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- Volume 6, Issue 3, 2000
Petroleum Geoscience - Volume 6, Issue 3, 2000
Volume 6, Issue 3, 2000
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Use of 3D digital analogues as templates in reservoir modelling
Authors Ian Bryant, David Carr, Peter Cirilli, Nicholas Drinkwater, David McCormick, Peter Tilke and John ThurmondGeological analogues may be used to rigorously interpret three-dimensional (3D) subsurface reservoir geometry by combining the capabilities of graphics workstations with digital outcrop data collection. Digital data from sedimentary environments and outcropping geological formations are interpreted in a 3D viewing environment to construct 3D templates of analogues for reservoir bodies. These 3D geometries and associated scaling parameters are then available to build 3D digital hypotheses concerning subsurface reservoir geometries.
Two examples serve to illustrate this approach. Data from a modern fluvial system in the USA are used to construct digital templates. Interpretation of this dataset enables the relationship between 3D external geometries of sedimentary units to be rigorously defined and related to internal sedimentary structures. The location of gas-filled reservoir compartments in the Carboniferous Bend Conglomerate reservoirs of the Boonsville Field in North Texas are then interpreted using such analogue-derived digital templates.
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An assessment of steady-state scale-up for small-scale geological models
Authors Gillian E. Pickup and Karl D. StephenThe calculation of pseudo-relative permeabilities can be speeded up considerably by using steady-state methods. The capillary equilibrium limit may be assumed at small scales (30 cm or less), when the flood rate is low. At high flow rates and larger distance scales, we may use a viscous-dominated steady-state method which assumes constant fractional flow. Steady-state pseudos may also be calculated at intermediate flow rates using fine-scale simulations, and allowing the flood to come into equilibrium at different fractional flow levels. The aim of this paper is to assess the accuracy of steady-state scale-up for small-scale sedimentary structures.
We have tested steady-state scale-up methods using a variety of small-scale geological models. The success of steady-state scale-up depends not only on the flow rate, but also on the nature of the heterogeneity. If high permeability zones are surrounded by low permeability ones (e.g. low permeability laminae or bed boundaries), oil trapping may occur in a water-wet system. In this case pseudo-oil-relative permeabilities are very sensitive to flow rate, and care must be taken to upscale using the correct viscous/capillary ratio. However, in permeability models, where phase trapping may not occur (unconnected low permeability regions), the pseudos are similar, whatever the viscous/capillary ratio.
The disadvantage of steady-state scale-up is that it cannot take account of numerical dispersion, in the manner in which dynamic methods can. However, we show examples of coarse-scale simulations with viscous-dominated steady-state pseudos which agree favourably with fine-scale simulations. Provided there are sufficient grid blocks in the coarse-scale model, the smearing of the flood front due to numerical effects is not serious.
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Neogene wrench reactivation of the Barcoo Sub-basin, northwest Australia: implications for Neogene tectonics of the northern Australian margin
Authors Myra Keep, Anna Bishop and Ian LongleyThe Barcoo Sub-basin forms the southern part of the Browse Basin of Australia’s northwestern margin. Miocene reactivation of older Precambrian through Mesozoic-aged structures has resulted in a present-day complex right-lateral wrench zone. The fault system displays restraining and releasing bends separated by areas of almost pure strike-slip displacement, along its 180 km length. Reactivation and inversion varies along the system, with the southern end structurally highest, offsetting beds up to and including the seafloor. The location of restraining and releasing bends controls the occurrence of oil and gas shows in nine wells drilled in the sub-basin, with Neogene inversion causing trap leakage in a number of cases. Right-lateral motion on the Barcoo Fault system, in contrast to a proposed regional-scale left-lateral movement component on the northwestern margin as a whole, implies strong strain partitioning along the margin with regional tectonic control. We propose that the structural domain boundaries may be controlled in part by the location of the continental collision zone between the northernmost limit of Australian continental crust with the southernmost continental fragments of the Eurasian plate, in the vicinity of the island of Sumba.
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Synthetic seismic modelling of a large-scale geological cross-section from the Book Cliffs, Utah, USA
Authors David Hodgetts and John A. HowellSynthetic seismic sections have been generated from a 125 km long, depositional dip orientated cross-section compiled from outcrop data from the Book Cliffs of Eastern Utah, USA. These data are used to define the earth filter for a synthetic seismic section. An outcrop-based dataset has been used in preference to well data (though well data have been incorporated into the study section) because of the high confidence in the lateral continuity of data. The regional cross-section is modelled at 20, 50 and 100 Hz seismic source frequencies. As resolution increases, more laterally discontinuous reflections relating to facies terminations are imaged. Particularly important is the increase in internal reflections within each of the stratigraphic members (particularly the Sunnyside Member). These low angle clinoform events are imaged in low-resolution data but constructively interfere to form a lower number of more continuous looking events.
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Lower Cretaceous deep-water sandstone reservoirs of the UK Central North Sea
Authors S. W. Garrett, T. Atherton and A. HurstThe Lower Cretaceous deep-water depositional system of the Central North Sea is emerging as a significant economic target. It contains a broad range of sedimentary facies and architecture. Thick sands were deposited by high-density sediment gravity flows. Unusual banded and mixed slurried facies represent the products of processes transitional between turbidity currents and debris flows. Shale-prone units show evidence of debris flows and post-depositional down-slope movement. Geometrical architectural elements include narrow linear incised channels, broad linear sand-rich fairways, prograding sand lobes and laterally extensive sheets. Models for exploration and production are refined by core magnetic measurements, automated quantitative petrography, detailed structural analyses and biostratigraphical zonations. Key remaining challenges are refining depositional models to aid prediction of lateral facies variations, understanding trap mechanisms and geometry and improving images of sandstone units on seismic data.
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Deformation processes in the Britannia Field, UKCS
Authors J. R. Porter, R. J. Knipe, Q. J. Fisher, A. B. Farmer, N. S. Allin, L. S. Jones, A. J. Palfrey, S. W. Garrett and G. LewisThe intensity and distribution of deformation within cores recovered from 24 Britannia Field wells has been quantified and used to assess the sub-seismic deformation present. Structural logging has been amalgamated with microstructural and petrophysical analysis of fault rocks and the results used to construct models of the fluid flow behaviour of fault zones and to evaluate the correlations between core-scale structures and the larger-scale seismically mapped fault arrays. Deformation within Britannia is controlled primarily by (1) early sediment disruption, dewatering, detachment and folding in semi-lithified sediments and (2) more long-lived clustered arrays of small faults developed within fault damage zones. Fault population analysis illustrates that seismic-based mapping alone does not provide a good platform for accurately predicting the number of sub-seismic faults present. Analysis of the effect of deformation features on fluid communication highlights the importance of small-scale faults in enhancing communication in complex and initially separate sand bodies.
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Sand body geometry, constrained and predicted during a horizontal drilling campaign in a Lower Cretaceous turbidite sand system, Captain Field, UKCS Block 13/22a
Authors P. T. S. Rose, A. A. Manighetti, K. J. Regan and T. SmithThe Captain Field is a large viscous oil accumulation located in the Western Moray Firth, UK Block 13/22a which is being developed by long horizontal wells. The reservoir sand body geometry was defined in the appraisal phase by 20 vertical wells. Seismic attributes were not used because of the poor seismic signal to noise ratio in the reservoir interval. As the development drilling campaign has unfolded, the appraisal sand body geometry model has been significantly refined using a wealth of data from the horizontal wells.
During development drilling it has proved cheap to sidetrack horizontal well sections without a requirement to isolate the abandoned hole. This has resulted in significant extra geological data (e.g. top reservoir penetrations, sand thickness data). Integrating this dataset with top reservoir topography derived from seismic and weak internal reservoir seismic reflectors, the sand body geometry model is significantly improved in undeveloped parts of the field.
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The Kopervik fairway, Moray Firth, UK
The Albian–Aptian sand fairway in the Outer Moray Firth of the United Kingdom Continental Shelf, informally referred to as the Kopervik fairway, poses considerable challenges to the explorationist, but has the potential to generate significant commercial reward. After an initial spate of activity in the mid 1970s, the Kopervik Sandstone remained largely ignored as a primary exploration target until the late 1990s, despite its excellent reservoir quality and proven charge. This renewed exploration effort led to a number of successful discoveries. As a result of this activity – and a willingness among operators along the fairway to share information – a large regional database is developing. Drawing on this, we summarize our current and historical understanding of the fairway, using existing discoveries as examples.
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Controls on the Lower Cretaceous Punt Sandstone Member, a massive deep-water clastic deposystem, Inner Moray Firth, UK North Sea
Authors J. D. Argent, S. A. Stewart and J. R. UnderhillInterpretation of high-quality seismic data, constrained by exploration wells, provides insights into controls on the stratigraphic architecture and deep-water sedimentary processes that governed deposition of the Lower Cretaceous Punt Sandstone Member in the Inner Moray Firth Basin. We suggest a model of deposition in which sediment provenance from the north and west progressively filled depositional accommodation in proximal depocentres before spilling into more distal areas via linear, confined and incised channel complexes. As well as giving important clues into post-rift depositional processes in the basin, and a well-imaged ancient analogue for the deposition of massive deep-water sands, the seismic and stratigraphic data may also provide important insights into factors governing the poorly imaged Lower Cretaceous sands in neighbouring basins of the North Sea.
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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)