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- Volume 14, Issue 3, 2008
Petroleum Geoscience - Volume 14, Issue 3, 2008
Volume 14, Issue 3, 2008
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An integrated approach to understanding the petroleum system of a frontier deep-water area, offshore Japan
More LessThe Naoetsu Basin is one of several oil- and gas-producing provinces in Japan where thick Neogene strata are deposited, and oil and gas are produced from both onshore and offshore shelf areas. It is believed that the Naoetsu Basin extends into deep-water areas, but exploration activities were limited until 2000, except for regional 2D seismic surveys. After acquisition of a 3D seismic survey in 2001, the first two wells were drilled in 2004 in the deep-water area of the Naoetsu Basin. One well encountered an oil zone.
Multi-dimensional basin modelling was conducted to understand the petroleum system in the deep-water area of the Naoetsu Basin before and after the wells were drilled. The accuracy of basin modelling depends on the accuracy of the input data as well as the calibration process. However, even after the drilling campaign, only two wells were available in the deep-water area of the Naoetsu Basin. Therefore, the integration of various kinds of data, information and different techniques, such as 3D seismic, sedimentological and geochemical data, was carried out in this study. Development of sandstone networks, as well as the presence of major and minor faults, was identified on 3D seismic data. Oil and gas migration were constrained by geochemical data, such as carbon isotope on gases collected at the sea bottom and fluid inclusion chemistry.
Understanding of the petroleum system was increased significantly by this kind of integration, although the deep-water area of the Naoetsu Basin still remains a frontier area for oil and gas exploration. It was found that the petroleum system active in the deep-water area of the Naoetsu Basin is very effective. Even though maturation of the source rock has occurred only since the Pliocene, oil and gas generated and migrated very rapidly, first horizontally along sandstone networks and then vertically through faults reaching a level just below the sea bottom, with the result that the hydrocarbon trap has leaked.
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Enhanced depositional and AVO models for lithologically complex sandstones in the Santos Basin, offshore Brazil
Authors Sabine Klarner, Bernhardt Ujetz and Rogério L. FontanaWhile exploring for hydrocarbons in rift-related basins, volcanic and volcaniclastic rocks and their erosional products are commonly encountered lithologies. At the reservoir level, the presence of rock types derived from volcanism or affected by post-volcanic re-deposition leads to highly varied complex lithologies with wide ranges of inherent rock properties.
In the Santos Basin, a number of exploration wells have encountered basalts emplaced along the basin hinge line that have controlled the sedimentation and basin geometry. The main reservoir units of the basin consist of complex Upper Cretaceous sandstones deposited during periods of active volcanism. For one of the main exploration targets, the Senonian Ilhabela Formation, integrated geological and geophysical interpretation of recently acquired seismic and well data has led to a refined sedimentological model, an enhanced AVO model as well as a deeper understanding of the petroleum system. The encountered sandstones are of shallow-marine and deltaic origin, with local occurrence of mafic volcanic and subvolcanic rocks. Dependent on the presence of volcanic rocks in the vicinity of the particular reservoir, two different types of sandstones with different AVO characteristics have been identified. The presence of volcanic rocks may be interpreted from seismic data by their distinct geometry, usually high amplitudes and unique AVO behaviour, expressed as a strengthening of positive amplitudes with increasing offset.
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Interpretation and mapping of a stratigraphic play using 3D seismic data and attributes in central Saudi Arabia
Authors Abdallah A. Al-Zahrani and Fernando NevesInterpretation of three-dimensional (3D) seismic data from the northern part of central Saudi Arabia allowed mapping of the Permo-Carboniferous Unayzah Formation's aeolian sand deposits and fluvial channels. These types of depositional environments have been associated frequently with better reservoir-quality sandstones within Saudi Arabia. The depositional setting of the Unayzah reservoirs can be highly variable and range from glacial, to lacustrine, to meandering fluvial, to aeolian, to braided stream. Seismic amplitude data were instrumental in mapping a truncation of the upper Unayzah reservoir against the overlying Pre-Khuff Unconformity. The use of seismic attributes, such as coherence and curvature, indicated the existence of faulting and a fluvial channel network at the top of the Unayzah Formation. The integration of well and seismic amplitude data, via acoustic impedance inversion, revealed the direction of potentially higher porosity fairways within the channel system. The structural and depositional architecture depicted in this study is being appraised through drilling of an exploration well.
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Integrating stratigraphic modelling and seismic interpretation: two practical examples
Authors M.-C. Cacas, J.-M. Laigle, E. Albouy and C. SulzerIn the future, the oil industry will have to exploit more and more complex sedimentary basins regarding sedimentology and tectonics. Basin studies will have to integrate more and more advanced and interrelated concepts from different disciplines. Fully integrated basin studies are not yet common practice, but some elements of an integrated workflow are starting to be proposed to the industry. These involve new computer modelling capabilities, such as computer-assisted seismic stratigraphy, 4D kinematic restoration, stratigraphic modelling and petroleum system modelling. Integration of seismic interpretation and sedimentology modelling is one element of this workflow which remains particularly challenging. Stratigraphic modelling is proposed to facilitate this integration; it consists of computerized forward simulation of sedimentary processes at basin scale and geological time-scale. A new simplified stratigraphic modelling method, based on the approximation of the sedimentary history by a succession of sequences during which the sedimentation is supposed to be steady state, will help to invert these stratigraphic models more easily. In particular, the results of seismic interpretation in terms of time-line interpretation and sedimentary environment can now be used as input data to the stratigraphic modelling procedure. The use of seismic data as validation data of the sedimentological model can also be considered, but their relevance depends largely on seismic modelling methods as well as input acoustic parameters.
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Carbonate production and stratigraphic architecture of shelf-margin wedges (Cretaceous, Vercors): lessons from a stratigraphic modelling approach
Authors Vanessa Teles, Rémi Eschard, Gisèle Etienne, Simon Lopez and Annie Arnaud-VanneauThis work was presented at the EAGE workshop in Grenoble. Its purpose was to illustrate a stratigraphic modelling approach on a single schematic 2D case and to discuss which sedimentary features are imaged on synthetic seismic sections at different frequencies. The Vercors plateau carbonate sequence, deposited during the Barremian to Early Aptian, was considered. Modelling hypotheses constrained mainly the depositional time length and the geometry of each sequence. In addition, it was assumed that most of the carbonates were produced in situ.
The stratigraphic modelling approach and lessons from the simulation results are presented, followed by a discussion of how stratigraphic modelling can be a helpful tool to validate or question the geological model. In order to reproduce the sequence geometries, rates of carbonate production needed to be changed between regressive and transgressive periods. Simulated sea-level changes do not match the geological estimations from field interpretation but they are in agreement with the magnitude of sea-level curve variations, with the exception of the early Barremian sequences. Qualitative and quantitative results from the model simulations help to question or validate the geological model. Stratigraphic modelling provides some insight into the way the carbonate system may have worked.
Secondly, for a smaller 2D geological model, several synthetic seismic sections were computed using wavelets of different dominant frequencies. The seismic sections are compared to underline what is imaged mainly at the different frequencies. The presence of two characteristic facies were also analysed. Results show the importance of some thin beds inside thick sequences and that certain sequence boundaries may not be visible at all.
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Stratigraphic modelling of turbidite prospects to reduce exploration risk
Authors Dave Waltham, Noah Jaffey, Stuart MacLean and Valentina ZampettiThis article presents an integrated workflow to model the evolution of ancient turbidity currents on a 3D structurally reconstructed palaeo-seafloor, allowing ancient turbidite sediment distributions to be estimated. Effective use of such approaches requires efficient model-inversion procedures so that model parameters (e.g. flow dimensions, densities etc.) can be estimated from any available data. It is shown that a directed Monte Carlo approach (i.e. a simple genetic search algorithm) is very effective. A case study of a Mesozoic prospect in the UK North Sea shows the power of these methods to discriminate between potentially attractive sediment-source locations. The main power of this approach lies in its ability to exclude many, otherwise attractive, sedimentation scenarios.
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Analysing exploration uncertainties by tight integration of seismic and hydrocarbon migration modelling
By Øyvind SyltaHigh success rates in the exploration for oil and gas can be achieved by incorporating best practice strategies in estimating the geological uncertainties from seismic data and geological models. A tight coupling of the seismic information and hydrocarbon migration modelling may allow for a consistent handling of uncertainties throughout the analysis. Seismic uncertainties include velocities used for depth conversion, the positioning of structural interpretations including faults, and assigning flow properties from seismic attributes. The necessary output from the seismic uncertainty analysis could be provided as uncertainty fields that may be used as input to hydrocarbon migration modelling.
The nonlinearity of the hydrocarbon migration process, including flow-path selection and trap phase filtering, frequently requires that local uncertainties are addressed in more detail. These uncertainties may require high-resolution seismic analyses in order to be further resolved. The structural interpretation is of particular importance to accumulation uncertainties, and fault juxtaposition and carrier dip direction uncertainty estimations can improve phase prediction estimates in exploration prospects. It is suggested that an improved best practice for exploration for oil and gas should include a tight coupling of the handling of uncertainties from seismic data in hydrocarbon migration modelling.
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Improved hydrocarbon charge prediction by source-rock modelling
Authors Are Tømmerås and Ute MannPredictions of initial source-rock distribution, thickness and quality are key input parameters to quantitative basin models. This article describes a workflow where process-based modelling of deposition and preservation of organic matter at basin scale is performed to provide the input to modelling of hydrocarbon generation and expulsion from source rocks. As the vertical resolution of the depositional- and source-rock models is significantly higher than for conventional basin models, a means of upscaling the source-rock properties is needed when providing these as input to hydrocarbon generation modelling.
To illustrate the modelling workflow, an example from the Triassic Kobbe Formation of the Norwegian Barents Sea was used. Two alternative source-rock models for the Kobbe Formation were constructed and discussed. During the modelling process preservation conditions were fine-tuned to better match local well data within the Nordkapp Basin. The second model provided a better calibration both for the source-rock model to the well data and for the secondary migration model to known hydrocarbon accumulations of the Nordkapp Basin.
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Volumes & issues
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Volume 30 (2024)
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Volume 29 (2023)
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Volume 28 (2022)
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Volume 27 (2021)
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Volume 26 (2020)
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Volume 25 (2019)
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Volume 24 (2018)
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Volume 23 (2017)
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Volume 22 (2016)
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Volume 21 (2015)
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Volume 20 (2014)
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Volume 19 (2013)
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Volume 18 (2012)
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Volume 17 (2011)
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Volume 16 (2010)
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Volume 15 (2009)
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Volume 14 (2008)
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Volume 13 (2007)
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Volume 12 (2006)
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Volume 11 (2005)
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Volume 10 (2004)
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Volume 9 (2003)
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Volume 8 (2002)
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Volume 7 (2001)
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Volume 6 (2000)
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Volume 5 (1999)
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Volume 4 (1998)
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Volume 3 (1997)
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Volume 2 (1996)
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Volume 1 (1995)