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- Volume 3, Issue 2, 1997
Petroleum Geoscience - Volume 3, Issue 2, 1997
Volume 3, Issue 2, 1997
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The Carboniferous of Western Europe; the development of a petroleum system
A consistent stratigraphic study of the western European Carboniferous Basin has allowed the generation of eight palaeogeographic timeslices. These illustrate a model of large scale eastern (dextral) tectonic escape on the northern side of a convergent margin and integrate the diverse tectonic and sedimentary settings observed within the basin as a whole. This model can be compared to the present day eastern Mediterranean, where a similar range of diverse tectonic settings are observed. Reservoir and source distribution is discussed for each time-slice along with the present distribution of Carboniferous oil and gas fields. Due to the diversity observed no unique play type can be distilled from the data to explain the distribution of hydrocarbons within the studied area.
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The NE Atlantic margin; implications of late Mesozoic and Cenozoic events for hydrocarbon prospectivity
Authors A. G. Dore, E. R. Lundin, O. Birkeland, P. E. Eliassen and L. N. JensenThe study takes in the entire NE Atlantic margin (NEAM) but emphasizes the sparsely drilled More and Voring Basins. A network of Permo-Triassic and Jurassic basins was strongly overprinted by younger extensional episodes. At least three phases are probable--early Cretaceous, mid-Cretaceous and latest Cretaceous-early Eocene--between the late Jurassic and break-up. Substantial thicknesses of Cretaceous and Cenozoic strata along the margin have focused exploration interest on the late Cretaceous and Paleocene intervals as easily drillable targets. Reservoirs within these intervals were deposited as gravity-driven sand incursions into an overwhelmingly mud-prone environment. Sand pulses of Albian-Coniacian, Santonian-early Campanian and Paleocene age occur widely, and can be tied to the tectonic episodes. Vertical migration of hydrocarbons from known Jurassic source rocks is proven west of Shetlands, but in many parts of the margin remigration from intermediate reservoirs would be required to charge the shallower plays. Failing this, prospectivity will hinge on the presence of frontier source rocks, with best possibilities at Barremian, Aptian-Albian, Cenomanian-Turonian and Paleocene levels. Potential hydrocarbon traps were formed by pre-breakup extensional faulting and by post-breakup compression.
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Illite dates record deep fluid movements in petroleum basins
Authors D. Darby, M. Wilkinson, A. E. Fallick and R. S. HaszeldineK-Ar age dates of authigenic illite from sandstones in the UK south Central Graben have a bimodal distribution. In contrast to established hypotheses of thermal triggers, this illite growth is explained by changes in hydrogeological history. Fluid motion during burial can hence be dated. Illite growth at 84-58 Ma on the graben margins was coincident with rapid subsidence of the Graben axis and consequent expulsion of pore fluids onto the margins. This event pre-dated both overpressure, and the secondary migration and accumulation of hydrocarbon in the region. Illite growth was probably caused by increased solute transport rates during pore fluid motion. Illite growth on an axial high (33-30 Ma) occurred during overpressured conditions. This was triggered either by: (1) downward fluid migration as a consequence of overpressure release. These fluids carried carboxylic acids or hydrocarbons from the highly overpressured Kimmeridge Clay Formation into the less pressured Fulmar Sandstone Formation; or (2) a decrease in water-rock ratios as fluid flow declined within the sandstones, as a consequence of overpressure build-up. Published experiments show that illite growth is favoured by low water-rock ratios.
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The Predobrogean Depression in Romania and Moldova and its hydrocarbon prospects
Authors Vasile Moroz, Vasile Neaga, Pamfil Polonic and Vlad RoscaThe Predobrogean Depression contains a Precambrian to Triassic sequence many kilometres thick, overlain unconformably by Middle and Jurassic strata 2 km thick, which are capped by a thin Cretaceous-Neogene cover. The depression lies southwest of the East European Platform and northeast of the Hercynian-Kimmerian North Dobrogea orogen. No significant hydrocarbon finds have been made. Scattered wells show bituminous clays at Vendian and Devonian levels and bitumen or hydrocarbon shows occur in Devonian dolomites, Permian Greywackes, Triassic sandstones and Jurassic strata. Minor oil and gas finds have been made in Neogene reservoirs but the main prospectivity is assessed to be in the Palaeozoic formations. Seismic data quality must be improved to reveal the structure of the Palaeozoic section.
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Extrapolating fracture orientations from horizontal wells using stress trajectory models
Authors K. Rawnsley, V. Auzias, J. P. Petit and T. RivesThis paper presents a recently developed approach for extrapolating fracture orientations from horizontal wells. It is commonly accepted that tension fractures propagate perpendicular to the minimum principal stress. The hypothesis has been tested that in some cases, by modelling the stress trajectories within a faulted compartment, it is possible to reproduce the orientations of the tension fractures. The stress trajectory models we present are based on photo-elastic techniques. The models are first calibrated against outcrop fracture patterns and are subsequently applied to a reservoir database consisting of a 3D seismic block and a horizontal well with almost complete FMS image coverage. The results show that tension fractures may show perturbed orientations in the vicinity of faults. It is shown that by appropriate characterization of the seismic and well fracture data, it may be possible to use stress trajectory models to predict fracture orientation in a reservoir.
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Prospective Palaeozoic reefs in the southern part of the Barents Sea shelf
More LessPalaeozoic carbonate build-ups have been identified from seismic data in the south of the Barents Sea Shelf at several stratigraphic levels: Upper Permian mainly in the west of the Barents Shelf, Lower Permian (Asselian-Artinskian), Carboniferous, Upper Frasnian-Famennian, Lower Frasnian, Lower Devonian, Silurian and probably Ordovician. Most of build-ups are identified in the southern part of the offshore the Pechora Platform (the Varandey-Adzvinskaya Structural Zone, Pechora-Kolvinskiy Aulacogen, Seduyakhinskiy Ridge). Large Late Devonian reefs, apparently of barrier type, are seen in the east of the Korginskiy High. Small carbonate build-ups are seen in the Carboniferous-Permian section in the Kola-Kanin Monocline and the West Kola Saddle, where a wide zone of reefs formed which appear to extend to the west to the Finnmark Platform. The wide extension of Palaeozoic reefs in the south of the Barents Sea Shelf, including the Pechora Shelf, increases the petroleum potential in the region.
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The application of network modelling techniques to multiphase flow in porous media
Authors S. R. McDougall and K. S. SorbieA review of the utility of network models is presented to describe multiphase flow at the pore-scale. Precise details of each set of simulations can be found in the appropriate reference and only the most pertinent results are presented here. The main aim of this paper is to highlight the effectiveness of network models as interpolative and interpretative numerical tools. Both primary and secondary capillary-dominated, two-phase displacements are considered and well-documented hysteresis effects are successfully reproduced. Waterfloods of mixed-wet media are subsequently described and associated variations in relative permeability and recovery efficiency reported. Optimum recovery is obtained from networks containing a 50-50 mix of oil-wet and water-wet pores. Finally, a discussion of unsteady-state drainage and imbibition models follows and these are applied to waterfloods in finely-laminated porous media. Results highlight the complex interactions between capillary forces, viscous forces and geological structure.
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Application of surface prospecting methods in the Dutch North Sea
Authors Martin G. Baum, Karl-Heinz Bleschert, Manfred Wagner and Manfred SchmittThe characterization of invisible hydrocarbon micro-seepage intensities in surface sediments is used to evaluate subsurface hydrocarbon potential. A cost-effective multidisciplinary surface prospecting method, termed "BIG", is employed as a supplementary instrument to conventional exploration tools to assess the remaining prospectivity of a licence tract in the Dutch North Sea. Microbial investigations, molecular and isotopic gas characterization as well as UV fluorescence measurements are utilized for direct hydrocarbon detection in surface sediments. The definition and distribution of anomalous intensities is used as an index for the hydrocarbon potential in the deeper sub-surface. In combination with seismic information the BIG method can help to reduce exploration risk. It proves to be an effective instrument to determine the lateral extent of liquid hydrocarbon migration and to localize areas of prospective potential. This case history covers a successful application of the BIG method to investigate undetected hydrocarbon potential in an established producing province.
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Qarn Alam; the design of a steam-injection pilot project for a fractured reservoir
Authors M. Hartemink, B. M. Escovedo, J. E. Hoppe and R. MacaulayIn July 1996 a steam-injection pilot project was initiated in the Qarn Alam field in Oman. The objective is to test the steam-enhanced gas-oil gravity drainage of the heavy oil remaining in the matrix of the fractured carbonate Shuaiba reservoir. This paper presents the results of reservoir simulations that were conducted to investigate design and future interpretation of the steam pilot. Different simulation techniques were applied to describe the complexity of thermal processes and multiphase flow in a densely fractured reservoir. Pilot performance and areal advance of the steam zone were investigated. The possibility of oil rim lowering, prior to injecting steam, and of injecting steam in two different local crests, were also investigated but rejected on the basis of simulation results. Finally, locations for steam injection wells and pilot observation wells are proposed and requirements for pilot monitoring deduced.
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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)