往位于美国盖瑟斯堡的国家标准与技术研究所(NIST)中子研究中心，进行一系列四次旅行，在他们的X射线/中子成像设施进行实验。我们将通过吸收含有不同润湿性改变成分的油的水来动态成像石灰岩样品中的油的置换。观察到的渗吸行为的差异将与方解石衬底上石油/盐水界面的接触角相关联；这个宏观接触角将成为我们对岩石润湿性的测量。这项工作将由一个由阿伯丁大学具有实验流体力学、岩石力学和医学成像专业知识的学术研究人员组成的多学科团队与NIST中子物理组的物理学家共同完成。据我们所知，NIST是唯一同时具有X射线和中子成像能力的高通量用户设施。此外，NIST将为我们提供四个高度专业化的恒压模式注射泵，我们需要它们来建立统一的初始油饱和度。该项目的两个关键目标是巩固申请者和NIST指定物理学家之间的合作，并评估NIST新的组合X射线/中子成像能力的可实现规格。因此，该项目将为项目组未来的工作提供基础，该工作将导致在可能的润湿性和初始流体分布的全部范围内建立毛细管驱动的多孔介质中两相流动的预测模型。应用领域包括石油工程(从裂缝性储油层开采石油)、地质二氧化碳储存(关井期间地层卤水向注水井的迁移)、岩土工程(废物库的地下渗漏)、建筑(水渗入混凝土)、洪水管理、土壤修复和灌溉(土壤中的水渗透)。

The most common method of secondary oil recovery is waterflooding, whereby water is injected into a reservoir to displace the oil in the reservoir towards production wells. Under ideal conditions, the injected water (flood water) uniformly 'sweeps' the oil towards the wells. However, in fractured reservoirs, which contain around half of the world's oil reserves, the flood water preferentially flows through the network of fractures, leaving behind a large fraction of the original oil in the rock matrix. Then, more gradually, flood water in the fractures enters the rock matrix by buoyancy, diffusion, and spontaneous (capillary-driven) imbibition, displacing the oil that was left behind.Salient features of imbibition under uniformly water-wetting (hydrophilic) conditions are well established. However, many fundamental questions remain unanswered for imbibition under mixed-wet conditions characteristic of oil reservoirs, under which grain surfaces display heterogeneity in wettability at the pore scale and sub-pore scale. To design efficient oil recovery schemes for fractured reservoirs, the relationship between rock wettability and the imbibition behaviour (i.e., rate and ultimate oil recovery) must be determined quantitatively.Funds are requested for two members of the project team to travel to the National Institute of Standards and Technology (NIST) Center for Neutron Research in Gaithersburg, USA in a series of four trips to perform experiments at their X-ray/neutron imaging facility. We will dynamically image the displacement of oil within limestone samples by imbibing water for oils containing different wettability-altering constituents. Observed differences in imbibition behaviour will be correlated to the contact angle of the oil/brine interface on a calcite substrate measured independently; this macroscopic contact angle will be our measure of rock wettability.The work will be undertaken by a multidisciplinary team comprising academic researchers with a combined expertise in experimental fluid mechanics, rock mechanics, and medical imaging at University of Aberdeen, together with physicists in the Neutron Physics Group at NIST. To our knowledge, NIST is the only high flux user facility with simultaneous X-ray and neutron imaging capabilities. Moreover, NIST will provide us with four highly specialized, constant pressure mode syringe pumps which we need for establishing uniform initial oil saturation.Two key aims of the project are to consolidate the collaboration between the applicants and the named physicists at NIST and to evaluate the achievable specifications of the new combined X-ray/neutron imaging capability at NIST for our samples. This project will thus provide the basis for future work by the project team which will lead to a physically meaningful, predictive model for capillary-driven, two-phase flow in porous media under the full range of possible wettability and initial fluid distribution. Applications include petroleum engineering (oil recovery from fractured reservoirs), geological CO2 storage (migration of formation brine towards the injection well during well shut-in), geotechnical engineering (subsurface leakage from waste repositories), construction (water infiltration into concrete), and flood management, soil remediation, and irrigation (water infiltration in soil).