4,012 research outputs found
Pore structure characterization of low permeability rocks
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2014.Hoje as pesquisas em rochas de baixa permeabilidade (grande tendência no mundo e em breve na indústria petrolífera brasileira) se voltam à escala de poros seja para investigação petrofísica, morfológica, de distribuição de tamanhos de grãos ou poros ou escoamento de fluidos, prática descrita pelos valores de permeabilidade. A avaliação destas propriedades por sua vez, é essencial ao desenvolvimento e exploração de reservas de hidrocarbonetos. No entanto, a determinação de parâmetros do sistema poroso nessas rochas, arenitos de baixa permeabilidade (TGS) e rochas selantes (SR), continua a ser um grande desafio devido à extrema variabilidade de ambientes deposicionais e complexa microestrutura composta por argilas e tamanhos de poros de submícrons a ångströms. Nesta tese empregou-se um conjunto de técnicas experimentais para a caracterização da estrutura porosa de TGS e SR. De tal modo, o trabalho foi dividido em dois tópicos principais: (i) Caracterização do sistema poroso e propriedades petrofísicas em TGS utilizando-se as técnicas de permeabilidade por decaimento de pulso (PDP), NMR de baixo campo, adsorção gasosa N2 (N2GA), porosimetria por intrusão Hg (MICP), nano- e microtomografia de raios X (res. Abstract : Nowadays, significant research effort in low-permeability rocks (a wide tendency elsewhere and soon in the Brazilian petroleum industry) has been focused on pore-scale petrophysics, morphologies and distributions, as well as fluid flow circulation described by the values of permeability. The evaluation of these properties in turn is essential for the assessment and exploitation of hydrocarbon reserves; however, determining pore system parameters in such rocks as tight gas sandstones (TGS) and seal rocks (SR) remains challenging because of the extreme variability in depositional environments resulting in complex pore structures comprised by clays and length scales from sub-microns to Angstroms. In this work we applied a set of techniques to characterize submicron-pore structures in TGS and SR. Therefore it was divided into two main topics of interest: (i) Characterization of petrophysical properties and pore systems in very low permeability TGS using Pulse-Decay Permeability (PDP), Low Field Nuclear Magnetic Resonance (LFNMR), Nitrogen Gas Adsorption (N2GA), Mercury Intrusion Capillary Pressure (MICP) and Multi-scale 3D X-ray Nano- and MicroCT (down to 0.7 µm resolution) techniques; (ii) Study of Photoacoustic Spectrometry (PAS) for determining thermal diffusivity (TD) and porosity in three seal rocks originating from dissimilar fields as a key issue for safe exploration, storage purposes (CO2 sequestration) and developments in shale characterization. The values obtained for TD were between 0.01667 and 0.09298 (cm2/s) while porosity ranged from 1.42 to 9%. For the analyzed TGS the 3D pore-structure characterization lead to pore tortuosity and shape factors ranges of 2.19-5.47 and 3.2-8.5, respectively, and pore size distributions tended to be bimodal for MICP, trimodal for 3D multi-scale and tetramodal for LFNMR measurements. The porosity values ranged from 1.94 to 11.96% obtained by the combination of N2GA and MICP techniques and permeability from 0.036 to 0.00066 mD by PDP technique. The measured pore-structure parameters were also used to predict empirical permeability in TGS (using e.g. Carman-Kozeny (Dullien, 1992) and Coates (1999) models). The set of applied methods has shown to be a useful tool for the unconventional reservoir characterization since it allows obtaining pore morphological and quantitative parameters which account for the permeability values
The provenance of the norber erratics, and the formation of post-devensian-deglaciation pedestal rocks with carboniferous limestone pedestals in England, Ireland and Wales
No full textThis study investigates a Devensian glacial conundrum, the provenance of the Norber erratics in North Yorkshire, and the
origins of a post-Devensian-deglaciation landform, pedestal rocks with Carboniferous limestone pedestals in England,
Ireland and Wales.
Investigations to determine the provenance of the Norber erratics were undertaken in a study area of about 2000ha. Mapping
erratic dispersal and measuring striae strike revealed that the provenance is Crummackdale, and that Devensian ice crossed
over only the Crummack, Sowerthwaite and Austwick formations en route to Norber. Petrographical and physical surveys
further revealed that the erratics are derived from the Austwick Formation only, and that provenance is a glacially-plucked
‘amphitheatre’ in the vicinity of the Old Limekiln (SD 770707).
Investigations to determine the formation of post-Devensian-deglaciation pedestal rocks with Carboniferous limestone
pedestals were undertaken at 19 sites in England, Ireland and Wales, where 162 pedestal rocks and a pedestal rock field
were examined. The study was divided into two, the formation of perched and mushroom pedestal rocks. An examination of
weathering and erosion processes at Norber, where only perched pedestal rocks with vertical sidewalls are found, revealed
that lowering of the inter-pedestal limestone surface has taken place primarily in a sub-regolith karstic environment, and
that little or no pedestal formation occurred prior to ca.10000BP. In contrast, the lowering of the inter-pedestal limestone
surface about perched pedestal rocks with sloping sidewalls, such as at Scales Moor (North Yorkshire) and the Burren
(County Clare), has taken place primarily in a subaerial environment. Moreover, pedestal formation commenced in
ca.14500BP in England and Wales, and ca.13700BP in Ireland. The pedestals of mushroom pedestal rocks have formed due
to lateral dissolution under regolith that has largely been eroded, probably following deforestation in ca.3000BP
The Role of Egr1 in Driving Sex-Specific Transcriptional Programs and Anxiety-Related Behavior
No full textWomen have a two-fold increased risk for anxiety and depression disorders compared to men, though the molecular mechanisms underlying this phenomenon are understudied. Clinical and epidemiological data indicate ovarian hormone fluctuations are a critical female-specific risk factor for these disorders. Accordingly, we previously demonstrated that anxiety-like behavior in female mice varies across the estrous cycle. We also showed estrous cycle-dependent changes in neuronal chromatin accessibility and gene expression in the ventral hippocampus, a region critical for emotion regulation in rodents. Analysis of these data identified Egr1, a transcription factor and estrogen-responsive immediate early gene product, as a candidate regulator of chromatin regulation and gene expression across the estrous cycle. To test this, in the current study, I first profiled behavior and Egr1 expression across the four estrous cycle phases, revealing that high-estrogenic proestrus females have lower anxiety indices. However, following the withdrawal of estrogen levels that characterizes the other phases, anxiety-related behavior increased. In parallel, I observed cycling Egr1 mRNA expression across the estrous cycle, following estrogen levels. To mechanistically link Egr1 to the estrous cycle-dependent behavioral and molecular phenotype, I performed AAV-mediated, neuronal-specific overexpression of Egr1 in the ventral hippocampus of intact-male and ovariectomized-female mice. I then performed anxiety- and depression-related behavioral tests, as well as cell type-specific genomics assays profiling neuronal chromatin (ATAC-seq) and gene expression (RNA-seq). Results from behavioral tests implicate Egr1 in driving cyclical changes in anxiety- and depression-related behaviors in females, with no effect of Egr1 overexpression in males, indicating the effect is sex-specific. Further, Egr1 overexpression induced sex-specific changes in gene expression and chromatin organization, including Egr1-directed chromatin opening, in ventral hippocampal neurons that give crucial insights into this behavioral phenotype, including female-specific regulation of genes related to serotonin and anxiety. Overlapping these data with the previously generated estrous cycle data demonstrated that Egr1-induced chromatin regulation facilitates the downregulation of anxiety-related genes and the upregulation of synaptic plasticity-related genes during the high-estrogenic proestrus phase. Taken together, these results causally link Egr1 to estrous cycle-dependent gene regulation and behavioral plasticity and establish a foundation for developing sex-specific treatments for anxiety and depression
Orientation-based Continuum Damage Models for Rocks
No full textA general formulation of the Helmholtz free energy used in thermodynamics of damage process of rocks is derived within a multi-scale framework. Such a physically-based thermodynamic state potential has a hybrid, discrete/continuum, nature in the sense th
The mineralogy, geochemistry, and petrogenesis of the grønnedal-íka alkaline igneous complex, south-west Greenland
No full textAt 1299±17 Ma (Blaxland et al, 1978), the Grønnedal-Íka is the oldest of the Gardar centres, situated in the extreme north-west of the province. Hare-earth clement (REE) trends suggest that the nepheline-syenites which make up the bulk of the complex were derived from a parental magma formed by a few percent of partial melting of a garnet-lherzolite mantle source during an episode of rifting in the Early Gardar. In contrast to other undersaturated Gardar centres, the syenites of Gronnedal-l'ka show some striking raineralogical differences. The scarcity of amphibole and lack of olivine indicate a magma with a relatively high oxygen fugacity. Opaque oxide compositions and pyroxene trends provide further support for this idea. Additionally, the occurrence of zircon in all units of the complex is unusual, and is probably related to post-magmatic alteration processes. Fractionation of apatite and zircon appears to have been responsible for the observed variations in REE content, although later iteration and variations in the composition of the inter- cumulus liquid have given rise to a considerable scatter in major and trace element abundances. Normative compositions show the evidence for the development of a 'sandwich' horizon in both the Lower and Upper Series. At a later stage, a plug of xenolithic syenite was intruded, which was followed by a the em placement of a body of xenolithic carbonatite, containing fragments of the earlier syenites. This unit is predominantly s0vitic, but with increasing fractionation, more iron-rich (ferrcarbonatite) compositions were developed. Compared to many carbonatites, the rock at Grønnedal is rather poor in 'exotic' minerals. Trace element abundances, however, show extreme enrichment in Sr, Th, REE's, and Y, and depletion in Zr, Ti, and K compared to the syenites. These variations are comparable to the observed concentrations in the Igaliko carbonatite dykes (Pearce, 1988). Hf, Ta, and REE distributions between the carbonatite and syenitic rocks suggest that the carbonatite was derived by liquid immiscibility from a Co(_2)-saturated phonolitic magma, with the conjugate silicate phase possibly intruded as the Xenolithic Porphyritc Syenite. Patchy metasomatic alteration has affected all units, and has given rise to the Coarse- Grained Brown Syenite, which occurs in both the Lower and Upper Series. More intense alteration has affected the syenites, giving carbonate-rich 'carbosyenites', and xenoliths of country rock within the syenites and carbonatite; the surrounding country-rock is not as severely affected as might have been expected. The presence of zircon, alkali mafics, sodalite veins, and recrystallisation of feldspar in the altered rocks is attributed to the effects of peradkaline. C1 and C0(_2)-rich late-stage fluids derived from both the syenites and carbonatite
Rapid solubility and mineral storage of CO2 in basalt
No full textThe long-term security of geologic carbon storage is critical to its success and public acceptance. Much of the security risk associated with geological carbon storage stems from its buoyancy. Gaseous and supercritical CO2 are less dense than formation waters, providing a driving force for it to escape back to the surface. This buoyancy can be eliminated by the dissolution of CO2 into water prior to, or during its injection into the subsurface. The dissolution makes it possible to inject into fractured rocks and further enhance mineral storage of CO2 especially if injected into silicate rocks rich in divalent metal cations such as basalts and ultra-mafic rocks. We have demonstrated the dissolution of CO2 into water during its injection into basalt leading to its geologic solubility storage in less than five minutes and potential geologic mineral storage within few years after injection [1–3]. The storage potential of CO2 within basaltic rocks is enormous. All the carbon released from burning of all fossil fuel on Earth, 5000 GtC, can theoretically be stored in basaltic rocks [4]
Umhlanga Rocks coastal defense
No full textThe eThekwini coastline is a vulnerable coastline subject to chronic erosion and damage due to sea level rise. In 2007 a severe storm caused major physical and economic damage along the coastline, proving the need for action. Umhlanga Rocks is a densely populated premium holiday destination on the eThekwini coastline suffering from similar problems due to its narrow beaches and lack of dunes in certain places. Interference with the coast of Umhlanga can entice fierce resistance from different groups of stakeholders, which makes finding a suitable solution more difficult. The above leads to the following problem definition: Due to erosion and extreme weather conditions the coastline of Umhlanga Rocks is shifting on shore, causing narrow beaches, decrease of tourism and increased risk of failures of the coastal structures. The current situation requires a new long term safety strategy, taking into account the social, economic and environmental vitality of the Umhlanga Rocks area as well. To solve the problem definition the main question states: How can the eThekwini municipality create a sustainable Umhlanga coastline while adding value to the area? To answer the main question many different elements, varying from conventional coastal protection measures to experimental ideas that would increase local business, were formulated during a brainstorm session. These elements are ranked on their cost, added value and technological feasibility. From the highest ranked elements in each category 11 different alternatives are created. By performing a multi criteria analysis these 11 alternatives are narrowed down to three alternatives and an additional `do nothing’ option is included. The do nothing option assumes that the beach will be completely gone in 30-40 years. It is further assumed Umhlanga Rocks recreational businesses are coupled to the beach and property values will drop by 12% once the beach is gone. This gives a NPV of R.15,000,000,000. It is suspected that the equilibrium that normally exists in the cross shore sediment transport is disturbed and more sediment moves offshore than onshore. The sill is designed to prevent the sediment form moving too far offshore and thus to create a new equilibrium. The bar retaining sill consists of prefab concrete elements located just outside the surf zone. From the Delft3D model it followed that the beach stays roughly the same size after construction of the sill. The NPV bases the cost of the sill on reference projects. With the beach maintaining its current size the total NPV amounts to R.116,000,000,000. The nourishment option adds enough sand to the beach to compensate for erosion and add 15 meters of beach according to the Delft3D model. It is assumed the nearby sand depot can be used to perform the nourishment. The nourishment itself will be done using a dredger connected to a floating pipeline to pump the sand to the beach. Shovels will be used to divide the sand over the beach area. The cost of the nourishment is based on the cost of a similar project, with the benefit of the added beach area the total NPV is R.142,000,000,000. The submerged breakwater creates a calmer wave climate near the coast and will thereby reduce erosion and increase beach growth. The Delft3D model suggests an average beach growth of 20 meters. For the breakwater design different materials are considered. Geotextile systems look very promising and have several advantages over a rock or concrete breakwater. A design with geotextile bags and one with geotextile tubes is made for the Umhlanga Rocks area. The NPV of the breakwater amounts to R.131,000,000,000. A second multi criteria analysis is performed to determine the overall best option. According to this analysis the construction of a submerged breakwater made of geotextile tubes provides the best solution to the problem from social and technical preferences. Social preferences include perceptions of stakeholders involved like environmental groups and property owners, but take the construction and maintenance costs of the alternative into account as well. In this case the geotextile tube breakwater uses conforming materials, does not cause any visual horizon pollution and seems to deliver the best benefits for the price involved. At the same time the results from the 3D simulations have shown that the breakwater is able to perform well on the technical preferences including the breakage of waves offshore and increase of beach width.Hydraulic EngineeringCivil Engineering and Geoscience
Synaptic plasticity in fronto-insular circuits underlying stress susceptibility and resilience
No full textChronic stress may trigger depressive episodes in vulnerable individuals but the underlying mechanisms remain incompletely understood. Converging lines of evidence indicate that these mechanisms may converge on the dysregulation of synaptic transmission in the anterior cingulate and anterior insula, disrupting motivation and hedonic function. In this review, we examine how chronic stress and antidepressants modulate synaptic connectivity in stress-sensitive brain circuits. We discuss the roles of various synaptic and molecular pathways in these processes, their interaction with circadian rhythms, and their contributions to the regulation of mood, with a particular focus on anhedonia. In the short term, stress effects on neuronal activity may be adaptive, but repeated engagement of these adaptations may lead to circuit dysfunction—a phenomenon known as allostatic load. We also highlight new insights from neuroimaging studies that suggest that synaptic reorganization within fronto-insular circuits that process valence, salience, and motivation could play a critical role in driving risk for depression and transitioning between mood states. We propose a working model in which synapse loss in the anterior cingulate and anterior insula may contribute to depression by disrupting effort valuation computations, which regulate decision making and hedonic function by integrating information about anticipated rewards and the effort required to obtain them
Modeling of inherent anisotropic behavior of partially saturated clayey rocks
No full textClayey rocks are frequently chosen as a geological barrier material for underground repositories. The inherent anisotropic mechanical behavior and the evolution of mechanical behavior with water content are two crucial material properties for the safety analysis of these structures. The present paper focuses on numerical modeling of the inherent anisotropy and the effect of water content, as well as the interactions of these properties in partially saturated clayey rocks with preferably oriented bedding planes. A discrete thermodynamic approach is adopted for describing the inherent anisotropic mechanical behavior, and the anisotropy of the elastic parameters, plastic evolution and damage evolution are considered. Capillary pressure is introduced to describe the effect of the water content with the help of the effective stress concept, and a procedure for the identification of the model parameters is presented. Finally, the proposed model is applied to a study of triaxial compression tests of argillite with different orientations of the bedding planes and variable water content. In summary, the main features of the studied material are well reproduced by the model
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