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- Volume 22, Issue 2, 2016
Petroleum Geoscience - Volume 22, Issue 2, 2016
Volume 22, Issue 2, 2016
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Integration of Cretaceous Morro do Chaves rock properties (NE Brazil) with the Holocene Hamelin Coquina architecture (Shark Bay, Western Australia) to model effective permeability
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.
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Fault linkage across weak layers during extension: an experimental approach with reference to the Hoop Fault Complex of the SW Barents Sea
More LessA series of analogue experiments utilizing sequences of sand with interlayered silicone polymer have been performed to investigate the effects of multistage extension on rock sequences of different strength, with particular reference to the Hoop Fault Complex of the Barents Sea.
It was found that the width and style of the graben systems as seen in map view depend strongly on the extension velocity. Wide areas of graben formation are promoted by fast extension, whereas narrowly constrained deep-graben structures are typical of slow extension rates. Furthermore, the decoupling strata are likely to be characterized by flow rather than by distinct detachment faults.
The scaled experiments produced units of contrasting fault frequencies and styles in individual sand layers positioned between layers of silicone polymer. It was also found that the fault segments developed from different levels were related to varying extents (hard-linked, soft-linked, firm-linked, unlinked).
The fault configurations and the general fault pattern obtained in the experiments is similar to that observed in natural faults where salt or unconsolidated mudstone separate sequences of sand.
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Variability and heterogeneity of the petrophysical properties of extensional carbonate fault rocks, Malta
Authors E. A. H. Michie and T. J. HainesSelected carbonate-hosted normal fault zones on the island of Malta have been analysed to assess the potential impact of fault rocks on fluid flow (i.e. fault seal). Fault displacement ranging from <1 to 90 m has allowed systematic investigation of the evolution of fault-rock types, distribution and properties with increasing displacement. The focus has been on examining locations of fault-rock formation, because this significantly affects fluid-flow pathways across and along faults, and the types of fault rock formed. The location of fault rock is dependent on the fault-zone architecture. Fault zones on Malta have architectures with multiple slip surfaces within weaker carbonate layers, distributing fault rock onto several slip surfaces. This distribution prevents formation of a continuous fault core, particularly at lower displacements (<30 m). The discontinuous fault core causes these faults to be transmissive, allowing fluids to flow across the fault. The hydraulic behaviour is also a function of the deformation mechanisms active in the formation of fault rocks. Lithological heterogeneity in a faulted carbonate succession leads to a variety of deformation mechanisms, generating up to nine different fault-rocks types with a range of deformation microstructures along a single slip surface. The type of fault rock formed is a function of the host rock texture, juxtaposition, displacement and deformation conditions. Each deformation microstructure has different petrophysical properties, causing the porosity and permeability to vary along-strike and downdip on any slip surface, affecting the fault’s hydraulic behaviour. The extent of the poroperm variation depends on lithofacies juxtaposition and displacement: juxtaposition of similar lithofacies reduces poroperm variation and juxtaposing different lithofacies at higher displacements (>30 m) increases the range of poroperm.
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Petrophysical and numerical seismic modelling of CO2 geological storage in the E6 structure, Baltic Sea, offshore Latvia
Authors Kazbulat Shogenov, Davide Gei, Edy Forlin and Alla ShogenovaTime-lapse numerical seismic modelling based on rock physics studies was for the first time applied to analyse the feasibility of CO2 storage monitoring in the largest Latvian offshore geological structure E6 in the Baltic Sea. The novelty of this approach was the coupling of the chemically induced petrophysical alteration effect of CO2-hosting rocks measured in laboratory with time-lapse numerical seismic modelling. Synthetic seismograms were computed for the E6 structure, where the sandstone reservoir of the Deimena Formation of Cambrian Series 3 (earlier Middle Cambrian) was saturated with different concentrations of CO2. The synthetic seismograms obtained after CO2 injection were compared with the baseline. The following four scenarios were considered: (1) a uniform model without the alteration effect; (2) a uniform model with the alteration effect; (3) a plume model without the alteration effect; and (4) a plume model with the alteration effect.
The presence of CO2 in the reservoir layers can be detected by direct comparison and interpretation of plane-wave synthetic seismic sections, and is clearly observed when one displays the difference between the baseline and post-CO2 injection synthetics. The normalized root-mean-square imaging techniques also clearly highlight the time-lapse differences between the baseline and post-injection seismic data.
The laboratory-conducted alteration of the petrophysical properties of the reservoir had a strong influence on the reflected signals in the seismic sections. The greatest difference was revealed on seismic sections with 1% CO2 saturation, increasing the detectability of the stored CO2. The difference decreased with an increase in CO2 content.
The saturation of CO2 could be qualitatively estimated up to a value of 5%. Higher saturation produced a strong signal in the repeatability metrics but the seismic velocity varied so slightly with the increasing gas content that the estimation was challenging. A time shift or push-down of the reflectors below the CO2 storage area was observed for all scenarios.
According to changes in the amplitude and two-way travel times in the presence of CO2, reflection seismics could detect CO2 injected into the deep aquifer formations even with low CO2 saturation values.
Our data showed the effectiveness of the implemented time-lapse rock physics and seismic methods in the monitoring of the CO2 plume evolution and migration in the E6 offshore oil-bearing structure. The new results obtained could be applied to other prospective structures in the Baltic region.
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Reservoir characterization using electrofacies analysis in the sandstone reservoir of the Norne Field (offshore Norway)
Authors Gil G. Correia and Denis J. SchiozerThe Norne Field reservoir sandstone comprises Early–Middle Jurassic interbedded sandstones and shales to massive sandstones with some thin continuous cemented interlayers. A detailed characterization of the geological heterogeneities through electrofacies analysis, together with the simulation grid refinement, has been used to derive representative facies and petrophysical models (porosity, net-to-gross (NtG) and permeability).
An electrofacies database was created comprising six rock types, ranging from cemented carbonates through shales and into clean sandstones. In the absence of available cored sections, the electrofacies scheme was validated by the geological and petrophysical reports of 26 wells using gamma-ray, neutron and density logs. An artificial neural network algorithm enabled the probabilistic discrimination of the different types of electrofacies, with a sampling rate of 0.125 m. This high-resolution electrofacies database, together with a high-resolution geomodel grid, enabled us to map the fine-scale heterogeneities mainly materialized by decimetre shales and cemented layers that could represent stratigraphic barriers to vertical fluid displacement.
The high-resolution datasets created in this study will form the working basis on which to perform a probabilistic and multi-objective history matching guided by production and 4D seismic data, and assisted by geostatistical parameterization techniques.
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A workflow for vertical and horizontal near-wellbore permeability modelling in the McMurray Formation
Authors O. Babak and J. ResnickThe McMurray Formation is the most volumetrically important source of bitumen in the Canadian oil sands. While there are many parameters that affect prediction of bitumen recovery in commercial in situ oil sand projects, absolute permeability is the most important geological parameter. In this paper, we describe a customized near-wellbore modelling workflow for the estimation of vertical and horizontal permeability in the McMurray Formation using high-resolution microresistivity images. All steps required to calculate permeability logs calibrated to core plug measurements are documented and detailed. To show a general applicability of the method, a case study of several wells from the Cenovus Energy Inc. (Cenovus) Foster Creek project is presented. The wells are specifically selected to be different in terms of facies, their characteristics and interval lengths.
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A measure of facies mixing in data upscaling to account for information loss in the estimation of petrophysical variables
Authors Saina Lajevardi and Clayton V. DeutschBlocking facies information to a constant length prior to three-dimensional (3D) modelling is necessary with current 3D geostatistical modelling techniques. The high-resolution information from core and well logging must be upscaled to unify the scale to a target scale considered in building the 3D numerical models. A downside is the inevitable loss of information when the majority facies is assigned to each upscaled interval. The loss of such information could become problematic when dealing with small shale barriers in the middle of the reservoir or at the boundary of the facies transitions. This paper addresses the information loss by retaining as much information as possible in the upscaling process and proposes a metric to account for small-scale information that is mixed during the process: such a metric is referred to as facies mixing measure (FMM). Retaining more information in the upscaling process and utilizing that information to better model petrophysical properties is an important contribution. FMM is calculated during the upscaling step and is treated as a secondary property during petrophysical property modelling. Cross-validation with two different datasets demonstrates improvements in porosity estimation.
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Investigation of CO2 storage in a saline formation with an angular unconformity at the caprock interface
Authors Seyed M. Shariatipour, Gillian E. Pickup and Eric J. MackayStudies of oil reservoirs show that unconformities may occur between the reservoir and the caprock. At the boundary where the unconformity occurs, there may be a layer of higher permeability compared to the caprock. Such traps may occur at CO2 storage sites and, therefore, their effect should be investigated. In this work, we simulate CO2 storage beneath angular unconformities, where sandstone layers have been tilted and eroded prior to the deposition of a caprock. After preliminary studies into the effect of gridding such traps, we describe simulations of a range of 2D and 3D models. The results reveal that migration of CO2 is influenced by the lithology beneath the unconformity, which could have been modified by weathering or diagenesis. This can have both positive and negative effects on the CO2 storage capacity and security. It shows that an unconformity model that has a layer of high permeability at the interface between the aquifer and the caprock, as a result of weathering or diagenesis, can contribute to pressure diffusion across the reservoir. This could improve CO2 sequestration by providing pathways for CO2 migration to access other parts of the storage complex. However, this could also have a negative effect on the security of CO2 storage by providing pathways for CO2 to migrate out of the storage formation and so increase the risk of CO2 leakage.
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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)