The origin of the Silverpit structure, UK North Sea has been contested since its discovery on seismic data in 2002. The Silverpit structure consists of a 3 - 4km central zone of deformation, which includes a conical uplift. This is surrounded by a series of ring faults up to a maximum diameter of 20km. Meteorite impact, evaporite withdrawal, pull-apart basin tectonics and halokinesis tectonics have all been suggested as possible origins. This thesis uses a multi-discipline approach to test these hypotheses and determine with certainty the origin of the Silverpit structure. Seismic interpretation of the Silverpit structure has highlighted that deformation in the central deformation zone and beneath the structure is comparable with other meteorite craters. However, the ring faults are comparable with other structures formed by regional evaporite dissolution and movement. Seismic interpretation on a regional, 3500km2 scale proved that the structure is unique and that salt movement was taking place at the same time as the Silverpit structure was created. Unusual diagenesis in the chalk beneath the Silverpit structure was identified as a result of the presence of both unusual geophysical and geochemical signatures. An anomalous sonic log response is attributed to a significantly decreased porosity at the base of the chalk unit. Anomalously negative stable oxygen isotopes were also found in the chalk beneath the structure. Unusually elevated heat flow is the likely cause of these irregularities. The evidence presented in this thesis leads to the conclusion that the origin of the Silverpit structure is in fact two-phase. Meteorite impact has lead to the formation of the central zone of deformation and conical uplift. It has also influenced the diagenesis of the chalk beneath the crater and created a more brittle chalk unit. Regional salt withdrawal is responsible for the formation of the ring faults, which have only formed in the meteorite impact induced brittle chalk. In simple terms, a meteorite impact formed the 3km crater and then salt withdrawal produced the circular rings during several million years after the impact.

The Gulf of Mexico (GOM) represents a challenge for exploration and production. Most of the sediments coming from North America has bypassed the shelf margin into Deep Water. In an Attempt to attack this challenge this thesis pretends to break the GOM's false bottom, mainly comprised by diverse salt structures and growth fault families. In this attempt, geological and geophysical data are integrated to find clues to potential hydrocarbons indicator (PHI) that could be of Reservoir Quality (RQ). 3D Pre stack depth migrated data comprised of Mississippi Canyon blocks, were interpreted: Top and base of salt, leading to the identification of a PHI represented by a consistent Amplitude Anomaly (AA) below and towards a salt structure. This AA may be of RQ and feasibility evaluation for further decisions may be taken. Following the structural sequences that Govern central GOM during Oligocene through out Miocene was important to support the results.

The goal of oil and gas exploration using seismic methods is to accurately locate geological structures that could host such reserves. As the search for these resources tends towards more complex regions, it is necessary to develop methods to extract as much information as possible from the seismic data acquired. Prestack depth imaging is a seismic processing technique that has the capability to produce a realistic depth image of geological structures in complex situations. However, improvements to this technique are required to increase the accuracy of the final depth image and ensure that the targets are accurately located. Although prestack depth imaging possesses the ability to produce a depth image of the Earth, it does have its disadvantages. Three problematic areas in depth imaging are: the computer run times (and hence costs) are excessively high; the success of depth migration is highly dependent upon the accuracy of the interval velocity model; and seismic multiples often obscure the primary reflection events representative of the subsurface geology. Velocity model building accounts for most of the effort in prestack depth imaging and is also responsible for the likelihood of success. However, the more effort that is expended on this process, the greater the cost of producing the required depth section. In addition, multiples remain a problem in complex depth imaging since many attenuation techniques are based assumptions that may only be approximately correct and in addition require a priori information. The Kirchhoff method is considered to be the workhorse in industry for prestack depth imaging. It is a simple and flexible technique to implement, and usually produces acceptable images at a small fraction of the cost of the other depth migration methods. / However, it is highly dependent on a method for calculating the traveltimes that are required for mapping data from the prestack domain to the output depth section. In addition, it is highly dependent on the accuracy of the interval velocity model. Multiples can also be problematic in complex geological scenarios. To improve the quality of the depth section obtained from Kirchhoff depth imaging, these three issues are considered in this thesis. This thesis took on the challenge of developing new techniques for (a) improving the accuracy and efficiency of traveltimes calculated for use in Kirchhoff prestack depth imaging, (b) building the interval velocity model, and (c) multiple attenuation in complex geological areas. Three new techniques were developed and tested using a variety of numerical models. A new traveltime computation method for simulating seismic multiple reflections was tested and compared with a Promax© finite-difference traveltime solver. The same method was also used to improve the computational efficiency whilst retaining traveltime accuracy. This was demonstrated by application to the well-known Marmousi velocity model and a velocity model obtained from analysis of data from the North West Shelf of Western Australia. / A new interval velocity model building technique that utilises the information contained in multiple events was also implemented and tested successfully using a variety of numerical models. Finally, a new processing sequence for multiple attenuation in the prestack depth domain was designed and tested with promising results being observed. Improved accuracy in the depth image can be obtained by combining the three techniques I have developed. These techniques enable this to be achieved by firstly improving traveltime accuracy and computation efficiency. These benefits are then combined with a more accurate interval velocity model and data with a minimal problematic multiple content to produce an accurate depth image. These new techniques for Kirchhoff depth imaging are capable of producing a depth section with improved accuracy, and with increased efficiency, that will aid in the process of seismic interpretation.

Climate change during the last 2.5 million years is characterised by glacial-interglacial cycles of fluctuating sea level and temperature increasing in magnitude and duration towards the present day. The central North Sea preserves these glacial-interglacial cycles in an expanded sedimentary sequence creating a high resolution palaeo-climatic record. Basin-wide, low-resolution 3D seismic data, covering more than 80,000 km2 of the central North Sea, is combined with high-resolution, broadband 3D seismic, regional 2D seismic and local ultra-high resolution seismic from the Dogger Bank windfarm development zone in order to investigate in full the sedimentary sequence. The evolution of the basin is analysed along with the preserved geomorphological landforms in order to build a framework for the development of the North Sea and its changing palaeo-environments from the inception of the Quaternary (2.58 Ma) until the extensive glacial unconformity formed during the Elsterian (0.48 Ma).At the onset of the Quaternary the structure of the North Sea was that of an elongate marine basin, rapidly infilled from the south by continued progradation of the large clinoformal deposits of the southern North Sea deltaic system. The basin rapidly decreased in extent and depth however it was not until around 1.1 Ma that the broad, shallow shelf of the present day was fully established. A revision of the current seismic stratigraphy is proposed, identifying four new Members within the Aberdeen Ground Formation taking into account the development of the basin through time. Powerful downslope gravity currents dominated the basin during much of the early Quaternary, although a well-established, anti-clockwise tidal gyre acted to gently modify the gravity currents. Iceberg scouring was nearly continual from the onset of the Quaternary until grounded ice sheets began to penetrate into the basin from 1.7 Ma, more than half a million years before any previous estimates. Effects of confluence of the British and Fennoscandian ice sheets are observed from 1.3 Ma. The tunnel valleys of the Dogger Bank represent a continuation of the North Sea tunnel valley network, interacting with both older glaciotectonic thrusting and younger glaciotectonic folded deformation.

>Magister Scientiae - MSc / The evaluation of petroleum reservoirs has shifted from single approach to an integrated approach. The integration, analysis and understanding of all available data from the well bore and creating property models is an exceptional way to characterize a reservoir. Formulating, implementing, and demonstrating the applicability of the joint inversion of seismic and well-bore related observations, and the use of information about the relationship between porosity and permeability as the key parameters for identifying the rock types and reservoir characterization is a vital approach in this study. Correlating well and seismic data, potential reservoirs can be delineated and important horizons (markers) can be pointed out to better characterize the reservoir. This thesis aims to evaluate the potential petroleum reservoirs of the Wells K-A1, K-A2, K-A3 and K-H1 of the Shungu Shungu field in the Orange Basin through the integration and comparison of results from core analysis, wireline logs and seismic and attempt to produce a good reservoir model and by additionally utilizing Petrophysics and seismic and trying to better understand why the area has dry wells. Different rock types that comprise reservoir and non reservoirs are identified in the study and five Facie types are distinguished. Tight, fine grained sandstones with low porosity values ranging from 3% - 6% where dominant in the targeted sandstone layers. Porosity values ranging from 11% - 18% where identified in the massive sandstone lithologies which where hosted by Well’s K-A2 and K-A3. Low permeability values reaching 0.1mD exist throughout the study area. Areas with high porosity also host high water saturation values ranging from 70 – 84%. An improvement in the porosity values at deeper zones (3700m -3725m) and is apparent. Poroperm plots exhibit quartz cemented sandstones and density with neutron plot suggest that the sandstones in the area contain quarts and dolomite mineralization.Well K-A3, consist of a cluster by quartzitic sandstone, meaning there is a large amount of sandstone present. There are apparent high porosity values around the sandstone. What is apparent from this plot is that there are many clusters that are scattered outside the chart. This could suggest some gas expulsions within this Well. Sandstones within the 14B2t1 to 14At1 interval are less developed in the vicinity covered by well K-A2 than at the K-A1 well location. The main targeted sandstones belong to the lower cretaceous and lie just below 13At1. The four wells drilled in this area are dry wells. The areas/blocks surrounding this area have shown to possess encouraging gas shows and a comparative study could reveal better answers. At deeper zones of the well at an interval of 5350m -5750m, there are more developed sandstones with good porosity values. The volume of shale is low and so is the water saturation. The main target sandstones in the study area are the Lower Cretaceous sandstones which are at an interval 13At1. These sandstones are not well developed but from the property model of the target surface it can be seen that the porosity values are much more improved than the average values applied on all the zones on the 3D grid.

No description available.

The two end-member concept of mantle plume-driven versus far field stress-driven continental rifting anticipates high volumes of magma emplaced close to the rift-initiating plume, whereas relatively low magmatic volumes are predicted at large distances from the plume where the rifting is thought to be driven by far field stresses. We test this concept at the Guinea Plateau, which represents the last area of separation between Africa and South America, by investigating for rift-related volumes of magmatism using borehole, 3D seismic, and gravity data to run structural 3D inversions in two different data areas. Despite our interpretation of igneous rocks spanning large areas of continental shelf covered by the available seismic surveys, the calculated volumes in the Guinea Plateau barely match the magmatic volumes of other magma-poor margins and thus endorse the aforementioned concept. While the volcanic units on the shelf seem to be characterized more dominantly by horizontally deposited extrusive volcanic flows distributed over larger areas, numerous paleo-seamounts pierce complexly deformed pre and syn-rift sedimentary units on the slope. As non-uniqueness is an omnipresent issue when using potential field data to model geologic features, our method faced some challenges in the areas exhibiting complicated geology. In this situation less rigid constraints were applied in the modeling process. The misfit issues were successfully addressed by filtering the frequency content of the gravity data according to the depth of the investigated geology. In this work, we classify and compare our volume estimates for rift-related magmatism between the Guinea Fracture Zone (FZ) and the Saint Paul's FZ while presenting the refinements applied to our modeling technique.

High rates of Neogene sediment influx to the offshore Canterbury Basin resulted in preservation of a high-resolution record of seismically resolvable sequences (~0.1-0.54 my periods). Subsequent sequence development was strongly influenced by submarine currents. This study focuses on correlating seismically interpreted sequence boundaries and sediment drifts architectures beneath the modern shelf and slope with sediment facies observed in cores from shelf Site U1351 and slope Site U1352 drilled by Integrated Ocean Drilling Program (IODP) Expedition 317. A traveltime-depth conversion was created using sonic and density logs and is compared with two previous traveltime-depth conversions for the sites. Eleven large elongate drifts were interpreted prior to drilling. Two new small-scale plastered slope drifts in the vicinity of the IODP sites, together with sediment waves drilled at Site U1352, have been interpreted as part of this study. Lithologic discontinuity surfaces and transitions together with associated sediment packages form the basis of identifying sequences and sequence boundaries in the cores. Contacts and facies were characterized using shipboard core descriptions, emphasizing grain-size contrasts and the natures of the lower and upper contacts of sediment packages. Lithologic surfaces in cores from sites U1351- (surfaces S1-S8) and U1352- (surfaces S1-S6) correlate with early Pleistocene to recent seismic sequence boundaries U12-U19 and U14-U19, respectively. The limited depths achieved by downhole logging, in particular sonic and density logs, together with poor recovery in the deeper section did not allow correlation of older lithologic surfaces. Slope Site U1352 experienced a complex interplay of along-strike and downslope depositional processes and cores provide information about the principal facies forming sediment waves. The general facies are fine-grained mud rich sediment interbedded decimeter-centimeter thick sand and sandy mud. Core evidence for current activity is reinforced at larger scale by seismic interpretations of sediment waves and drifts. / text

This study utilises seismic data to improve understanding of the subsurface fluid flow behaviour in the Taranaki and Great South Basins offshore New Zealand. The aim of this study is to characterise fluid flow features and to investigate their genesis, fluid origins and implications for subsurface fluid plumbing system by integrating seismic interpretation and 3D petroleum systems modelling techniques. After an early phase studying Pliocene pockmarks in the Taranaki Basin, this study has been focused on the subsurface fluid plumbing system and on the fluid expulsion history in the Great South Basin. The Taranaki Basin lies on the west coast and offshore of the North Island, New Zealand. The seismic interpretation revealed that paleo-pockmark formation in the study area relates to fluid escape due to a rapid sediment loading environment in a distal fan setting. Seismic analysis rules out any links between the paleo-pockmarks and faulting. The relationship between paleo-pockmark occurrence and fan depositional thickness variations suggests that pore-water expulsion during overburden progradation is the most likely cause of the paleo-pockmarks. The rapid sediment loading generated overpressure which was greatest on the proximal fan due to a lateral gradient in overburden pressure. Fluids were consequently forced towards the fan distal parts where, eventually, the pore pressure exceeded the fracture gradient of the seal. The Great South Basin lies off the southern coast of the South Island of New Zealand and is located beneath the modern shelf area. Evidence for past and present subsurface fluid flow in this basin is manifested by the presence of numerous paleo-pockmarks, seabed pockmarks, polygonal fault systems, bright spots and bottom simulating reflections (BSR), all of which help constrain aspects of the overburden plumbing system and may provide clues to deeper hydrocarbon prospectivity in this frontier region. The various types of fluid flow features observed in this study are interpreted to be caused by different fluid origins and mechanisms based on evidences from seismic interpretation in the study area. The possible fluid origins which contribute to fluid flow features in the Great South Basin are compactional pore water as well as biogenic and thermogenic hydrocarbons. Using 3D seismic attribute analysis it was possible to highlight the occurrence of these features, particularly polygonal faults and pockmarks, which tend to be hosted within fine-grained sequences. Paleo- and present-day fluid flow features were investigated using 3D basin and petroleum systems modelling with varying heat flow scenarios. The models predict that thermogenic gas is currently being generated in mid-Cretaceous sedimentary sequences and possibly migrates along tectonic faults and polygonal faults feeding present-day pockmarks at the seabed. The models suggest that biogenic gas was the main fluid source for the Middle Eocene paleo-pockmarks and compactional pore fluid may be the main fluid contributor to the Late Eocene paleo-pockmarks. Different heat flow scenarios show that only mid-Cretaceous source rocks have reached thermal maturity in the basin, whilst Late Cretaceous and Paleocene source rocks would be largely immature. The observations and interpretations provided here contribute to the ongoing discussion on basin de-watering and de-gassing and the fluid contributors involved in pockmark formation and the use of pockmarks as a potential indicator of hydrocarbon expulsion. It is clear from this study that seismically-defined fluid flow features should be integrated into petroleum systems modelling of frontier and mature exploration areas in order to improve our understanding on fluid phases, their migration routes, timings and eventual expulsion history.

O Gráben de Barra de São João, situado na região de águas rasas da Bacia de Campos, é parte integrante do Sistema de Riftes do Cenozóico, localizado na região sudeste do Brasil. Este sistema foi formado em um evento que resultou na reativação das principais zonas de cisalhamento do Pré-Cambriano do sudeste do Brasil no Paleoceno. Neste trabalho proponho um novo arcabouço estrutural para o Gráben de Barra de São João baseado na interpretação de dados gravimétricos. Dados magnéticos aéreos, dados gravimétricos, uma linha sísmica 2D e um perfil de densidades de um poço foram utilizados como vínculos na interpretação. Para a estimativa do topo do embasamento foi necessário separar o efeito das fontes profundas no dado gravimétrico (anomalia residual). Com isso, foi realizada uma modelagem 2D direta baseada na interpretação sísmica para estimar as densidades das entidades geológicas da área em questão. Após esta modelagem, foi realizada uma inversão estrutural 3D do dado gravimétrico residual a fim de recuperar a profundidade do topo do embasamento. Este fluxograma de interpretação permitiu a identificação de um complexo arcabouço estrutural com três sistemas de falhas bem definido: Falhas normais de orientação NE-SW, e um sistema de falhas transcorrentes NW-SE e E-W. Estas orientações dividem o gráben em diversos altos e baixos internos. O dado magnético aéreo corrobora esta interpretação. A existência de rochas ultra-densas e fortemente magnéticas no embasamento foram interpretadas como um ofiolito que foi provavelmente intrudido (por obducção) na época do fechamento de um oceano no Proterozóico. / Barra de São João Graben, shallow water Campos Basin, is part of the Tertiary rift system that runs parallel to the Brazilian continental margin. This system was formed in an event that caused the reactivation of the main Precambrian shear zones of southeastern Brazil in the Paleocene. I propose a new the structural framework of Barra São João Graben based on gravity data interpretation. Magnetic data an available 2D seismic line and a density well-log of a nearby well were used as constraints to our interpretation. To estimate the top of the basement structure we separated the gravity effects of deep-sources from the shallow basement (residual anomaly). Then, we performed a 2D modeling exercise, where we keptfixed the basement topography and the density of the sediments, to estimate the density of the basement rocks. Next, we inverted the residual anomaly to recover the depth to the top of the basement. This interpretation strategy allowed the identification of a complex structural framework with three main fault systems: NE-SW normal faults system, and a NW-SE and E-W transfer fault systems. These trends divide the graben into several internal highs and lows. The magnetic anomalies corroborate our interpretation. The existence of ultra-dense and strongly magnetized elongated bodies in the basementwere interpreted as ophiolite bodies that probably intruded by the time of the shutdown of the Proterozoic ocean.