Graduation Year

2021

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Jeffrey A. Cunningham, Ph.D.

Committee Member

Andres Tejada-Martinez, Ph.D.

Committee Member

Amy L. Stuart, Ph.D.

Committee Member

Mahmood Nachabe, Ph.D.

Committee Member

David Murphy, Ph.D.

Committee Member

Brian Space, Ph.D.

Keywords

Color gradient model, Drainage, Imbibition, Lattice Boltzmann method, Pore structure, Pore-scale flow

Abstract

Many environmental issues deal with the movement of immiscible fluids in the subsurface, e.g., cleanup of oil spills and geological carbon dioxide sequestration. Engineers face a constant challenge to improve the efficiency of these processes. This can be facilitated by studying the underlying physics of how fluids flow and interact in these systems.

Traditionally, lab experiments can provide reliable information about fluid architecture in porous medium, such as trapped fluid volumes and contact area between two immiscible fluids (interfacial area). However, these methods can be expensive and tedious. A well designed numerical experiment is not only able to describe fluid behavior but can forecast this behavior over time and space scales not achievable in the lab. Numerical models can serve as excellent tools that enable visualization of direct fluid interactions in the porous domain.

The development of fluid interfaces, i.e., interfacial area, is a key component in multi-phase flow, that influences chemical mass transfer in the system. However, it is not clearly understood how interfacial area evolves as a function of time during multi-phase flow due to limitations in lab experiments.

Therefore, the objective of this research is to assess how pore-scale factors, such as grain morphology, can affect the temporal development of interfacial area during multi-phase flow. Three morphological characteristics were selected: grain-size distribution, grain circularity, and grain edges (roundness).

The research objective was achieved by the following approach: generating an ensemble of 2D porous media; developing and validating a multi-phase lattice Boltzmann model; conducting simulations of immiscible displacement of fluid in the ensembles of 2D porous domain. The influence of the grain morphology was analyzed by calculating the interfacial area and fluid saturation as a function of time during the simulation. In addition, the 2D numerical model was also extended to 3D for future research investigations, and preliminary drainage simulation was conducted in a 3D porous media.

The results from the simulations highlighted three distinct effects of grain morphology. The effect of grain-size distribution was more prominent at a coefficient of uniformity equal to 2.29. It was seen that the temporal evolution of interfacial area was same for all uniform to moderately sorted groups, except for the group with a coefficient of uniformity equal to 2.29. This group showed a delay in acquiring peak interfacial areas. The behavior of grain circularity did not prominently influence the temporal evolution of interfacial area but had more influence on the trapped wetting phase volumes. Overall circular grains showed higher trapped wetting phase volume. Moreover, grain edges did not show a significant impact on the formation of peak interfacial area values within the comparing groups. However, collectively the grain characteristics showed vastly different behavior. It is important to note that these results are only applicable to fluid pairs with unit density and viscosity ratios, under high flow conditions.

These outcomes are promising and important as they indicate that grain morphology can play a major role in multi-phase fluid trapping and transport. This provides detail about the fluid architecture present in the subsurface which can affect efficiency of a treatment process. Information about these systems contributes to improving the engineering of cleanup of oil spills and carbon dioxide sequestration.

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