Ingrid Tomac

Experimental Investigation of Particle Agglomeration Effects on Slurry Settling in Viscous Fluid

This paper presents fundamental analysis and micromechanical understanding of dense slurry behavior during settling in narrow smooth and rough slots. Particularly, this study seeks to contribute toward better understanding of dynamics of particle–particle and particle–wall interactions in viscous fluids using simple experiments. The findings of this study are applicable in a wide variety of problems, for example sediment transport, flow and transport of slurry in pipes, and industrial applications. However, the results interpretation focuses on better understanding of proppant flow and transport in narrow fractures. A sequence of experiments image frames captured by video camera is analyzed with particle image velocimetry (GeoPIV). The measurements include vertical velocities and displacement vectors of singular and agglomerated particles and larger area of formed slurry. Results present novel insights into the formation and effects of agglomerates on general slurry settling, and are supplemented with a comparison with previously published theoretical and empirical relationships. This work also emphasizes a role of particle–particle interactions in promoting agglomeration in viscous fluid. Particularly, a thin layer of viscous fluid between approaching particles dissipates particle kinetic energy due to lubrication effect. Lubrication effect is more pronounced when particles are constrained between two narrow walls and interact frequently with each other. Fluid tends to flow around agglomerated particles, and agglomerates remain stable for prolonged time periods gravitationally moving downward. The relative amount and size of agglomerated affects general settling of the slurry. It was found that fluid viscosity due to lubrication effect promotes agglomeration, and therefore, the overall slurry settling relatively increases at higher fluid viscosities. The results of the presented work have impact on various industrial and engineering processes, such as proppant flow and transport in hydraulic fractures, sand production in oil reservoirs, piping failure of dams and scour of foundation bridges.

Effect of Fracture Surface Damage on Fluid Flow and Transport in Geo-reservoirs

This study quantifies the effect of fracture surface damage caused by secondary processes during CO2 injection on fluid and gas flow and transport in sandstone geo-reservoirs. Numerical approach uses Discrete Element Method (DEM) and the Lower-dimensional Discrete Fracture Model (LDFM) for better understanding spatially-localized and time-varying rock permeability and porosity changes induced by pressurized fluid and gas flow. Tensile and shear micro-cracks may develop in rock mass adjacent to existing fractures with flowing fluid due to the stress re-orientation or localized pressure peaks. As a result, micro-crack damage changes porosity and permeability of the near-fracture zone allows enhanced flow properties, which affects the reservoir large-scale fluid flow dynamics. DEM models micro-scale stress induced damage on a smaller rock element locally subjected to the confining stresses and fluid pressure. DEM uses implicit finite differences for solving stress-strain field in low permeability rock, which is discretized with a system of bonded spherical particles. The fluid flow field uses fluid channels and reservoirs between particles and is fully coupled with the DEM. During the time-stepping procedure, fluid pressure induces stresses on adjacent particles, which displace and open the fluid channels causing the initial permeability increase. In addition, when the fluid pressures exceed tensile or shear bond strength between particles, new micro-cracks occur. Subsequently, the LDFM uses an input function obtained from the DEM model, which relates local porosity and permeability to the fluid pressure in fracture. The LDFM simulates the reservoir-scale gas-water flow through fractured porous media. The two phase flow field is represented with a set of differential equations, which are solved using a fully coupled, fully implicit vertex-centered finite volume method that is known for its robustness and wide range of applicability. Furthermore, the study employs the novel DEM-LDFM coupled approach for investigating the effects of fracturing fluid pressure, gas injection pressure, dynamic viscosity, and fluid and gas compressibility on the evolution of rock damage and rock properties from their initial values due to micro-cracks. Finally, the temporal and spatial change of fracture porosity and permeability as a function of local pressure allows an enhancement of the LDFM fracture parameters and an insight into effects on the large-scale reservoir model.