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  • 1
    Keywords: river system ; reservoirs ; geological timescale ; fluvial system ; deposits
    Description / Table of Contents: 4 January 2019 --- Accepted manuscript Describing Fluvial Systems: linking processes to deposits and stratigraphy / Jim Best and Christopher R. Fielding / Geological Society, London, Special Publications, 488, https://doi.org/10.1144/SP488-2019-056 --- 20 December 2018 --- Accepted manuscript Eocene-Recent drainage evolution of the Colorado River and its precursor: an integrated provenance perspective from SW California / Uisdean Nicholson, Andrew Carter, Paula Robinson and David I.M. Macdonald / Geological Society, London, Special Publications, 488, https://doi.org/10.1144/SP488-2019-272 --- 18 December 2018 --- Stochastic modelling of flow sequences for improved prediction of fluvial flood hazards / Sandhya Patidar, Deonie Allen, Rick Haynes and Heather Haynes / Geological Society, London, Special Publications, 488, 18 December 2018, https://doi.org/10.1144/SP488.4 --- 17 December 2018 --- Effect of dynamically varying zone-based hedging policies on the operational performance of surface water reservoirs during climate change / Adebayo J. Adeloye and Bankaru-Swamy Soundharajan / Geological Society, London, Special Publications, 488, 17 December 2018, https://doi.org/10.1144/SP488.1 --- 14 December 2018 --- Understanding subsurface fluvial architecture from a combination of geological well test models and well test data / Patrick William Michael Corbett and Gleyden Lucila Benítez Duarte / Geological Society, London, Special Publications, 488, 14 December 2018, https://doi.org/10.1144/SP488.7 --- 10 December 2018 --- Natural and anthropogenic influences on the Nhecolândia wetlands, SE Pantanal, Brazil / Emiliano Castro de Oliveira, Sila Pla-Pueyo and Christopher R. Hackney / Geological Society, London, Special Publications, 488, 10 December 2018, https://doi.org/10.1144/SP488.5 --- 29 November 2018 --- Spatial variations in distributive fluvial system architecture of the Upper Cretaceous Marília Formation, SE Brazil / Patrick Führ Dal’ Bó, Marcus Vinícius Theodoro Soares, Giorgio Basilici, Amanda Goulart Rodrigues and Mauricius Nascimento Menezes / Geological Society, London, Special Publications, 488, 29 November 2018, https://doi.org/10.1144/SP488.6 --- 28 November 2018 --- Towards the multi-scale characterization of braided fluvial geobodies from outcrop, core, ground-penetrating radar and well log data / Luis Miguel Yeste, Saturnina Henares, Neil McDougall, Fernando García-García and César Viseras / Geological Society, London, Special Publications, 488, 28 November 2018, https://doi.org/10.1144/SP488.3 --- 21 November 2018 --- Sedimentology, architecture and depositional setting of the fluvial Spireslack Sandstone of the Midland Valley, Scotland: insights from the Spireslack surface coal mine / R. Ellen, M. A. E. Browne, A. J. Mitten, S. M. Clarke, A. G. Leslie and E. Callaghan / Geological Society, London, Special Publications, 488, 21 November 2018, https://doi.org/10.1144/SP488.2
    Edition: online first
    Language: English
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  • 2
    Publication Date: 2016-05-14
    Description: Coquinas are significant producing facies in the pre-salt reservoirs of Brazil and Angola. This paper describes an analogue model study to help understand the reservoir characterization of coquina reservoirs. Porosity and permeability measured in 39 core plugs from a single coquina bed in a Lower Cretaceous outcrop in NE Brazil have been combined in a three-dimensional geological model for use in reservoir simulation. A training image derived from the geometry of a Holocene coquina analogue in Western Australia controlled the distribution of the bed-scale petrophysical properties from the outcrop. A synthetic well test showed that the effective permeability of the system lies between the geometrical and harmonic averages of the plug data in the layer. There is also moderate flow anisotropy, with preferential fluid flow aligned along the beach ridges. This paper demonstrates how the combination of outcrop data and an appropriate modern environment might be used to improve our understanding of the behaviour of coquina reservoirs and to guide future reservoir studies.
    Print ISSN: 1354-0793
    Topics: Chemistry and Pharmacology , Geosciences
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  • 3
    Publication Date: 2014-11-25
    Description: Analytical well-test solutions are mainly derived for simplified and idealized reservoir models and therefore cannot always honour the true complexity of real reservoir heterogeneities. Pressure transients in the reservoir average out heterogeneities, and therefore some interpretations may not be relevant and could be misleading. Geological well testing refers to the numerical simulation of transient tests by setting up detailed geological models, within which different scales of heterogeneity are present. The concept of geological well testing described in this paper assists in selecting from multiple equi-probable static models. This approach is used to understand which heterogeneities can influence the pressure transients. In this paper, a low-energy multi-facies fluvial reservoir is studied, for which data from a well test of exceptionally long duration are available. The pervasive low reservoir quality facies and restricted macro cross-flow between the reservoir layers give rise to an effective commingled system of flow into the wellbore (i.e. zero or very low vertical cross-flow between the reservoir units). In our model, facies transitions produce lateral cross-flow transients that result in a ‘double-ramp-effect’ signature in the test response. A sophisticated multi-point statistical (MPS) facies modelling approach is utilized to simulate complex geological heterogeneities and to represent facies spatial connectivity within a set of generated static models. The geological well-test model responses to a real well-testing cycle are then evaluated using dynamic simulation. The pressure match between simulated and recorded data is improved by generating multiple facies and petrophysical realizations, and by applying an engineering-based hybridization algorithm to combine different models that match particular portions of the real well-test response. In this example, the reservoir dynamics are controlled by subtle interaction between high-permeability channels and low-permeability floodplain deposits. Effective integration of geology and dynamic data using modern methods can lead to better reservoir characterization and modelling of such complex reservoir systems.
    Print ISSN: 1354-0793
    Topics: Chemistry and Pharmacology , Geosciences
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  • 4
    Publication Date: 2018-12-15
    Description: Two decades of geological modelling have resulted in the ability to study single-well geological models at a sufficiently high resolution to generate synthetic well test responses from numerical simulations in realistic geological models covering a range of fluvial styles. These 3D subsurface models are useful in aiding our understanding and mapping of the geological variation (as quantified by porosity and permeability contrasts) in the near-wellbore region. The building and analysis of these models enables many workflow steps, from matching well test data to improving history-matching. Well testing also has a key potential role in reservoir characterization for an improved understanding of the near-wellbore subsurface architecture in fluvial systems. Developing an understanding of well test responses from simple through increasingly more complex geological scenarios leads to a realistic, real-life challenge: a well test in a small fluvial reservoir. The geological well testing approach explained here, through a recent fluvial case study in South America, is considered to be useful in improving our understanding of reservoir performance. This approach should lead to more geologically and petrophysically consistent models, and to geologically assisted models that are both more correct and quicker to match to history, and thus, ultimately, to more useful reservoir models. It also allows the testing of a more complex geological model through the well test response.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 5
    ISSN: 1573-8868
    Keywords: semivariograms ; sedimentary structure ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Clastic sediments may have a strong deterministic component to their permeability variation. This structure may be seen in the experimental semivariogram, but published geostatislical studies have not always exploited this feature during data analysis and covariance modeling. In this paper, we describe sedimentary organization, its importance for flow modeling, and how the semivariogram can be used for identification of structure. Clastic sedimentary structure occurs at several scales and is linked to the conditions of deposition. Lamination, bed, and bedset scales show repetitive and trend features that should be sampled carefully to assess the degree of organization and levels of heterogeneity. Interpretation of semivariograms is undertaken best with an appreciation of these geological units und how their features relate to the sampling program. Sampling at inappropriate intervals or with instruments having a large measurement volume, for example, may give misleading semivariograms. Flow simulations for models which include and ignore structure show that the repetitive features in permeability can change anisotropy and recovery performance significantly. If systematic variation is present, careful design of the permeability fields therefore is important particularly to preserve the structure effects.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Sandbodies from storm-dominated marine and marginal marine environments commonly contain intervals of laminated fine sandstones. A characteristic of such lamination is the presence of low angle cross lamination. In order to model correctly the effects of such lamination on a waterflood of an oil-bearing shoreface sequence it was necessary to quantify the geometry of the laminaset elements.This challenge has been greatly complicated by the lack of outcrop of the formation of interest. The Middle Jurassic Rannoch Formation of the North Sea only occurs in the subsurface where it is not possible in core to measure the aspect ratio of laminasets directly. In this study, the laminaset geometry data that can be obtained from core (e.g. apparent set thicknesses) were collected for the Rannoch Formation. These data were compared with similar data from potential outcrop analogues in (1) the Cretaceous Kennilworth Member of the Blackhawk Formation in Utah, USA and (2) the Upper Jurassic Bencliff Grit from the Dorset coast, UK.A quantitative analysis of laminaset geometries has been used to compare subsurface core with potential outcrop analogues. The Rannoch Formation core is characterized by numerous low angle truncations. We have measured these features in two wells (means of 7.2° and 12.1°). Mean apparent set thicknesses were 0.24 and 0.19 m.In the outcrop sections studied, truncation angles ranged from 9.6° to 13.4° and mean set thicknesses from 0.24 to 0.34 m. Mean bounding surface dips of 5.8° and 8.6°, and mean laminaset lengths of 2.3 and 4.1 m were also measured. directly in the field and by using photomosaics.On the basis of this comparison, the Kennilworth Member in Utah was found to be the most suitable and the geometries (i.e. aspect ratios) measured there were used to generate an appropriate geometry of Rannoch laminaset geometries for use in engineering studies: laminaset length, 2.0 m; laminaset thickness, 0.2 m.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2012-02-01
    Description: Well testing is a critical part of any evaluation of a carbonate reservoir discovery. Well-test interpretation in carbonate reservoirs poses additional challenges to those normally faced in the interpretation process in clastic reservoirs. The range of different boundary and crossflow relationships that are generated during well testing by the complex porosity systems are often poorly quantified and understood. The volume over which the pressure response is effective is also a source of great uncertainty and could be critical at the exploration/appraisal stage in any project.In this paper, which describes a generic modelling approach, we consider carbonate reservoirs which contain three pore sytems (or porosity types): (1) microporosity (end-member) with low permeability and high porosity; (2) macroporosity (end-member) with high permeability and high porosity; and (3) fracture porosity with high permeability and low porosity. These occur in various nested geometrical distributions and varying contrasts. The observed well-test responses (i.e. fracture flow, fracture–matrix interactions) tend to ‘obscure’ one of these systems when compared with theoretical models. Micro- (meso-) and macroporosity can merge into a single matrix porosity system where the permeability contrasts are not great and the correlation lengths short (which can often be the case in carbonates). Macroporosity can also appear in well testing to ‘merge’ with the fracture response, i.e. the contributions of flow in the fractures and (high-permeability) porous matrix are indistinguishable. As a result of the homogenizing attributes of pressure dissipation away from the well, it is not generally possible to see the effects of a ‘triple-porosity’ response (i.e. where three different pore systems have a separate and identifiable signature on the well-test response) and a classical double-porosity response in the well test, despite three different pore systems being present, is possible. The apparent double-porosity response, which might obscure a triple-porosity system, therefore needs careful interpretation in order to attribute the appropriate properties during reservoir characterization in carbonates.In this work we use ‘geological’ well testing (i.e. well testing through numerical simulation of hypothetical geological models) to systematically analyse the effects of microporosity, macroporosity and fracture porosity on pressure dissipation and their apparent homogenization. While recent studies have proposed that a triple-porosity system should result in a ‘W-shaped’ response, we do not observe this behaviour in our simulations, although we specifically designed our geological models with a triple-porosity system. Instead we observe how macroporosity merges with the fractures or micro- and macroporosity merge, creating a ‘sub-dominant’ matrix or a ‘dominant’ fracture system, respectively and follow a traditional ‘V-shaped’ double-porosity response.
    Print ISSN: 1354-0793
    Topics: Chemistry and Pharmacology , Geosciences
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  • 8
    Publication Date: 2018
    Description: 〈p〉Two decades of geological modelling have resulted in the ability to study single-well geological models at a sufficiently high resolution to generate synthetic well test responses from numerical simulations in realistic geological models covering a range of fluvial styles. These 3D subsurface models are useful in aiding our understanding and mapping of the geological variation (as quantified by porosity and permeability contrasts) in the near-wellbore region. The building and analysis of these models enables many workflow steps, from matching well test data to improving history-matching. Well testing also has a key potential role in reservoir characterization for an improved understanding of the near-wellbore subsurface architecture in fluvial systems. Developing an understanding of well test responses from simple through increasingly more complex geological scenarios leads to a realistic, real-life challenge: a well test in a small fluvial reservoir. The geological well testing approach explained here, through a recent fluvial case study in South America, is considered to be useful in improving our understanding of reservoir performance. This approach should lead to more geologically and petrophysically consistent models, and to geologically assisted models that are both more correct and quicker to match to history, and thus, ultimately, to more useful reservoir models. It also allows the testing of a more complex geological model through the well test response.〈/p〉
    Print ISSN: 0375-6440
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 9
    Publication Date: 2018-01-17
    Print ISSN: 1354-0793
    Electronic ISSN: 2041-496X
    Topics: Chemistry and Pharmacology , Geosciences
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