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- Volume 17, Issue 1, 2011
Petroleum Geoscience - Volume 17, Issue 1, 2011
Volume 17, Issue 1, 2011
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Field-scale geometries of Upper Khuff reservoir geobodies in an outcrop analogue (Oman Mountains, Sultanate of Oman)
Authors Bastian Koehrer, Thomas Aigner and Michael PöppelreiterABSTRACTThis paper provides data on the lateral continuity and geometry of potential reservoir geobodies in outcrops of Upper Khuff Formation time-equivalent strata in the Jebel Al Akhdar area (Oman Mountains, Sultanate of Oman). It presents outcrop-based quantitative data of shoal-associated grainstone bodies in a sequence stratigraphic framework on the scale of an average Khuff gas field. Such data may be useful for correlation and modelling of subsurface reservoirs.
A stratigraphic correlation of five outcrop sections, based on facies, sequence analysis and gamma-ray pattern, was used as a framework for mapping the distribution and lateral extent of grainstone geobodies over an area of 8 × 8 km. Four grainstone bodies were traced laterally along distinct marker beds over several hundreds of metres.
The stratigraphic architecture shows a general layer-cake pattern. The thickness and lateral extent of reservoir geobodies is strongly influenced by their stratigraphic position. High-energy shoal facies developed preferentially in the regressive parts of cycles of multiple hierarchies. Individual grainstone bodies may reach a thickness of 6 m, and those thicker than 3 m extend across the area of interest. Clinoforms or shingle-type geometries were explicitly searched for, but were not present.
The observed systematic variations in extent and two-dimensional sedimentary architecture of Khuff grainstone bodies were used as input for 3D static facies modelling. Outcomes of this study have been used to reduce uncertainty on grainstone geometries, production-scale correlation strategies and definition of lateral facies successions in subsurface models of the Khuff reservoir.
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Geological modelling and history matching of multi-scale flow barriers in channelized reservoirs: methodology and application
Authors Hongmei Li and Jef CaersABSTRACTThe key problem addressed in this paper arises in the situation where multi-scale shale drapes are present along channel, channel-belt and/or valley-bounding surfaces, but the channel location is uncertain or unknown. In order to reduce this uncertainty, the channel and drape locations should be modified in order to calibrate the flow response to the historic production data as well as any static data from wells. We propose a coupled geological modelling and history-matching method in which the reservoir architecture composed of channels is simulated with a pre-defined stacking pattern, then the shale drapes are simulated along the bounding surfaces using a multiple-point statistics technique and, finally, channel and scour-hole locations are gradually perturbed until the corresponding flow responses match the field production data. The perturbation during the history matching must be geologically consistent, i.e. the result must honour the observed individual channel geometries and the interpreted channel stacking patterns.
A digital 3D model representing a real field in offshore West Africa was studied to demonstrate this modelling and history-matching approach in which the multi-scale shale drapes are simulated and perturbed while the reservoir geological concepts are preserved and the well data are honoured. The final history-matched geological models have better prediction power than geological models built with randomly selected input parameters.
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Retaining geological realism in dynamic modelling: a channelized turbidite reservoir example from West Africa
Authors Faruk O. Alpak, Mark D. Barton and David CastineiraABSTRACTA comprehensive simulation study tested and analysed the sensitivity of dynamic connectivity in turbidite channel reservoirs to a large number of stratigraphic and engineering parameters. The study showed that subseismic shale architecture has a significant effect on reservoir connectivity. However, representing the complete spectrum of fine-scale architectural details in full-field simulation models is beyond the limits of existing computational capabilities. Previous work demonstrated that incorporating geologically based pseudo-relative permeabilities into relatively coarse full-field reservoir models renders practically intractable simulation cases tractable. We developed a methodology for generating pseudo-relative permeabilities at multiple geological scales, incorporating the effect of channel architecture and reservoir connectivity into fast simulation models.
We describe a dynamic modelling workflow that integrates geologically based pseudo-relative permeabilities into a two-stage automatic history-matching algorithm. The history-matching problem is posed as one of data conditioning in the Bayesian framework. We show the application of the workflow to a channelized turbidite reservoir in West Africa. It is demonstrated that multiple geologically consistent models that are conditioned to production data can be generated rapidly thanks to optimally coarse simulation models that capture the effect of subseismic channel architecture on recovery behaviour, and run efficiently as the forward model within a Bayesian inference framework. Proof-of-concept tests carried out using field data indicate that the history-matched models predict well-by-well future recovery response with good accuracy.
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Quartz cementation in mudstones: sheet-like quartz cement from clay mineral reactions during burial
Authors Brit Thyberg and Jens JahrenABSTRACTPetrographic evidence of thin sheet-like or platelet-shaped quartz cement parallel to bedding is documented in deeply buried, originally smectite-rich, Late Cretaceous mudstones from well 6505/10-1 in the Vøring Basin, offshore Norway. The platelets are mainly built up of areas of patchy continuous quartz cement with various amounts of earlier-formed interlocking microquartz crystals. Cathode luminescence (CL) spectra confirm an authigenic origin for the quartz cement. The quartz platelets may originate as flakes (at c. 90–100 °C) that may evolve into well-developed near-continuous patchy quartz cement identified at 4300 m/150 °C. The quartz cement is probably sourced from silica released by the clay dissolution-precipitation processes (smectite and smectite/illite to illite and kaolinite to illite). At temperatures above about 90–100 °C, the continuous supply of silica from these clay mineral reactions results in precipitation of quartz flakes and sheet-like quartz cement. The quartz sheets may act as a mudrock stiffening agent, reinforcing and further cementing together the microquartz networks and aggregates and possibly also enhancing the schistosity and anisotropy of these mudstones during increasing burial. The quartz sheets may also act as vertical permeability barriers in the sediment possibly contributing to overpressure formation during chemical compaction.
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An outcrop-based comparison of facies modelling strategies in fan-delta reservoir analogues from the Eocene Sant Llorenç del Munt fan-delta (NE Spain)
ABSTRACTSedimentary facies is a key control on petrophysical properties within subsurface reservoirs and facies modelling is a critical aspect of reservoir modelling. Several modelling methods exist and selecting the best approach for a specific case is challenging and time-consuming. Outcrop analogues provide detailed information on architecture, geometry and facies connectivity that is not directly available in the subsurface. By modelling outcrop data it is possible to test and compare different modelling strategies systematically in a case where the geology is well constrained. The Eocene aged, Sant Llorenç del Munt fan-delta complex (NE Spain) is a well exposed, transgressive–regressive fan-delta. Outcrop data were used to test a variety of modelling strategies in which the density of conditioning wells, stratigraphic subdivision, modelling algorithm and trends were all varied. The results of these modelling exercises were compared against themselves and against a close-to-deterministically built Base Case reconstruction using a series of static measures including the distribution of fan-delta front reservoir facies, directional connectivity and reservoir-to-well connectivity.
The results highlight the following: (a) the impact of the conditioning well density on improving the stratigraphic architecture reproduction in the different modelling approaches; (b) that surface-based modelling subdivisions including the maximum flooding surface to separate independent grids for modelling the transgressive and regressive sequence sets can be detrimental when compared to using only the top and base of the composite sequence unless additional constraints are included; (c) that an algorithm combining a linear trend and a Gaussian field is the most suitable algorithm for reproducing this type of architecture, but requires defining a 3D trend; and (d) the need for using trends to reproduce the architecture when well data are sparse. These results provide guidelines for modelling analogue fan-delta reservoirs in the subsurface.
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An integrated geophysical investigation of Haymana Basin and hydrocarbon prospective Kirkkavak Formation in Central Anatolia, Turkey
More LessABSTRACTIn this study, all available geological, geophysical and geochemical data were integrated to assess the hydrocarbon prospectivity of the Haymana Basin, an interior basin in Central Anatolia. First, the basin was modelled in three dimensions (3D) using gravity data which identified the deepest part of the basin to the east of Haymana, south of Ankara. This potential hydrocarbon generation area has not been properly explored. Next, the first order vertical derivative of the gravity anomaly map was computed to identify boundaries of prospective structures from inflections in the gravity gradient. Aeromagnetic data were transformed to an analytical signal to identify the probable locations of buried magmatic intrusions. The prospective part of the Haymana Basin was interpreted as being located to the east of an intrusion.
Finally, all available geochemical data of the Kirkkavak Formation were classified for different parameters (TOC, S1+S2 and Tmax) and maximum values of each parameter were mapped. In comparing the 3D depth model with individual geochemical maps, it was observed that each geochemical parameter was consistent with the interpreted prospective zone of the Haymana Basin.
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Seismic imaging of sub-circular salt-related structures: evidence for passive diapirism in the Straits of Hormuz, Persian Gulf
Authors Mohammad Alsouki, Mohammad Ali Riahi and Ali YassaghiABSTRACTA detailed interpretation of seismic data has been carried out to analyse salt diapirism in the Straits of Hormuz in the Persian Gulf. Salt diapirs in the Zagros Foldbelt are mainly characterized by structures formed by mobilization of the Cambrian Hormuz salt as reactive diapirs during the Late Cretaceous–Tertiary Zagros orogeny. Interpretation of available data in the straits of Hormuz suggests that diapirs of Hormuz salt grew actively until the Early Miocene and then continued to rise passively by downbuilding of surrounding sediments until the present time. The syn- to post-Miocene Zagros sedimentation played a major role in passive diapirism. Sedimentation of the thick Lower Miocene deposits led to greater subsidence of the basin and passive diapirism of the Early Miocene Fars salt as well as further inflation of the Hormuz salt into neighbouring structures. Seismic mapping of the salt-related structures as well as observations in the overlying sediments, such as thickness variations and faulting, also constrain the Late Tertiary passive diapirism of the Hormuz and Fars salt in the Zagros.
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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)