Directional seismic source signature deconvolution

Marine seismic source arrays are directional. Source directivity is used to attenuate coherent noise, but primary reflected data may be degraded. Source directivity is ignored in a standard processing sequence, so directional source signature deconvolution may be required. In the frequency-wavenumber (f-k) directional deconvolution method, a filter is calculated from far-field source signatures and is applied to the f-k transform of common-receiver gathers. Reflections on common-receiver gathers are often spatially aliased, and this causes practical problems with the technique. Directional deconvolution may also be performed in combination with prestack migration because the prestack Kirchhoff summation migration operator is a function of source take-off angle. The constant-offset section is deconvolved separately with a full range of filters for source signatures radiated in different directions; then the migration summation operator sums across the deconvolved sections, selecting the section which has been deconvolved for the correct source signature at each point. Physical model data, which were acquired over simple models using a directional source, are used to evaluate directional deconvolution assuming constant velocity. Reflector continuity and resolution are improved by using directional deconvolution. Directional deconvolution combined with prestack migration is extended to media in which the velocity varies with depth, and is applied to two datasets from the Southern North Sea. The second dataset, which has shallow steeply dipping reflectors, is improved by using directional deconvolution. Directional deconvolution may be combined with a Kirchhoff migration technique which assumes a linear velocity-depth model. Results are superior to conventional Kirchhoff migration because ray bending is honoured. Directional deconvolution cannot synthesise fully point-source equivalent data from data acquired with a source array without excessive noise amplification. Source arrays with a short in-line dimension should be used where possible. For data which have been acquired with a long source array, directional deconvolution is desirable

Seismic imaging of oceanic detachment faulting

We understand plate tectonics by understanding relative plate motion at the plate boundaries, and the processes occurring there. Diverging plate boundaries are classified according to their spreading rate, with two broad categories as fast or slow-spreading. While fast-spreading is considered dominantly a magmatic process, faulting is much more important during slow spreading, leading to a far rougher, more rugged and more three-dimensional seafloor morphology which together with the large acoustic impedance contrast between basement and seawater, presents a severe seismic imaging challenge, with scattering of energy by the rough seafloor, velocity distortions from the rugged seafloor and strong side-coming events from the three-dimensional topography. Overcoming these challenges is critical to determine the geometry, extent, and mechanics of the faults, including large offset normal faults, called oceanic detachment faults (ODFs). As their footwalls - known as oceanic core complexes (OCCs) - consist of plutonic gabbros and mantle rocks, the fault must root beneath the crust. Their dimensions in the spreading direction indicate large offset, together suggesting that ODFs locally take up much of the plate divergence, but key questions remain about their geometry, mechanics, and lateral extent. This thesis addresses these issues and the challenge of seismic imaging of slow-spread crust in the 13° N area of the Mid-Atlantic ridge through a study of two oceanic detachment faults (13°20’ N and 13°30’ N, shortened hereafter to 1320 and 1330). A processing scheme – consisting of downward continuation to collapse side-swipe diffractions, followed by amplitude muting to remove them, deconvolution and velocity filtering processes - was developed to allow 2D seismic data to resolve the fine structure of the detachments, to suppress side-coming events, to reveal the geometry of ODFs in depth, and to determine the lateral extent of the detachments and the interaction between neighbouring detachments. The fine structure of the ODF was resolved to be anastomosing subsurface features, consistent with the latest ideas for the origin of the corrugated surfaces. Depth imaging shows that ODF steepen smoothly downwards from the low-angle of the exposed OCC to dips of ~60° at depths of ~5km, projecting to the bands of micro-earthquakes observed, a geometry everywhere consistent with slip-angle allowed by rock mechanics. Finally, Imaging on four intersecting profiles outline the extent of the two ODFs (1320 and 1330) in the slip and isochron direction showing the 1320 ODF cuts across and deeper than the 1330, in agreement with micro-earthquake data that show it is active while 1330 is not but suggesting they could have been linked in the past

3D velocity-depth model building using surface seismic and well data

The objective of this work was to develop techniques that could be used to rapidly build a three-dimensional velocity-depth model of the subsurface, using the widest possible variety of data available from conventional seismic processing and allowing for moderate structural complexity. The result is a fully implemented inversion methodology that has been applied successfully to a large number of diverse case studies. A model-based inversion technique is presented and shown to be significantly more accurate than the analytical methods of velocity determination that dominate industrial practice. The inversion itself is based around two stages of ray-tracing. The first takes picked interpretations in migrated-time and maps them into depth using a hypothetical interval velocity field; the second checks the validity of this field by simulating fully the kinematics of seismic acquisition and processing as accurately as possible. Inconsistencies between the actual and the modelled data can then be used to update the interval velocity field using a conventional linear scheme. In order to produce a velocity-depth model that ties the wells, the inversion must include anisotropy. Moreover, a strong correlation between anisotropy and lithology is found. Unfortunately, surface seismic and well-tie data are not usually sufficient to uniquely resolve all the anisotropy parameters; however, the degree of non-uniqueness can be measured quantitatively by a resolution matrix which demonstrates that the model parameter trade-offs are highly dependent on the model and the seismic acquisition. The model parameters are further constrained by introducing well seismic traveltimes into the inversion. These introduce a greater range of propagation angles and reduce the non- uniqueness

Construção de um modelo inicial em profundidade usando métodos robustos de análise de velocidade por migração em tempo

Orientadores: Joerg Dietrich Wilhelm Schleicher, Maria Amélia Novais SchleicherTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de GeociênciasResumo: A necessidade de investigar regiões formadas por estruturas geológicas complexas tem motivado o desenvolvimento de métodos de imageamento que atuem no domínio da profundidade. Exemplos notáveis são as técnicas de migração pré-empilhamento em profundidade (PSDM, do inglês "prestack depth migration") e a tomografia de onda completa (FWT, do inglês "full-waveform tomography"). No entanto, a aplicação desses métodos enfrenta ao menos dois desafios: eles requerem (1) um modelo de velocidade (inicial) preciso, e (2) elevado poder computacional. Por outro lado, a migração em tempo provou ser um processo robusto e muito rápido, tornando-se rotineiramente empregado para o imageamento sísmico. Além disso, a construção de modelos de velocidade em tempo é um processo bem compreendido. Portanto, é altamente desejável usar as técnicas de conversão tempo-profundidade para construir, a partir desses modelos de velocidade no domi?nio do tempo, modelos de velocidade iniciais para te?cnicas que operam em profundidade. Neste trabalho, investigamos a aplicabilidade de um fluxo de trabalho formado por alguns recém-desenvolvidos métodos (semi-) automáticos de análise de velocidade de migração em tempo (MVA, do inglês "migration velocity analysis"), capazes de gerar modelos de velocidade e imagens migradas no tempo sem precisar de informações a priori, seguido por uma técnica robusta de conversão tempo-profundidade. Discutimos as vantagens e limitações desse fluxo de trabalho e suas perspectivas para se tornar uma ferramenta plenamente automática, capaz de gerar modelos de velocidade sísmica para o uso subsequente em métodos de FWT. Nos nossos testes em diferentes versões dos dados Marmousi, o procedimento proposto produziu modelos de velocidade iniciais suficientemente precisos para uma FWT sob condições quase ideais. Começando no modelo de velocidade do domínio do tempo convertido para profundidade, a FWT convergiu para um modelo final com qualidade comparável a quando feito a partir de uma versão suavizada do modelo de velocidade verdadeiro. Isso indica que a correta informação sobre a velocidade de fundo pode ser extraída com sucesso pela MVA automática no domínio do tempo mesmo em meios onde a migração em tempo não pode fornecer imagens sísmicas satisfatórias. Como resultado, esta tese não só contribui para o desenvolvimento de um fluxo de trabalho para a construção de modelos de velocidade iniciais para a FWT, mas também apresenta várias aplicações inovadorasAbstract: The need to investigate regions with complex geology has encouraged the development of imaging methods that act in the depth domain. Notable examples are prestack depth migration (PSDM) and full-waveform tomography (FWT). However, the application of these techniques faces at least two challenges: they require (1) an accurate (initial) velocity model and (2) massive computation power. In contrast, time migration has proven to be a fast and robust process, making it routinely used for seismic imaging. Moreover, time-domain velocity-model building is a well-understood process. Therefore, it is highly desirable to use time-to-depth conversion to construct starting models for depth-imaging techniques from these time-domain velocity models. In this work, we investigate the applicability of a workflow consisting of some recent (semi-) automatic time migration-velocity-analysis (MVA) methods, which can generate a velocity model and a time-migrated image without a priori information, followed by a robust time-to-depth conversion technique. We discuss advantages and limitations of this workflow and its perspectives to become a fully automatic tool, capable of generating initial seismic depth velocity models for subsequent FWT methods. In our tests on different versions of the Marmousi data, the proposed procedure produced sufficiently accurate initial models for an FWT under nearly ideal conditions. Starting at the depth-converted time-domain model, FWT converged to a final model of comparable quality as when starting at a smoothed version of the true velocity model. This indicates that correct background velocity information can be successfully extracted from automatic time-domain MVA even in media where time-migration cannot provide satisfactory seismic images. In effect, this thesis not only contributes to the development of a workflow for the construction of initial velocity-models for FWT but also presents several innovative applications thereofDoutoradoReservatórios e GestãoDoutor em Ciências e Engenharia de Petróle

Model building and imaging with reflection data

The purpose of the first part of this dissertation was to develop a migration algorithm for converted waves, and a tomographic method for estimating an interval shear wave velocity model. The developed algorithm is based on the Kirchhoff formalism. The elastic Kirchhoff integral and its implementation were discussed and summarised in Chapter 2. The derived migration integral was generalised for all types of multicomponent data. For practical reasons, multicomponent data are decomposed into their corresponding components (z,x, and y components), and the migration is performed separately for each component. Normally it is assumed that the decomposed wave components are free from other wave types. The migration result of each component shows particular characteristics of the subsurface. For example, PS data give the shear wave characteristics of the subsurface...thesi

Seismic attributes in hydrocarbon reservoirs characterization

Mestrado em Engenharia GeológicaNo presente trabalho apresentam-se as vantagens da utilização de atributos sísmicos na interpretação de dados de sísmica de reflexão 3D e na identificação e caracterização de reservatórios de hidrocarbonetos. O trabalho prático necessário para a elaboração desta tese foi realizado durante um estágio de quatro meses na empresa de serviços para a indústria petrolífera, Schlumberger, em Paris, utilizando o software de interpretação sísmica e de modelação de reservatórios de hidrocarbonetos, Petrel 2008.1. Os atributos sísmicos podem ser considerados formas alternativas de visualizar os dados de sísmica de reflexão, que normalmente são representados em amplitude. A sua utilização facilita o processo de interpretação sísmica, uma vez que permite aumentar a razão sinal-ruído, detectar descontinuidades, reforçar a continuidade dos reflectores sísmicos e evidenciar indicadores directos de hidrocarbonetos nos dados sísmicos originais. Os atributos sísmicos podem ainda ser usados para treinar processos de auto-aprendizagem utilizados em redes neuronais na predição da distribuição de facies numa área em estudo. De uma forma geral, a utilização de atributos sísmicos facilita a correlação entre os dados provenientes do método sísmico, dados de poços e a geologia da área em estudo. Neste trabalho foi utilizado um bloco migrado de sísmica de reflexão 3D, com aproximadamente 6000 km2, adquirido no deep-offshore da costa Oeste Africana. Para além de um teste individual dos atributos sísmicos disponíveis no Petrel 2008.1, esta tese incluí uma avaliação preliminar do potencial em hidrocarbonetos de um sistema de canais amalgamados identificado na área em estudo. A sua identificação, interpretação e caracterização foi possível com o recurso a atributos sísmicos que evidenciam a presença de falhas, ou outras descontinuidades, e de atributos sísmicos sensíveis a pequenas variações na litologia e à presença de fluídos nos poros das formações litológicas. ABSTRACT: In this work the advantages related to the use of seismic attributes in the interpretation of 3D seismic data and in the characterization of hydrocarbon reservoirs are discussed. A four months internship at Schlumberger, in Paris, using the Petrel 2008.1 “seismic-to-simulation” software provided the necessary data to perform the work described in this thesis. Seismic attributes are different ways to look at the original seismic data, which normally is displayed in amplitudes. Using seismic attributes during the seismic interpretation process allow a significant improvement in the signal-to-noise ratio, the automatic detection of discontinuities, the enhancement of seismic reflectors continuity and the enhancement of direct hydrocarbon indicators. In the self-learning process for neural networks, seismic attributes can be used as training data to predict facies distribution in the study area. Generally, seismic attributes provide a better correlation between the data provided by the seismic reflection method, well log data and the geology of the study area. In this work, a 3D migrated seismic cube was used, with an approximate area of 6000km2, acquired in the deep-water of West Africa. Besides an individual test of each attribute available in Petrel 2008.1, this thesis also includes a preliminary evaluation of the oil and gas potential of a system of stacked channels identified within the study area. The identification, interpretation and characterization of this potential hydrocarbon reservoir was possible using seismic attributes to enhance faults and other discontinuities, and by using seismic attributes sensitive to subtle lithological variations and the presence of fluids in the pore spaces of the lithological formations

Practical solutions for seismic free-surface and internal multiple attenuation based on inversion

Multiple prediction through inversion (MPI) is an effective method for seismic multiple attenuation. The research in this thesis aims to make the MPI method more practical for both free-surface and internal multiple attenuation. For free-surface multiple attenuation, the MPI scheme requires the input data to be dense and regularly sampled, and with one shot at each receiver position. In order to meet these requirements, I use a multilevel B-spline method for seismic data reconstruction. This method can perform regularisation and interpolation on seismic data without any prior-knowledge of models. For free-surface multiple attenuation on marine data, MPI can generate superior results compared to SRME (surface-related multiple attenuation). However, MPI is more computationally expensive due to the large amount of matrix operations involved. The conventional implementation addresses this by approximating the multiple model prediction operator as a pentadiagonal or a tridiagonal matrix. Tackle this problem by solving the full prediction operator using a Graphic Processing Unit (GPU), this accelerates the processing and improve the multiple attenuation results, especially for far-offset traces. As extensions of SRME for internal multiple attenuation, both the CFP (common-focus-point) technique and correlation method have problems. The results can be improved using the MPI method with GPU acceleration. The correlation method is preferred as the initial step for MPI because it can be implemented as a fully data-driven pre-stack domain approach in either forward data space or inverse data space. In all cases, the MPI scheme generates internal multiple models with improved kinematic and dynamic accuracy

Wave-equation based seismic multiple attenuation

Reflection seismology is widely used to map the subsurface geological structure of the Earth. Seismic multiples can contaminate seismic data and are therefore due to be removed. For seismic multiple attenuation, wave-equation based methods are proved to be effective in most cases, which involve two aspects: multiple prediction and multiple subtraction. Targets of both aspects are to develop and apply a fully datadriven algorithm for multiple prediction, and a robust technique for multiple subtraction. Based on many schemes developed by others regarding to the targets, this thesis addresses and tackles the problems of wave-equation based seismic multiple attenuation by several approaches. First, the issue of multiple attenuation in land seismic data is discussed. Multiple Prediction through Inversion (MPTI) method is expanded to be applied in the poststack domain and in the CMP domain to handle the land data with low S/N ratio, irregular geometry and missing traces. A running smooth filter and an adaptive threshold K-NN (nearest neighbours) filter are proposed to help to employ MPTI on land data in the shot domain. Secondly, the result of multiple attenuation depends much upon the effectiveness of the adaptive subtraction. The expanded multi-channel matching (EMCM) filter is proved to be effective. In this thesis, several strategies are discussed to improve the result of EMCM. Among them, to model and subtract the multiples according to their orders is proved to be practical in enhancing the effect of EMCM, and a masking filter is adopted to preserve the energy of primaries. Moreover, an iterative application of EMCM is proposed to give the optimized result. Thirdly, with the limitation of current 3D seismic acquisition geometries, the sampling in the crossline direction is sparse. This seriously affects the application of the 3D multiple attenuation. To tackle the problem, a new approach which applies a trajectory stacking Radon transform along with the energy spectrum is proposed in this thesis. It can replace the time-consuming time-domain sparse inversion with similar effectiveness and much higher efficiency. Parallel computing is discussed in the thesis so as to enhance the efficiency of the strategies. The Message-Passing Interface (MPI) environment is implemented in most of the algorithms mentioned above and greatly improves the efficiency