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Pore scale interaction between matrix and fracture during miscible and immiscible CO2 injection was studied experimentally using visual models. Initially, visualization experiments were conducted on 2-D glass bead packed models by injecting n-heptane (solvent) displacing different kinds of processed oil. The focus was on the displacement patterns and solvent breakthrough controlled by matrix-fracture interaction and the pore scale behaviour of solvent-oil interaction for different fracture and injection conditions (rate, vertical vs. horizontal injection) as well as oil viscosity. Besides the visual investigation, effluent was also analyzed to calculate the solvent cut and oil recovery. Next, the process was modeled numerically using a commercial compositional simulator and the saturation distribution in the matrix was matched to the experimental data. The key parameters in the matching process were the effective diffusion coefficients and the longitudinal and transverse dispersivities. The diffusion coefficients were specified for each fluid and dispersivities were assigned into grid blocks separately for the fracture and the matrix. Finally, glass etched microfluidic models were used to investigate pore scale interaction between the matrix and the fracture. The models were prepared by etching homogeneous and heterogeneous micro scale pore patterns on glass sheets bonded together and then saturated with colored n-decane as the oleic phase. CO2 was injected at miscible and immiscible conditions. The focus was on visual pore scale analysis of miscibility, breakthrough of CO2 and oil/CO2 transfer between the matrix and the fracture under different miscibility, injection rate and wettability conditions. / Petroleum Engineering

Different scenarios for assembling rod-like and spherical colloidal particles using binary mixtures of partially miscible liquids were investigated experimentally. Suitable rod-like colloids were developed first. The subsequent studies of colloids in binary liquids consisted, on one hand, of systems where particles were partially wetted by both phases and, on the other hand, of systems where particles were completely wetted by the minority phase. A simple method to prepare large quantities of micrometer-sized akagan eite-silica core-shell rods was developed. These were proven to be very versatile, with the possibility of modifying their properties on different levels. The aspect ratio is simply controlled by a gradual growth of the silica shells. From them, hollow silica rods and rods with an increased responsiveness to a magnetic field could be obtained in straightforward ways. Bijels were prepared by trapping rod-like particles on a percolating liquid-liquid interface. The familiar bicontinuous organization of liquid domains was observed after structural arrest. At a fixed volume per particle it is demonstrated that for rod-like particles the domain size decreases faster with increasing quantity of particles than in the case of spherical particles. Additionally, the packing of the rods at the interface was elucidated, revealing several characteristic features. In particle-stabilized droplet emulsions rapid evaporation of the continuous phase and eventual full mixing of the liquid phases can leave a cellular network of particles. The formation and eventual stability of these networks were investigated in detail with confocal microscopy. When colloids are completely wetted by the minority component of an asymmetric binary mixture there can be substantial temperature and composition regimes outside the binodal where shear-induced aggregation can take place. This happens as adsorbed layers present at the particle surfaces coalesce and bind particles through a liquid bridge. Depending on particle concentration, percolating networks can form of rods wetted by the minority phase after temperature quenching such a system just across the binodal.

Mixing of miscible gas with oil in a reservoir decreases the effective strength of the gas, which can adversely affect miscibility and recovery efficiency. The mixing that occurs in a reservoir, however, is widely debated and often ignored in reservoir simulation, where very large grid blocks are used. Large grid blocks create artificially large mixing that can cause errors in predicted oil recovery. Reservoir mixing, or dispersion, is caused by diffusion of particles across streamlines of varying velocities. Mixing is enhanced by any mechanism that increases the area of contact between the gas and the oil, thereby allowing the effects of diffusion to be magnified. This is, in essence, the cause of scale-dependent dispersion. The contact area grows primarily because of variations in streamlines and their velocities around grains and through layers of various permeabilities (heterogeneity). Mixing can also be enhanced by crossflow, such as that caused by gravity and by the effects of other neighboring wells. This dissertation focuses on estimation of the level of effective local mixing at the field scale and its impact on oil recovery from miscible gas floods. Pore-level simulation was performed using the Navier-Stokes and convection-diffusion equations to examine the origin of scale dependent dispersion. We then estimated dispersivity at the macro scale as a function of key scaling groups in heterogeneous reservoirs. Lastly, we upscaled grid blocks to match the level of mixing at the pattern scale. Once the contact area ceases to grow with distance traveled, dispersion has reached its asymptotic limit. This generally occurs when the fluids are well mixed in transverse direction. We investigated a variety of pore-scale models to understand the nature of scale dependency. From the pore-scale study, we found that reservoir mixing or dispersion is caused by diffusion of particles across streamlines. Diffusion can be significantly enhanced if the surface area of contact between the reservoir and injected fluid are increased as fluids propagate through the reservoir. Echo and transmission dispersivities are scale dependent. They may or may not reach an asymptotic limit depending on the scale of heterogeneities encountered. The scale dependence results from an increase in the contact area between solute (gas) and resident fluid (oil) as heterogeneities are encountered, either at the pore or pattern-scale. The key scaling groups for first-contact miscible (FCM) flow are derived and their impact on mixing is analyzed. We examine only local mixing, not apparent mixing caused by variations in streamline path lengths (convective spreading). Local mixing is important because it affects the strength of the injected fluid, and can cause an otherwise multicontact miscible (MCM) flood to become immiscible. We then showed how to upscale miscible floods considering reservoir mixing. The sum of numerical dispersion and physical dispersion associated with the reservoir heterogeneities, geometry and fluid properties must be equal at both the fine- and large-scales. The maximum grid-block size allowed in both the x- and z-directions is determined from the scaling groups. Small grid-blocks must be used for reservoirs with uncorrelated permeabilities, while larger grid blocks can be used for more layered reservoirs. The predicted level of mixing for first-contact miscible floods can be extended with good accuracy to multicontact miscible (MCM) gas floods. / text

This thesis describes experimental studies of colloidal particles dispersed in solvents which themselves have phase transitions. One common definition of soft matter is: a material characterized by a mesoscopic length scale. This length scale is, for example, the colloid size or the ordered domain size. Here we combine a complex host with one characteristic length scale with dispersed particles that have a different size. It might be anticipated that new behaviour will occur. Two limits of particle characteristics are probed: the case of dilute sterically-stabilized particles and the case of a weak gel of attractive particles. The two systems are polymer particles dispersed in a phaseseparating microemulsion and silica nanoparticles dispersed in a low molecular weight liquid crystal. In each system a temperature driven phase transition plays a crucial role. In the microemulsion case we observe how transitional and pre-transitional phenomena create effective interactions between particles and how new behaviour emerges in the host solvent in the late stage of the phase separation. We show that the pre-transitional clustering of the PMMA particles is due to an adsorbed layer of dodecane. Subsequently heterogeneous nucleation of the gas phase is seen. After phase separation has occurred in off-critical samples the particles remain in either the continuous or dispersed phase depending on the original microemulsion composition. In the late stage of the phaseseparation the coalescence and coarsening behaviour changes significantly, after more material exchange between the phases has taken place. This behaviour is reminiscent of viscoelastic phase separation in polymer based samples. In the liquid crystal case we discover the anisotropy of the liquid crystal persists over large length scales and modifies the local dynamics of the gel. Using electron microscopy and scattering techniques we demonstrate that the silica embedded in the liquid crystal forms agglomerates with a fractal structure. Rheological characterization demonstrates that the resulting composite is a gel. Investigation of the composite’s local dynamics using x-ray photon correlation spectroscopy shows anisotropy and intermittency in the dynamics on significant length scales. In both systems we have studied new behaviour seen due to the influence of one component on the dynamic characteristics of the other The pre- and post- phase transition phenomena are only crucial in the microemulsion case where the particles have purely repulsive interactions. Our results illustrate the subtle balances that occur in soft composite systems.

Com a atual preocupação ambiental e a necessidade de se conhecer os processos que regem o movimento da água e de solutos no solo, são necessários estudos que possibilitem aumentar a eficiência do uso de insumos no setor agrícola, que de certa forma possam mitigar o impacto das atividades deste setor sobre contaminação de águas subterrâneas. Portanto, objetivou-se com a presente pesquisa verificar os parâmetros de transporte do íon nitrato, diante de uma análise da influência dos respectivos íons acompanhantes, a partir de fontes distintas de nitrato, em seu deslocamento, com a elaboração de curvas de distribuição de efluentes (Breakthrough Curves (BTC)), em condições de amostras de solo deformadas e indeformadas. O trabalho foi realizado em condições de solo saturado e regime permanente, via aplicação de uma solução de nitrato na concentração de 50 g m-3 de NO3 -, por três diferentes fontes (Ca(NO3)2, NH4NO3 e KNO3), para dois tipos distintos de solos tropicais: Latossolo Vermelho Amarelo e Nitossolo Vermelho. O experimento foi conduzido no Laboratório de Solos e Qualidade de Água, do Departamento de Engenharia de Biossistemas da Escola Superior de Agricultura \"Luiz de Queiroz\", em Piracicaba - SP. Os parâmetros de transporte do íon nitrato na concentração de 50 g m-3 nos respectivos solos foram obtidos por um ajuste numérico utilizando-se o software STANMOD. Pelos resultados obtidos, pôde-se verificar que o deslocamento do nitrato está atrelado com as caraterísticas dos solos e que houve maiores efeitos de lixiviação para o Nitossolo Vermelho. Em termos da influência dos cátions acompanhantes do nitrato, em suas diferentes fontes distintas, pode-se dizer que não foram observados seus efeitos na mobilidade do nitrato no perfil do solo. / With the current environmental concerns and the need to understand the processes that govern the movement of water and solutes in soil, studies are needed to allow increasing the efficiency of input use in agriculture that somehow can mitigate the impact of activities of this sector on groundwater contamination. Therefore, the objective of this work was to verify the transport parameters of the nitrate, by analyzing the influence of the accompanying cation on nitrate displacement, through the development of distributions curves of effluents (Breakthrough Curves (BTC)), under conditions of disturbed and undisturbed samples in saturated soil and steady state conditions, via application of nitrate solution at a concentration of 50 g m-3 NO3 -, by three different sources (Ca(NO3)2, NH4NO3 and KNO3) and for two types of tropical soils: Yellow Oxisol and Anfisol. The experiment was conducted in the Laboratory of Soil and Water Quality, Department of Biosystems Engineering from Escola Superior de Agricultura \"Luiz de Queiroz\", Piracicaba - SP. The transport parameters of the nitrate at a concentration of 50 g m-3 in their respective soils were obtained by a numerical fit using the software STANMOD. From the results, it could be seen that the nitrate displacement is linked with the soil characteristics and the leaching was higher in Anfisol. In terms of the influence of accompanying cations of nitrate, in its various different sources, it can be said that their effects were not observed in nitrate mobility in the soil profile.

Extensive research has been carried out in both field and laboratory to explain water and solute movement under both saturated and unsaturated conditions. The importance of such work is obvious, since any attempt at exploring land reclamation by leaching or nutrient movement in plant feeding (to name only two) is subject to interpretations and theories of moisture flow. Water flow through soil during reclamation by leaching can be termed miscible displacement since soil water and leaching water do not have a distinct fluid-fluid interface and will physically mix. It is probable that miscible displacement investigations can contribute to an understanding of time-ion concentration relationships in land drainage. Much work is and has been done in the laboratory on moisture flow with particular reference to miscible displacement theories. This project investigates a portion of the overall miscible displacement phenomena in the field under conditions which would exist in practice. Specifically, an attempt is made to determine the relative importance of hydrodynamic dispersion and diffusion in a tile drained soil over a relatively impermeable clay using chloride as a tracer.

A mathematical model was developed to predict the exchange of one cation by another in a soil column undergoing one dimensional cation solution displacement under steady state flow conditions. The model allowed prediction of both the solution and exchanger phase concentration of the cation in question. The model consists of a material balance equation which is a parabolic type partial differential equation. The assumption was made that equilibrium was reached instantaneously between the cations in the solution phase and the exchanger phase. This assumption reduced the material balance equation to a form that allowed numerical solution providing the data concerning the cation exchange isotherm and the initial and boundary conditions are available. FORTRAN programs were written for the numerical computation of the problem involved. The computation was done on a digital computer. The model was verified by comparing the theoretically computed cation concentration profile with data from actual soil column experiments. The cation exchange of Mg→Ca was tested on Yolo fine sandy loam, Nibley clay loam and Haford Sandy loam columns. The exchange of Na→Ca was also tested on Yolo fine sandy loam. Satisfactory agreement between the column experiment values and the theoretically computed values was obtained.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 214-220). Available also in a digital version from Dissertation Abstracts.

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