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Carbonate and sandstone reservoirs play an important role in oil industry as they host over 50% of the world’s hydrocarbon reserves. For an accurately assessment of porosity and pore size distribution of such complex pore-network, which affect directly the macroscopic characteristics of multiphase fluid flow, X-ray computed microtomography (micro-CT) emerges as a powerful tool. In contrast to lab-based X-ray micro-CT (XCT), synchrotron X-ray micro-CT (SXCT) images are commonly free of artefacts (i.e. beam hardening) and the unique properties of synchrotron sources enable the X-ray imaging of complex and heterogeneous materials in greater detail, with higher quality, and short acquisition time. This work reports results of cone beam computed microtomography (XCT) in comparison with synchrotron computed microtomography (SXCT) applied to very heterogeneous carbonate and sandstone reservoir rocks. We analyze the quality of the image generated in terms of detection of details and artefacts, the advantages and limitation of each technique, as well as features like contrast, sharpness, and signal-to-noise ratio (SNR). Although SXCT offers significant advantages over XCT, the latter gains in cost of operation, accessibility and user-friendliness.

Innovative solutions have been designed to meet the global demand for energy and environmental sustainability, such as enhanced hydrocarbon recovery and geo-sequestration of CO2. These processes involve the movement of immiscible fluids through permeable rocks, which is affected by the interfacial properties of rocks at the pore scale. Overcoming major challenges in these processes relies on a deeper understanding about the fundamental factors that control the rock wettability. In particular, the efficiency of oil recovery strategies depends largely on the 3D wetting pattern of reservoir rocks, which is in turn affected by the adsorption and deposition of ‘contaminant’ molecules on the pores’ surface. Here, we combined high-resolution neutron tomography (NT) and synchrotron X-ray tomography (XRT) to probe the previously unobserved 3D distribution of molecular and mineralogical heterogeneity of oil reservoir rocks at the pore scale. Retrieving the distribution of neutron attenuation coefficients by Monte Carlo simulations, 3D molecular chemical mappings with micrometer dimensions could be provided. This approach allows us to identify co-localization of mineral phases with chemically distinct hydrogen-containing molecules, providing a solid foundation for the understanding of the interfacial phenomena involved in multiphase fluid flow in permeable media.

This article studies the individual contribution of each term in the Navier-Stokes-Darcy (Brinkman) equation to the fluid linear momentum balance and the consequences of opting for the Darcy or Brinkman equations in 3D reactive flow simulations of a vuggy carbonate. A two-scale continuum model was used to simulate the acidification of a carbonate sample using the Darcy and Brinkman equations. Rock heterogeneity is considered in the initial porosity and permeability fields, which are calculated directly from micro-CT images. Simulations showed that the Darcy equation predicts the acid breakthrough earlier in most cases. The convective acceleration term in the Brinkman equation plays an important role in describing the fluid momentum balance at high injection velocities, and this is a clear evidence against the use of the Darcy equation to model reactive flow in such conditions.

CO2 reinjection in petroleum reservoirs brings advantages in oil production but may cause dissolution in carbonate reservoirs. Two-scale continuum models have been successfully used to simulate acidification. However, the use of realistic porosity and permeability fields in mesh simulations is still a challenge, in such a way that uniform and normal distributions have been used to generate these fields in the past. The main objective of this work was to transcript the plugs heterogeneity from the micro-CT images to simulation. The porosity field was calculated directly from micro-CT images, and two methodologies are proposed to calculate the permeability field. A reactive two-scale continuum solver was implemented in OpenFOAM and used to simulate reactive flow in two carbonate samples with different intrinsic reaction rates (calcite and dolomite). The experimental permeability evolution curves, as well as wormholes shapes and paths, are reproduced in the simulations. We observed a critical influence of specific surface area, reaction rate constant, and initial permeability field for the simulations of acidification processes.

Aços elétricos têm sido amplamente utilizados na construção de motores e transformadores por apresentarem menores perdas energéticas quando comparados aos aços comuns. Desde a segunda metade do século XX, os aços elétricos de grão orientado vêm apresentando eficiências cada vez maiores e, portanto, com etapas de produção cada vez mais elaboradas e necessitando de controles mais rigorosos. No processo de fabricação de tais aços, diferentes compostos são precipitados na matriz do aço e empregados como inibidores de crescimento de grão. Dentre esses inibidores, se destacam o sulfeto de manganês e o nitreto de alumínio, que, ao impedirem o crescimento dos grãos ferríticos na recristalização primária, promovem o acúmulo de energia necessário para que a recristalização secundária ocorra, etapa em que o crescimento dos grãos com a chamada textura Goss é favorecida. Nesse trabalho, foi estudada a precipitação de AlN em aços elétricos de grão orientado. O trabalho engloba uma discussão dos processos termodinâmicos e cinéticos envolvidos na precipitação através da modelagem de vários parâmetros, como energia livre de Gibbs envolvida no processo de precipitação, influência da energia interfacial e efeitos de precipitação em contornos de grãos e em deslocações. Foram construídos diagramas PTT para o processo de precipitação, na faixa de temperatura entre 500ºC e 1300ºC. Foram comparados dois modelos para a avaliação da influência da energia elástica da matriz na precipitação e um modelo que trata simultaneamente a nucleação e crescimento de precipitados em matrizes ferríticas. Por fim, os dados encontrados foram comparados com os dados obtidos da literatura a fim de se avaliar a validade da dissertação, e a conclusão foi que esta é capaz de prever, com razoável precisão, os dados experimentais reportados na literatura. Electrical steels have been widely used in the construction of motors and transformers because of the lower energy losses when compared to common steel. Since the second half of the twentieth century, grain-oriented electrical steels have been achieving increasing efficiencies, and therefore its production phases have become more elaborate, thus, needing tighter control. In the manufacture of such steels, different compounds are precipitated in the matrix of the steel and used as grain-growth inhibitors. Among these inhibitors, special attention has been given to manganese sulfide and aluminum nitride, which, by preventing the growth of ferritic grains in the primary recrystallization, promote the accumulation of energy required for the secondary recrystallization process to occur, when the growth of grains having Goss texture is favored. In this work, the precipitation of AlN in grain-oriented electrical steels has been studied. The work includes a discussion of the thermodynamic and kinetic processes involved in precipitation through the modeling of various parameters, such as Gibbs free energy in the precipitation process, influence of interfacial energy and effects of precipitation in grain boundaries and in dislocations. PTT diagrams were constructed for the precipitation process in the temperature range between 500ºC and 1300ºC. Two models for assessing the influence of elastic energy matrix in precipitation and a model that treats both the nucleation and growth of precipitates in ferritic matrices were compared. Finally, the obtained data were compared with those obtained from the literature in order to assess the validity of the thesis and the conclusion was that it is able to reach, with reasonable accuracy, the experimental data reported in the literature.