The first main goal of this research is to develop comprehensive analytical and numerical models for the stress distribution around an inclined cased wellbore by considering all wellbore processes and to amend erroneous models of most previous work. The second main goal is to apply the developed models to explain near wellbore phenomena such as cement failure and sand production. To achieve these goals, this work checked the eligibility of using simple elastic approaches for the system by using a poroelastic undrained condition and a steady state condition for stresses induced by wellbore temperature variation. It utilized the generalized plane strain to compensate for the limitation of the plane strain which most previous work had used. In addition, this research developed comprehensive models to improve previous work by using superposing principles. For applying the developed models to cement failure, Mogi-Coulomb criterion for shear failure instead of Mohr-Coulomb and Drucker-Prager criteria was used to properly consider the intermediate stress. Additionally, ABAQUSr was utilized for numerical models with the "model change" option to simulate and combine all individual wellbore processes while MATLABr was used for analytical models. For predicting sand production, fully coupled poroelastic solutions for an inclined open wellbore were modified to obtain the stress distribution around a perforation tunnel after perforating. Then, modified Lade failure criterion was used to calculate the critical drawdown when sand production occurs, that is, when the perforation tunnel starts failure. This research obtained the following results. For developing models, the analytical models improved the previous research. However, the numerical results under a vertical tectonic stress showed discrepancies because of the difference between the generalized plane strain and numerical models. For cement failure, Young's modulus of cement, wellbore pressure and wellbore temperature variation could affect shear failure more significantly than the other factors. The numerical results showed closer to the failure envelopes than the analytical results. For predicting sand production, well completion affected sand production near wellbore and the critical drawdown converged to asymptotic values. In addition, perforating along the minimum horizontal stress direction was most preferable in a vertical cased wellbore under a normal stress regime. / text

[pt] O presente estudo descreve uma correlação entre o desempenho obtido por brocas de perfuração e o estado de tensões atuante na formação rochosa localizada imediatamente abaixo do fundo do poço. Os dados de desempenho de brocas de seis poços perfurados na costa marítima brasileira foram coletados e analisados. Tendo em vista reduzir o empirismo associado com este tipo de análise, é implementado um estudo que considera o perfil geomecânico do poço. O perfil geomecânico de uma dada formação rochosa é composto de suas propriedades mecânicas (módulo de Young, relação de Poisson, resistência à compressão simples, ângulo de atrito interno etc.), das pressões dos fluidos das formações e das tensões totais in situ. A dissertação mostra a sistemática utilizada para avaliar as tensões no fundo do poço através de um programa de elementos finitos 3D. Através destas tensões é possível definir um índice de plastificação à frente da broca de perfuração e o rendimento da mesma é avaliado levando este índice em conta. Alguns dos poços analisados foram perfurados em águas profundas, sendo que os resultados obtidos até o momento mostraram um grande potencial para a melhor compreensão de altos e baixos rendimentos com respeito à taxa de penetração da broca, de uma maneira racional. Baseados nesta análise novos estudos para avaliação de brocas poderão ser implementados indicando que reduções significativas de custo de perfuração poderão ser obtidas. / [en] The present dissertation describes a correlation between the bit performance and the state of stress acting upon the rock formation located immediately beneath the bottom of the wellbore. Bit performance data from 6 wells drilled offshore Brazil were collected and anlyzed. In order to reduce the empiricism associated with this type of data analysis, a study is being put forward that considers the geomechanical log along the drilled wellbore. The geomechanical log of a given rock formation is composed of its mechanical properties (Young's modulus, Poisson's Ratio, unconfined compressive strength, internal friction angle, etc.) as well as formation fluid pressure and in situ total stresses. The dissertation shows the metodology to evaluate the stresses at the bottom of the wellbore through a 3D finite element program. Trough these stresses it is possible to define an index of plastification ahead of the drill bit, and bit performance is rated taking this index into account. Some of the wells analyzed were drilled in deep water locations, and the initial results obtained herein, showed a great potential for better understanding for the good and bad performances, regarding the rate of penetration of the drill bit evaluation will be put forward with the great potential for drilling cost savings. / [es] El presente estudio describe la correlación entre el desempeño obtenido por brocas de perforación y las tensiones actuantes en la formación rocosa localizada debajo del fondo del pozo. Se colectaron y analizaron datos sobre el desempeño de brocas de seis pozos perforados en la costa marítima brasileira. Teniendo como objetivo reducir el empirismo asociado a este tipo de análisis, se implementa un estudio que considera el perfil geomecánico del pozo. El perfil geomecánico de una formación rocosa está compuesto de suas propriedades mecánicas (módulo de Young, relación de Pueson, resistencia a la compresión simple, etc.), de las presiones de los fluidos de las formaciones y de las tensiones totales in situ. La disertación muestra la sistemática utilizada para evaluar las tensiones en el fondo del pozo a través de un programa de elementos finitos 3D. A través de estas tensiones es posible definir un índice de plastificación al frente de la broca de perfuración y se evalúa su rendimiento llevando este índice en consideración. Algunos pozos analizados fueron perforados en aguas profundas, los resultados obtenidos hasta el momento mostraron un gran potencial para la mejor comprensión de altos y bajos rendimentos con respecto a la tasa de penetración de la broca, de una manera racional. Sobre este análisis nuevos estudios para evaluación de brocas pueden ser implementados indicando que pueden obtenerse reducciones significativas del costo de perforación.

Made available in DSpace on 2014-12-17T14:09:10Z (GMT). No. of bitstreams: 1 ClovisDF_TESE_partes_autorizadas.pdf: 2764652 bytes, checksum: e400922c312c00169022c2f987a6d8b7 (MD5) Previous issue date: 2010-08-13 / The development of oil wells drilling requires additional cares mainly if the drilling is in offshore ultra deep water with low overburden pressure gradients which cause low fracture gradients and, consequently, difficult the well drilling by the reduction of the operational window. To minimize, in the well planning phases, the difficulties faced by the drilling in those sceneries, indirect models are used to estimate fracture gradient that foresees approximate values for leakoff tests. These models generate curves of geopressures that allow detailed analysis of the pressure behavior for the whole well. Most of these models are based on the Terzaghi equation, just differentiating in the determination of the values of rock tension coefficient. This work proposes an alternative method for prediction of fracture pressure gradient based on a geometric correlation that relates the pressure gradients proportionally for a given depth and extrapolates it for the whole well depth, meaning that theses parameters vary in a fixed proportion. The model is based on the application of analytical proportion segments corresponding to the differential pressure related to the rock tension. The study shows that the proposed analytical proportion segments reaches values of fracture gradient with good agreement with those available for leakoff tests in the field area. The obtained results were compared with twelve different indirect models for fracture pressure gradient prediction based on the compacting effect. For this, a software was developed using Matlab language. The comparison was also made varying the water depth from zero (onshore wellbores) to 1500 meters. The leakoff tests are also used to compare the different methods including the one proposed in this work. The presented work gives good results for error analysis compared to other methods and, due to its simplicity, justify its possible application / O desenvolvimento da perfura??o de po?os de petr?leo requer cuidados adicionais principalmente se a perfura??o for mar?tima em l?mina d ?gua ultraprofunda, o que levam a baixos gradientes de sobrecarga, ocasionando baixos gradientes de fratura e, conseq?entemente, dificultando as opera??es de perfura??o pela redu??o da janela operacional. Para minimizar as dificuldades enfrentadas pela perfura??o nesses cen?rios, na fase de planejamento, s?o utilizados modelos indiretos para estimativa do gradiente de fratura, que podem prev? valores aproximados dos testes de absor??o. Esses modelos geram perfis de geopress?o que permitem a an?lise detalhada do comportamento das press?es em todo o intervalo do po?o. A maioria dos modelos tem como base a equa??o de Terzaghi, diferenciando apenas na determina??o dos valores do coeficiente de tens?o da matriz da rocha. Este trabalho prop?e uma forma alternativa diferente, para se estimar o gradiente de fratura, por meio de uma correla??o geom?trica que relaciona proporcionalmente os gradientes de press?o para cada profundidade em todo o intervalo do po?o. As grandezas envolvidas variam em uma mesma propor??o em todo intervalo do po?o. O modelo baseia-se na aplica??o da propor??o ?urea do segmento sobre o diferencial de press?o correspondente ? tens?o da matriz. O estudo mostra que a propor??o ?urea encontra valores de gradiente de fratura com grande aproxima??o dos valores de testes de absor??o dispon?veis da ?rea. Os resultados obtidos foram comparados com doze modelos indiretos distintos que estimam gradiente de fratura baseados no efeito da compacta??o. Para isto, um programa em linguagem Matlab foi desenvolvido. A compara??o tamb?m foi feita com a varia??o de l?minas d ?gua variando de zero (para po?os terrestres, por exemplo) a 1500 m. A medida da precis?o para avalia??o de cada m?todo toma como referencial os valores de testes de absor??o e ? feita atrav?s do erro relativo percentual. A precis?o mostrada nos valores apresentados na an?lise de erro e a forma bastante simples do modelo proposto mostram que ? justific?vel a sua aplica??o

Durante o processo de perfuração de poços de óleo e gás, em geral a passagem e oscilações da broca de perfuração provoca a ovalização das paredes do poço. O presente trabalho apresenta um estudo analítico e numérico do escoamento de fluido viscoplástico tipo Herschel-Bulkley através de três configurações de tubos de seções transversais elípticas: tubo elíptico, elíptico anular concêntrico e excêntrico. O objetivo desse estudo é analisar o efeito dos parâmetros geométricos do tubo, cinemáticos do escoamento e reológicos do fluido na perda de carga. A modelagem matemática foi realizada com base nas equações de balanço de massa e de quantidade de movimento e uma equação constitutiva para o tensor tensão do fluido. Para a solução analítica são utilizados os métodos de transformação de coordenadas e da folga variável modelando o escoamento como entre placas paralelas. Para a solução numérica é empregado o método de volumes finitos. As simulações numéricas são realizadas com o programa comercial PHOENICS-CFD. Para validar os resultados, são realizadas comparações com a literatura. Para cada geometria investigada foram obtidos os parâmetros de interesse na engenharia como: perfil de velocidade, vazão volumétrica, perfil das tensões e expressão para o fator de atrito. Os resultados para o duto anular circular concêntrico e excêntrico são corretamente reproduzidos quando a seção anular elíptica tende para a razão de aspecto unitária. / During the oil well drilling operations, the oscillations and the advancement of the drill makes the well takes an oval shape. This work presents an analytical and numerical study of the viscoplastic fluid flow of a Herschel-Bulkley fluid, through three types of elliptical cross sections ducts: elliptical, concentric and eccentric elliptical annulus. The objective is to analyze the effects of the pipe geometrical parameters, the kinematics of the flow and the fluid rheology over the pressure drop. The mathematical model was based on the mass and momentum balance equations and a constitutive equation expressing the stress tensor of the fluid. The analytical solutions employed were an analytical transformation of coordinates and other one based on in the slot flow model and the fluid flow was modeled as parallel plates in narrow annuli. For the numerical solution of the balance equations the finite volume method was used. The numerical simulations were carried out with PHOENICS-CFD. For validation of the results, comparisons with numerical and analytical results available in literature were done. Relevant engineering parameters were obtained, like velocity profiles, volumetric flow rate, shear stress profiles and an expression for the friction factor. The results for the concentric and eccentric circular annulus are adequately reproduced when the elliptical cross section tends towards unitary aspect ratio.

Durante o processo de perfuração de poços de óleo e gás, em geral a passagem e oscilações da broca de perfuração provoca a ovalização das paredes do poço. O presente trabalho apresenta um estudo analítico e numérico do escoamento de fluido viscoplástico tipo Herschel-Bulkley através de três configurações de tubos de seções transversais elípticas: tubo elíptico, elíptico anular concêntrico e excêntrico. O objetivo desse estudo é analisar o efeito dos parâmetros geométricos do tubo, cinemáticos do escoamento e reológicos do fluido na perda de carga. A modelagem matemática foi realizada com base nas equações de balanço de massa e de quantidade de movimento e uma equação constitutiva para o tensor tensão do fluido. Para a solução analítica são utilizados os métodos de transformação de coordenadas e da folga variável modelando o escoamento como entre placas paralelas. Para a solução numérica é empregado o método de volumes finitos. As simulações numéricas são realizadas com o programa comercial PHOENICS-CFD. Para validar os resultados, são realizadas comparações com a literatura. Para cada geometria investigada foram obtidos os parâmetros de interesse na engenharia como: perfil de velocidade, vazão volumétrica, perfil das tensões e expressão para o fator de atrito. Os resultados para o duto anular circular concêntrico e excêntrico são corretamente reproduzidos quando a seção anular elíptica tende para a razão de aspecto unitária. / During the oil well drilling operations, the oscillations and the advancement of the drill makes the well takes an oval shape. This work presents an analytical and numerical study of the viscoplastic fluid flow of a Herschel-Bulkley fluid, through three types of elliptical cross sections ducts: elliptical, concentric and eccentric elliptical annulus. The objective is to analyze the effects of the pipe geometrical parameters, the kinematics of the flow and the fluid rheology over the pressure drop. The mathematical model was based on the mass and momentum balance equations and a constitutive equation expressing the stress tensor of the fluid. The analytical solutions employed were an analytical transformation of coordinates and other one based on in the slot flow model and the fluid flow was modeled as parallel plates in narrow annuli. For the numerical solution of the balance equations the finite volume method was used. The numerical simulations were carried out with PHOENICS-CFD. For validation of the results, comparisons with numerical and analytical results available in literature were done. Relevant engineering parameters were obtained, like velocity profiles, volumetric flow rate, shear stress profiles and an expression for the friction factor. The results for the concentric and eccentric circular annulus are adequately reproduced when the elliptical cross section tends towards unitary aspect ratio.

In this work, five water produced samples from oil fields onshore (land) of the Sergipe State were characterized. The physico-chemical parameters such as pH, conductivity, turbidity, suspended solids, biochemical oxygen demand (BOD) and content of oil and grease (TOG) were determined. The concentrations of anions (Br-, Cl-, F-, NO3- and SO42-) and cations (Ca2 +, K +, Mg2+, Na +, and NH4+) were determined by ion chromatography (IC). The total arsenic was determined by hydride generation atomic fluorescence spectrometry (HG AFS). For trace metals determination (Ba, Cd, Cr, Cu, Fe, Li, Mn, Ni, Pb, V and Zn) was used inductively coupled plasma mass spectrometry (ICP-MS). The limit of quantification (LOQ) ranged between 0.07 ìg L-1 (Cd e V) and 22 ìg L-1 (Fe). The precision was expressed as relative standard deviation (RSD) ranged between 0.03% (Na+) and 7.39% (F-). The values of recoveries obtained were between 85 ± 3% (Zn) and 112 ± 1% (Li). The results were compared to the values established by Resolution 430/2011 of the National Council for the Environment (CONAMA). To evaluate the data, the principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used. The concentrations of BOD, TOG, Ba, Mn and Fe were higher than those allowed by law, for some samples. The pH and concentration of As, Pb, Cr, Cu and Ni, for all samples, were consistent with established values. The conductivity, turbidity, suspended solids, concentration of anions, cations, Li and V are not required by law. The concentrations of Cd and Zn were below the LOQ of the method. In general, all the samples have very similar profiles with relatively close found values for all parameters. It was found that the samples have characteristics and inorganic constituents, which may cause damage to environment or generate drawbacks when used for reinjection. Therefore, the monitoring and characterization the produced water from onshore oil fields are very important for proper treatment of this effluent. / Neste trabalho, foram caracterizadas cinco amostras de agua produzida, provenientes de campos petroliferos onshore (terrestres) do Estado de Sergipe. Foram determinados os parametros fisico-quimicos, como pH, condutividade, turbidez, solidos suspensos, demanda bioquimica de oxigenio (DBO) e teor de oleos e graxas (TOG). Os anions (Br- , Cl-, F-, NO3- e SO42-) e cations (Ca2+, K+, Mg2+, Na+ e NH4+) foram determinados por cromatografia de ions (IC). O arsenio total foi determinado por espectrometria de fluorescencia atomica com geracao de hidreto (HG AFS). Para determinacao dos metais traco (Ba, Cd, Cr, Cu, Fe, Li, Mn, Ni, Pb, V e Zn) foi utilizada a espectrometria de massa com plasma indutivamente acoplado (ICP-MS). Os valores de limite de quantificacao (LQ) variaram entre 0,07 Êg.L-1 (Cd e V) e 22 Êg.L-1 (Fe). A precisao foi expressa como desvio padrao relativo (RSD), variando entre 0,03% (Na+) e 7,39% (F-). Os valores de recuperacoes ficaram entre 85 } 3 % (Zn) e 112 } 1% (Li). Os resultados obtidos foram comparados aos valores estabelecidos pela Resolucao 430/2011 do Conselho Nacional de Meio Ambiente (CONAMA). Para avaliar os dados, utilizou-se a analise de componente principal (PCA) e analise de agrupamento hierarquico (HCA). Os valores das concentracoes de DBO, TOG, Ba, Mn e Fe foram maiores do que os permitidos pela legislacao, para algumas amostras. Os valores de pH e constituintes inorganicos (As, Pb, Cr, Cu e Ni) para todas as amostras foram concordantes com os valores estabelecidos. A condutividade, turbidez, solidos suspensos, concentracao de anions, cations, Li e V ainda nao sao previstos por lei. Os valores de concentracao de Cd e Zn ficaram abaixo do LQ do metodo. No geral, todas as amostras possuem perfis bem semelhantes, com valores encontrados relativamente proximos para todos os parametros. Foi constatado que as amostras possuem caracteristicas e constituintes inorganicos, que podem causar danos ao meio ambiente ou gerar empecilhos quando utilizadas para fins de reinjecao. Portanto, o monitoramento e caracterizacao das aguas produzidas provenientes de campos petroliferos onshore sao de grande importancia para o tratamento adequado deste efluente.

Orientador: Paulo Roberto Ribeiro / Dissertação (mestrado) - Universidade Estadual de Campinas. Faculdade de Engenharia Mecanica e Instituto de Geociencias / Made available in DSpace on 2018-08-12T18:02:11Z (GMT). No. of bitstreams: 1 PaulaJunior_RubensRibeirode_M.pdf: 2205711 bytes, checksum: 8d99ae4553a735e11f7c7662c3878d30 (MD5) Previous issue date: 2008 / Resumo: O trabalho apresenta uma revisão da literatura sobre poços HPHT, abordando o desafio na construção dos mesmos, com ênfase no aspecto de segurança de poço. Do ponto de vista de desenvolvimento, o trabalho envolveu a implementação de um modelo de controle de poços com fluidos de perfuração não aquosos em software existente (Unikick), que incorpora correlações empíricas derivadas de resultados experimentais com n-parafina e diesel. A importância dessa implementação deve-se ao fato de que a previsão do comportamento das pressões, vazões e volumes desenvolvidos em um poço durante a detecção e circulação de um kick de gás, é muito útil para o engenheiro de perfuração que poderá tomar decisões sobre a maneira mais segura de lidar com estas situações. Alguns estudos de casos foram realizados através de comparação dos resultados obtidos pelo Unikick e outros simuladores disponíveis e análise de sensibilidade de parâmetros. Nessa análise, foram simuladas circulações de kicks em terra e marítimos em várias lâminas d'água, com trajetórias verticais e horizontais e observados os comportamentos de parâmetros importantes durante o controle do poço, como a pressão no choke, pit gain e vazão de gás na superfície. / Abstract: The first part of the work provides a review of the literature on HPHT wells, addressing the challenge in the construction of these wells, emphasizing the safety aspects. From the point of view of development, the work involved an implementation of a well control model for nonaqueous drilling fluids using existing software (Unikick), that incorporates empirical correlations derived from experimental results with n-paraffin and diesel. The importance of this implementation is due to the fact that the estimation of the behavior of pressures, flow rates and volumes developed inside a well during gas kick detection and circulation out of the well is very useful for the drilling engineer to take decisions about the safest way to handle these situations. Some case studies were performed through the comparison of simulated results from Unikick and other simulators available and a sensitivity analysis. In this analysis, some kick circulations were simulated in onshore and offshore wells with various water depths, vertical and horizontal trajectories, when important parameters of well control were observed, such as choke pressure pit gain and gas flow rate at surface. / Mestrado / Explotação / Mestre em Engenharia Mecânica

Este trabalho apresenta uma análise paramétrica da reposta dinâmica de colunas de perfuração de poços de petróleo com controle proporcional-integral de velocidade não colocalizado. A operação de perfuração de poços de petróleo e gás em águas profundas consiste na abertura de poços em solo rochoso através de uma broca cuja rotação é controlada por uma mesa rotativa na superfície. O torque imposto pela mesa é transmitido à broca por meio de uma coluna de perfuração. Particularmente no caso de perfuração em águas profundas, as colunas de perfuração podem ser muito extensas e, portanto, bastante flexíveis. As vibrações ocasionadas pela grande flexibilidade das colunas de perfuração são as principais responsáveis por falhas no processo de perfuração. Em particular, o fenômeno não-linear conhecido como stick-slip e relacionado às vibrações torcionais da coluna de perfuração, faz com que um sistema de controle projetado para manter a velocidade da mesa constante dê origem a grandes oscilações na velocidade da broca. Na prática, este fenômeno é amplificado pela inerente não-linearidade do contato entre broca e formação rochosa e pela forte não colocalização entre mesa rotativa e broca. Este trabalho tem por principal objetivo realizar uma análise paramétrica da dinâmica do processo de perfuração, usando um modelo de dois graus de liberdade para representar o conjunto mesa rotativa, coluna de perfuração e broca, para identificar condições nas quais uma lei de controle simples do tipo linear proporcional-integral pode fornecer um desempenho de perfuração estável e satisfatório. / This paper presents a parametric analysis of the dynamics of oilwell drillstrings with non-collocated proportional-integral velocity control. The drilling operation for oil and gas in deep waters consists of opening wells in rocky ground formation by a drill, whose angular speed is controlled by a rotary table at the surface. The torque applied by the table is transmitted to the drill-bit through the drillstring. Particularly in the deepwater drilling case, the drillstring can be very long and therefore very flexible. The vibrations caused by the great flexibility of drilling columns are mainly responsible for the failures in the drilling process. In particular, the nonlinear phenomenon known as stick-slip and related to the torsional vibration of the drillstring, makes that a control system designed to maintain a constant angular velocity at the table yield large variations at the drill-bit angular velocity. In practice, this phenomenon is amplified by the inherent nonlinearity of the contact between drill bit and rock formation and by the strong non-colocalization between rotary table and drill-bit. The main objective of this work is to perform a parametric analysis of the dynamics of the drilling process, using a two degrees of freedom model in order to represent the rotary table assembly, the drilling column and drill-bit, to identify conditions in which a simple control law, such as a linear proportional-integral velocity control, can provide a stable and satisfactory drilling performance.

This study is part of an NRF sponsored research project entitled “Neotectonics and its applications for the exploration of groundwater in the fractured Karoo aquifers in the Eastern Cape” under the NRF Niche area of Water Resources Management and Sustainable Development in the Eastern Cape Province. The identification of relatively highly productive wells in the Karoo fractured aquifers is extremely difficult. This study aims to identify neotectonic zones and lower stress fields, and apply the results to groundwater exploration in the Eastern Cape Province. The methodologies adopted in this study include: a comprehensive literature review, extensive field mapping and investigation such as road cuts, sampling for laboratory studies, examination of seismic data, study of hot and ordinary springs, and interpretation of aerial photography and satellite images. Three main neotectonic belts were identified in the Eastern Cape (southern neotectonic belt, northern neotectonic belt and eastern neotectonic belt) based on literature review and field interpretations. The southern neotectonic belt (from the Cape Fold Belt to the lower Beaufort Group boundary) is characterized by the reactivation of the Coega-Bavianskloof and Sauer faults, the presence of a hot spring near Fort Beaufort, the slickenlines and discrete slickenlines and specifically the seismic events that were recorded in the Eastern Cape from 1850 to 2007. In this southern neotectonic belt the remote sensing has also revealed the presence of the Fort Beaufort fracture, the quartz veins seen in some dolerites and the different vegetation types along it may indicate that this fracture is possibly a fault; moreover the Quaternary sediments and weathered dolerites indicate that the Fort iii Beaufort fracture is characterized by groundwater circulation and accordingly is a good target for groundwater exploration, this fracture is a post-Karoo structure and possibly a neotectonic feature. In addition, the kaolin deposit, chiefly developed in the Dwyka tillite near Grahamstown is clearly controlled by neotectonic fracture zones. The northern neotectonic belt near the country of Lesotho is marked by the presence of the Senqu seismotectonic regime and hot springs. The Quaternary Amatole-Swaziland (formerly Ciskei-Swaziland) axis of uplift makes the eastern part of the province the third neotectonic zone, the asymmetric meanders of the Mbashe river in the vicinity of Qunu near Mthatha derived possibly from this Quaternary uplift; this asymmetric feature of meanders implies that the river has tried to maintain stability of its valley where tilting occurred. Within these neotectonic belts the central part of the Eastern Cape may be considered a static and inactive belt. A northwesterly trend for the maximum principal compresssional stress predominates in the Eastern Cape and is correlated with the present major structural control of the province. The current stress regime determination was derived from faults, joints and quartz veins only on kaolin deposits. Systematic joints reflect regional tectonic stress trajectories at the time of fracturing. Discharge rates of groundwater from boreholes as provided by the Department of Water and Forestry were used to confirm and predict water exploration targets. The region of Tabankulu (near Kwazulu Natal) in the northern neotectonic belt has remarkable discharge rates of groundwater (11.1 l/s, 4.65 l/s, 6.49 l/s, 42 l/s). The region of Mthatha, nearly surrounding the Amatole-Swaziland axis (former Ciskei-Swaziland iv axis) of uplift which might have generated some new faults, has a number of springs. These two regions should serve as case studies for future research. Apart from these two regions, two others regions can be considered as case studies for future groundwater exploration targets: the Bath Farm hot spring near the Fort Beaufort neotectonic fault and the vicinity of what is known as the Fort Beaufort fracture near Teba and Cimezile villages 20km north west of Fort Beaufort. It is concluded that the study of neotectonics and stress fields may be a useful tool for groundwater exploration in the Karoo fractured aquifers in the Eastern Cape, and in similar regions elsewhere in South Africa and in Africa.

A exploração offshore tem crescido muito nos últimos anos e grandes estruturas e equipamentos têm sido projetados e construídos para remover o óleo que se encontra abaixo da superfície do mar. Para plataformas offshore fixas tipo jaqueta é necessário analisar os problemas decorrentes da exposição dessas instalações ao ambiente hostil do oceano. Estas perturbações induzem vibrações excessivas nas estruturas, afetando o conforto e a estabilidade da instalação, e para combater essas vibrações uma ferramenta matemática foi utilizada para monitorar o estado da integridade da estrutura, a Transformada de Hilbert-Huang (HHT). O HHT foi utilizada com sucesso para a identificação de parâmetros modais, como frequência fundamental e fator de amortecimento da plataforma. Finalmente, uma técnica de controle de vibração ativa baseada no Controle Linear Quadrático (LQ) é implementada com o objetivo de reduzir os efeitos de perturbações oscilatórias indesejáveis causados por ondas e correntes marinhas. / The offshore exploration has grown tremendously in recent years, and large structures and equipment has been designed and built to remove the oil that lies beneath the sea surface. For fixed jacket type offshore platforms is necessary to consider the problems arising from exposure of these facilities to the hostile ocean environment. These perturbations induce excessive vibrations in the structures affecting the comfort and stability of the facility, and for to combat these vibrations a mathematical tool was used to monitor the integrity health of the structure, namely the Hilbert-Huang Transform (HHT). The HHT was used for the successfully identification of modal parameters, as fundamental frequency and damping factor of the platform. Finally, an active vibration control technique based on the Control Linear Quadratic (LQ) is implemented aiming to reduce the effects of undesirable oscillatory perturbations caused by waves and marine current.