Orientadores: Maria Amélia Novais Schleicher, Lúcio Tunes dos Santos / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matemática Estatística e Computação Científica / Made available in DSpace on 2018-08-25T10:12:39Z (GMT). No. of bitstreams: 1 Kamioka_DanielaMidori_M.pdf: 9312784 bytes, checksum: cd5e7b440a4b44168749d7cc069f1ac0 (MD5) Previous issue date: 2014 / Resumo: Uma das principais etapas do processamento sísmico é a análise de velocidade. Essa é uma das técnicas que utilizam dados sísmicos organizados em famílias de ponto médio comum (CMP ¿ Common Midpoint). Encontrar curvas (por exemplo, hiperbólicas) pré-determinadas que se ajustam aos tempos de trânsito de reflexão da melhor maneira possível é de grande importância no processo CMP. Além disso, é necessário determinar corretamente os parâmetros que definem essas curvas de melhores ajustes, pois estes parâmetros transmitem informações importantes a serem extraídos dos dados sísmicos. Portanto, é essencial uma medida que estabeleça se certa curva se ajusta aos tempos de trânsito. A função semblance mede o grau de coerência (ou alinhamento) dos traços sísmicos ao longo das curvas testadas. A semblance convencional é uma medida robusta e fácil de ser calculada, e por esses motivos tem sido a mais utilizada dentre outras medidas. Além da função convencional, aplicamos outros dois tipos de funções: a Semblance com Peso e a Semblance AB. Os exemplos numéricos desse trabalho mostram que a medida de coerência com peso exibe uma melhor resolução no sentido de que as seções apresentam picos mais destacados com relação à semblance convencional, mas pelo fato dos valores obtidos pelas duas funções serem semelhantes e o custo computacional do cálculo da medida com peso ser bem superior à convencional, o esforço não vale a pena. Já a semblance AB tenta ser superior à convencional uma vez que para dados que apresentam um trend de amplitude (reversão de polaridade), a função AB apresenta uma pequeno aumento nos seus valores na região de reversão em questão, mas nada significativo, pelo menos nos exemplos de seção CMP utilizados nessa dissertação. Apesar de todas as tentativas de se obter uma medida de coerência que apresente melhores resultados com um baixo custo computacional, ainda assim a semblance convencional continua a apresentar resultados semelhantes aos outros métodos e com o menor tempo computacional para o seu cálculo / Abstract: One of the main steps of seismic processing is the velocity analysis. This is one of the methods that uses seismic data arranged in common midpoint (CMP) gathers. Finding predetermined curves (such as hyperbolic ones) that fit the reflection traveltimes the best possible way is of great importance in the CMP process. Moreover, it is necessary to correctly determine the parameters that define those best-fitting curves, as these parameters convey important information to be extracted from seismic data. Therefore, it is essential to establish a measure that determines if any curve fits the travel time. The semblance function is such a measure that determines the degree of coherence (or alignment) of the seismic traces along trial curves. Conventional semblance is a robust and easy-to-calculate measure, and for these reasons it has been the most used among other measures. Recently, two variations of semblance have been proposed in the literature: Weighted Semblance and AB Semblance. In this thesis, we show by means of numerical examples that Weighted Semblance provides better resolution in the sense that the semblance sections present more pronounced peaks than conventional semblance. However, the values obtained by the two functions are rather similar and the computational cost of calculating the weighted measure is much higher. Therefore, the effort is not worth it. AB semblance tries to be superior to the conventional function for data presenting an amplitude trend (for example, a polarity reversal). In our numerical tests, the AB function indeed provides a small increase in its values in the region of a polarity reversal, but nothing significant, at least for the CMP section examples used in this dissertation. Despite all attempts to obtain a coherence measure that offers better results with a low computational cost, conventional semblance still maintains similar results to other methods and the lowest computational time for its calculation / Mestrado / Matematica Aplicada / Mestra em Matemática Aplicada

Orientadores: Joerg Dietrich Wilhelm Schleicher, Maria Amélia Novais Schleicher / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação Científica / Made available in DSpace on 2018-08-19T06:03:21Z (GMT). No. of bitstreams: 1 Amaro_BrunoDias_M.pdf: 4962738 bytes, checksum: a4af95a3c26d6474e07216773530662e (MD5) Previous issue date: 2011 / Resumo: Em uma migração sísmica, após o processo de propagação da onda, um importante passo para se obter uma imagem migrada é a aplicação de uma condição de imagem, que distingue entre pontos refletores e não refletores. A condição de imagem teórica desenvolvida por Claerbout usa uma deconvolução entre os campos de ondas descendente e ascendente (ou uma divisão no domínio da frequência). Uma vez que não conhecemos a posição real do refletor, esta divisão precisa ser executada em todos os pontos da imagem, causando uma certa instabilidade no processo, já que o campo de onda descendente é igual a zero em determinados pontos do meio. Pensando em tentar solucionar esse problema, diferentes técnicas de estabilização foram propostas, sendo a primeira uma correlação ao invés da deconvolução teoricamente exigida. Entretanto este processo destrói as informações de amplitude contidas nos dados. Como fica cada vez mais importante fornecer compensação de iluminação e preservação de amplitudes, particularmente, se o objetivo é recuperar com sucesso uma refletividade do meio, uma condição de imagem que destrói amplitudes é inaceitável. Por esta razão, várias formas alternativas de condições de imagem têm surgido nos últimos anos, que são avaliadas pela qualidade das amplitudes e artefatos produzidos. Neste trabalho estudamos uma série de condições de imagem com compensação de iluminação. Apresentamos também novas condições de imagem por quadrados mínimos estabilizados e as comparamos com as condições de imagem anteriormente propostas. Nossos experimentos numéricos em um simples modelo horizontal que utiliza um modelo de velocidade vertical não homogêneo e no dado Marmousi mostram que tais condições produzem resultados satisfatórios. Uma observação geral sobre todas as comparações feitas é que a condição de imagem por quadrados mínimos totais estabilizados que zera os pontos da imagem onde o denominador é de baixo valor produziu a melhor imagem com o mínimo de artefatos de migração e o mínimo de amplitudes de migração afetados. A qualidade desta imagem chega muito próximo da simples condição de imagem por correlação / Abstract: In a seismic migration, after the wave propagation process, an important step to obtain a migrated image is the application of an image condition, that distinguishes between reflector and non reflector points. The theoretical imaging condition addressed by Claerbout uses a deconvolution between downgoing and upcoming wavefields (or a division in the frequency domain). Since we do not know the actual position of the reflector, this division must be performed at all points of the image, causing instability in the process, since the downgoing wavefield is zero at certain points. Trying to remedy this problem, different stabilization techniques have been proposed, being the first a crosscorrelation rather than the theoretically required deconvolution. However, this process destroys the information contained in the data amplitudes. As it becomes increasingly important to provide compensation for illumination and amplitude recovery, particularly, if the goal is to successfully recover a reflectivity of the medium, a condition that destroys the image amplitude is unacceptable. For this reason, several alternative forms of imaging conditions have emerged in the recent past that are evaluated by the quality of the output amplitudes and artifacts produced. In this work we study a set of imaging conditions with illumination compensation. We also present new stabilized least-squares image conditions and compare them to previously proposed forms. Our numerical experiments on a simple horizontal interface model using a vertically inhomogeneous velocity model and on the Marmousi data set show that they produce satisfactory results. The general observation from the overall comparison is that the stabilized total least-squares imaging condition produced the best image with the least migration artifacts and the least affected migration amplitudes. Its image quality comes very close to the one of the simple crosscorrelation imaging condition, however with correctly preserved amplitudes / Mestrado / Matematica Aplicada / Mestre em Matemática Aplicada

Orientador: Martin Tygel / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências / Made available in DSpace on 2018-08-21T00:35:26Z (GMT). No. of bitstreams: 1 FaccipieriJunior_JorgeHenrique_M.pdf: 11845729 bytes, checksum: 1c69f6a509b40bc499fe38630fb28be9 (MD5) Previous issue date: 2012 / Resumo: O método de empilhamento Common Reflection Surface (CRS) permite obter seções de afastamento nulo simuladas de maior qualidade e extrair um maior número de atributos que caracterizam o meio geológico que o tradicional método de empilhamento Common Midpoint (CMP)...Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital / Abstract: The Common Reflection Surface (CRS) method is able to obtain simulated zero-offset sections of higher quality and the extraction of a greater number of attributes which characterize the geological medium than the traditional Common Midpoint (CMP) method...Note: The complete abstract is available with the full electronic document / Mestrado / Reservatórios e Gestão / Mestre em Ciências e Engenharia de Petróleo

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / Microfiche copy available in Archives and Science. / Bibliography: leaves 229-245. / by Peter David Efran Goreau. / Sc.D.

Approximately 9.5 km of seismic reflection data over the western margin of the Sanford Triassic Basin in North Carolina were acquired by Chevron, Inc. in 1972. These data enabled a comparison of the relative effectiveness of dynamite and vibroseis sources to be made. A comparison of 3-fold and 12-fold dynamite data, as well as 24-fold vibroseis data with a relatively limited bandwidth, indicate that frequency content of the source used in seismic surveys over Triassic basins is more critical in determining the quality of the stacked data than subsurface coverage. The use of an automatic line drawing routine proved useful in delineating the subsurface geometry of the basin. Available well data were used in conjunction with the seismic data to locate the Cumnock (coal-bearing) Formation within the basin and construct a geologic section across the study area. Strong reflections from the bottom of the basin were recorded. Reflections from beneath the basin ( > 0.7 sec) are attributed to meta volcanics and mylonites of the Carolina Slate Belt. / M.S.

Velocity anisotropy is present at a point in a medium if the seismic velocity in one direction in general differs from that in another direction. The problems associated with the determination of subsurface velocity in anisotropic media by the use of surface seismic reflection data are analyzed. Previous studies of anisotropy in exploration seismology required bore-hole data as well as surface data to detect the presence of velocity anisotropy. Three special types of wave propagation are of interest in reflection seismology, in addition to the general case. The theory of isotropic media is commonly utilized in exploration seismology. Elliptical anisotropy has been the method for handling anisotropic media in the past. The theory of transversely isotropic media is studied in detail since this is a reasonable anisotropy model for exploration use. Layered periodic isotropic structures are considered because of the relationships between the elastic coefficients that yield transverse isotropy in the limiting case for which the isotropic lavers are thin in comparison to the wavelength of a propagating disturbance. Synthetic common-depth-point reflection seismic traces were generated for a uniformly anisotropic halfspace, a model with seismic velocity increasing linearly with depth, velocity increasing stepwise with depth, a buried anisotropic interval in an otherwise isotropic section, and models characterized by the dip varying continuously with depth. Correlation methods (velocity analysis) are developed for the determination of rms velocity vs. two-way reflection time for both isotropic and anisotropic (transversely isotropic) media. These methods are applied to the models discussed above for varying amounts of anisotropy for each model. When the surfaces defined by the velocity analysis correlation matrices are integrated to determine the volume under the surface, it is possible to determine within about one percent the degree of anisotropy in a uniformly anisotropic medium. In a medium of varying anisotropy, it does not appear possible to obtain the same degree of accuracy as for the uniform case. Two isotropic dipping layer models were studied to determine the effects of dip on velocity analysis. The effects of dip are such that the analysis methods yield erroneous results for dips in excess of about 10-12 degrees for the models studied. Random noise degrades the velocity analysis (i.e., the magnitudes of the correlation peaks), but does not affect the accuracy of the results. Lateral velocity gradients appear to have no discernible effects on a velocity analysis for the models studied. Results of this study indicate that the compressional wave data normally used in reflection seismic work may not be useful for the detection of velocity anisotropy. Shear wave (SV) data, on the other hand, are ideally suited to this purpose. Hmvever, the necessity of shear wave data for the detection of anisotropy may limit these methods strictly to land use. This study indicates that the probability of detecting anisotropy by using surface methods is sufficiently high to warrant field testing. / Ph. D.

Reflection seismic data were acquired (by CONOCO, Inc.) which targeted known channel interruption of an upper Pennsylvanian coal seam (Herrin #6) in the Illinois basin. The data were reprocessed and interpreted by the Regional Geophysics Laboratory, Virginia Tech. Conventional geophysical techniques involving field acquisition and data processing were modified to enhance and maintain high frequency content in the signal bandwidth. Single sweep processing was employed to increase spatial sampling density and reduce low pass filtering associated with the array response. Whitening of the signal bandwidth was accomplished using Vibroseis whitening (VSW) and stretched automatic gain control (SAGC). A zero-phase wavelet-shaping filter was used to optimize the waveform length allowing a thinner depositional sequence to be resolved. The high resolution data acquisition and processing led to an interpreted section which shows cyclic deposition in a deltaic environment. Complex channel development interrupted underlying sediments including the Herrin coal seam complex. Contrary to previous interpretations of channel development in the study area by Chapman and others (1981), and Nelson (1983), the channel has been interpreted as having bimodal structure leaving an"island" of undisturbed deposits. Channel activity affects the younger Pennsylvanian sediments and also the unconsolidated Pleistocene till. A limit to the eastern migration of channel development affecting the the Pennsylvanian sediments considered in this study can be identified by the abrupt change in event characteristics. / Master of Science

Large amplitude seismic reflections from within the Catoctin Formation of central Virginia are interpreted to originate from acoustically thin beds of interlayered metabasalts and metasediments. Large acoustic impedance contrasts exist between epidotised layers ( epidosites and volcanic breccia) and non-epidotised layers (greenstones and phyllites) within the Catoctin Formation. Acoustic impedance contrasts also exist between greenstones (metabasalts) and phyllites (metasediments). Constructive interference of small amplitude reflections from thin beds result in large amplitude, reverberating reflections. Thin bed reflections that approximate the first derivative of the source wavelet constructively interfere to give even larger amplitude reflections than those originating by conventional tuning. Computer modeling based on two geologic sections of thin beds of epidosites interlayered with greenstones and of greenstones interlayered with phyllites and epidosites indicates that large amplitude reflections result from constructive interference of thin bed reflections. / Master of Science

Sonic wave methods can be used to provide information on the engineering properties of rocks. The advantages of such techniques include minimal sample preparation, fast site preparation for field tests, reproducible and nondestructive tests, and capability for large scale testing. During this research an extensive review of the most widely accepted engineering rock classification systems was undertaken and their principles, advantages and disadvantages are presented in detail. The mathematical equations describing wave propagation through elastic and viscoelastic media are analyzed in order to determine the dynamic parameters most likely related to static properties. A detailed description of the instrumentation and experimental procedures used for sonic testing is presented. Based on the experimental data, a correlation between the most characteristic static and dynamic properties was established. These relationships can be used to modify existing engineering rock classification systems, by appropriately substituting static properties by the much easier to measure, in the field and in the laboratory, sonic wave parameters. Furthermore, a classification scheme was developed, incorporating information pertaining to the static modulus of elasticity and frequency of joints from sonic wave information. / Master of Science

Approximately 37 km of predominantly 24-fold P-wave Vibroseis data and 16 km of 24-fold SH-wave Vibroseis data were acquired in the southern portion of the folded Appalachians near the Bane Dome in Giles County, Virginia. Data processing techniques included the application of newly developed methods for crossdip removal as well as the determination of statics solutions in the case of time variant shifts within the data traces. Minimum-phase filter deconvolution was also applied for the removal of reverberating energy and multiples recorded on the SH—wave lines. V_p/V_s ratios were used to aid in the determination of lithologies in the absence of bore-hole data. Interpreted thickening of the Lower Cambrian to Upper Precambrian sequence beneath the Bane Dome appears to represent Eocambrian rifting. Faults generated at that time may now be reactivated by the present stress regime, causing earthquake activity in this area. Interpretation of the seismic data supports a duplex structure proposed for the Paleozoic rocks of the Bane Dome Complex within the Narrows thrust sheet of southwestern Virginia. / Ph. D.