PoreFlow: Visualizing multiphase flow in porous media with neutron imaging

About the project

Understanding multi-phase flow in porous materials is key to resolving a range of pressing societal challenges, including fresh water supply, living processes, and contamination in soil and rocks. During the last few years, tremendous progress in the physics of porous media has been made both theoretically and experimentally. X-ray computed tomography (CT) now allows 3D microscopic imaging of the interior of opaque porous materials, with resolution often better than 100 nm. Still, owing to the weak interactions between X-rays and light elements, it remains difficult to obtain information about liquids inside the pores, not to mention their dynamics.


In the PoreFlow project, as part of CoE PoreLab, we aim to exploit the inherently higher sensitivity to light elements offered by neutrons to quantitatively monitor liquid dynamics in porous materials in 3D and real time. A top international team with complementary know-how in the fields of physics, neutron imaging, geophysics and life sciences has been assembled, including five Norwegian professors from NTNU, UiO and USN. Starting out with idealized test systems based on microfluidics combined with inert bead packs, the project aims to ultimately image liquid transport in soil, porous rocks and tissue. An important ambition is to challenge existing theories on two-phase flow, including recently published works describing fluctuations in the steady state.


PoreFlow is of high relevance to the upcoming European Spallation Source (ESS), and an expressed aim of the project is to prepare Norwegian user communities within the physics, geo- and life sciences, including relevant industries, for the upcoming new possibilities offered by ESS.

In summary, the project aims to contribute to the understanding of multiphase flow in porous media through innovative use of neutron computed tomography - a topic with profound scientific and societal consequences.

Objectives

Primary objective: To further develop quantitative neutron microscopy as a tool for studying multiphase flow in porous media. This ability will be a substantial step towards solving several imminent societal challenges, in particular in the geo- and life sciences.

Secondary objectives: 

- Demonstrate quantitative 4D neutron imaging (time-resolved movies) of multiphase flow in both model (e.g. microfluidic) and natural (e.g. sandstone) samples.
- Demonstrate enhanced imaging performance by combining (low resolution, high contrast) neutron tomography with (high resolution, low contrast) X-ray tomography through computational imaging methods.
- Experimentally challenge existing theories on multi-phase flow in porous media.
- Prepare and educate relevant Norwegian industry and academic groups for the opportunities offered by the upcoming European Spallation Source (ESS).

Outcomes

PoreFlow is deeply motivated by pressing societal needs sorting under the geo- and life sciences and connects directly to UN development goals (#6 and #13) relating to the physical environment. The scientific goal of the project is an improved understanding of multi-phase flow in porous media through new experimental tools (viz. time-resolved neutron CT), which we believe will have immediate societal impact.


For the project partners, PoreFlow will markedly increase their know-how of neutron science in general, and imaging in particular. The sample systems will give important competence building with time-resolved studies, microfluidics and computational imaging, which are topics of high
importance for the future. The cross-disciplinary nature of the project will broaden the perspectives of all the partners.


Finally, an important consequence of PoreFlow is that the Norwegian preparedness for the upcoming ESS will be markedly improved, with trained scientists at several universities.

Background

Main hypothesis: Multi-phase flow dynamics in porous media and microfluidic devices can be quantitatively imaged by advanced neutron microscopy and tomography.


Secondary:
- Neutron CT allows monitoring liquid transportation of contaminants in natural porous samples of high societal importance, i.e. soil and porous rocks.
- Neutron CT allows monitoring liquid flow in biological tissue, notably bone and cartilage.


Methodology. We base PoreFlow on exploiting the unique possibilities that neutron imaging gives for contrast variation through systematic deuteration of the hydrogen-containing liquids. We foresee that by using high-resolution 3D structural data of the surrounding matrix from complementary X-ray CT (~5 µm) as a priori information, the lower-resolution neutron-CT data (~30 µm) with enhanced liquid contrast can be systematically image-enhanced to give higher resolution in both space and time. We thus aim for a sub-minute temporal resolution (in 3D) combined with micrometre spatial resolution. We note that developments in this direction have been implemented at the ICON beamline at PSI and at the D50 beamline at ILL, both sporting crossed beam setups combining X-ray CT with neutron CT. We are thus planning to carry out a substantial part of the project at these beamlines (see LoIs).


The last few years have witnessed a revolution in computational imaging, with software replacing optical hardware for high-performance microscopy. Some of the computational methods recently developed, notably CT reconstructions exploiting a priori knowledge, and compressed sensing, must also be applicable to maximize the overall neutron imaging performance. The temporal resolution of the experiments is inversely proportional to the number of projections, so obtaining statistically reliable 3D reconstructions from a minimal number of projections is of key importance. By quantifying the permeation of liquids in porous media models, we expect to be able to challenge the existing theories of two-phase flow, including recent steady state models  in unprecedented details with respect to parameters including Reynold numbers, miscibility, viscosity, fingering, capillarity, wetting coefficients, matrix porosity and tortuosity.


To facilitate the experiments while maintaining relevance to soils at the Earth surface, we shall limit the fluid pressure to being near ambient (say, 0 – 3 bars). For similar reasons, for the model systems of microfluidics combined with bead packs, we seek to avoid unnecessary complications with surface chemistry by choosing matrix materials inert to the permeating liquids. With natural samples, a complicating factor will be that reactive fluids may change the solid rock surfaces, leading to coupling between flow rate, transport of dissolved species, and stress in the solid. A significant part of the project will be carried out at USN, which is Norway’s leading academic environment for microsystems engineering. Specifically, we aim to design and construct a microfluidic cell that is transparent to both neutrons and X-rays in a crossed-beam geometry, with controlled temperature and supply of liquids for porous media model studies. In addition to carrying out and analyzing the performance of neutron CT as applied to dynamics of liquids in porous rocks and soil, we plan to exploit the unique imaging properties of neutrons with respect to hydrogen for studying bio-liquid distributions (i.e., blood) in bone and cartilage samples.

Financing

The Research Council of Norway.

Cooperation

The project is headed by Professor Breiby at NTNU, and the Njord Centre at UiO is a partner. The project team is comprised of young and established researchers from:

  • Norwegian University of Science and Technology (NTNU)
  • University of Oslo (UiO)
  • University of South Eastern Norway (USN),

The team members have a long history of cooperation within materials physics and microscopy, in terms of supervising master and PhD students, joint publications, sharing lab facilities, holding informal meetings to exchange knowledge and research ideas, and applying for joint projects. The multidisciplinary and highly competent project group should be able to provide significant cross-fertilization between the main branches of the project.

The scientific advisory group consists of Prof. Gibaud, Dr. Helgesen, Dr. Kästner, and Dr. Tengattini, who will participate in annual progress meetings and also be subcontractors and co-supervisors when adequate.

Publications

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Published June 1, 2021 4:32 PM - Last modified June 1, 2021 4:32 PM