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- Volume 40, Issue 3, 2022
First Break - Volume 40, Issue 3, 2022
Volume 40, Issue 3, 2022
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Some Improvements in Intensely Faulted Geological Setting Interpretation by a Multi-Scale Approach
Authors D. Krilov and M. KrylovaAbstractSubsurface deformed zones and their characteristics have a substantial influence on the distribution of oil and gas reserves as well as on production. The use of seismic data for delineating structural compartments and for modelling fault blocks in a region subjected to intense, multiphase tectonic events can be a very difficult and non-unique task as multiple interpretive solutions are possible. Generally, authors describe and substantiate the modelling technology workflow based on complex multiscale averaging of horizontal seismic slices. In this paper our discussion is restricted to the specific case of intense multiphase and multidirectional deformations and routinely processed seismic data. Instead of fault systems that appear to follow trends matching regional tectonic styles, the elementary fault planes interpreted from seismic data sometimes look chaotic. To increase the reliability of seismic interpretation and derive reasonable geological models, modification of an effective fault modeling technique is introduced. It employs a multiscale, integrated geologic approach along with seismic effective modelling basics, i.e. comprising initial noise and data spectrum considerations, model simplification and adjustment to the interpretive setting. An effective fault model includes effective faults – linear approximations of unambiguous fault planes as well as groups of ‘scattered’ elementary planes. Effective faults are used to delineate different zones of comparable rock breaking deformation. These are characterized by an areal distribution of fault planes seen on stratal seismic slices. An approximation is made using specially processed seismic attribute stratal slices, which could be referred to as seismic multiscale fracturing images. The processing algorithms include smoothing, smart averaging, and coherent filtration. Piecewise, discontinuous values of raw seismic fracturing after smoothing provide an additional opportunity to delineate deformed zones and also to upgrade the geological model based on production data.
The Chayandinskoye Field in East Siberia was chosen to demonstrate the effective fault modelling technique on an intensely faulted geological setting.
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Digitising Svalbard’s Geology: the Festningen Digital Outcrop Model
AbstractThe renowned Festningen section in the outer part of Isfjorden, western Spitsbergen, offers a c. 7 km-long nearly continuous stratigraphic section of Lower Carboniferous to Cenozoic strata, spanning nearly 300 million years of geological history. Tectonic deformation associated with the Paleogene West-Spitsbergen-Fold-and-Thrust belt tilted the strata to near-vertical, allowing easy access to the section along the shoreline. The Festningen section is a regionally important stratigraphic reference profile, and thus a key locality for any geologist visiting Svalbard. The lithology variations, dinosaur footprints, and the many fossil groups, record more than 300 million years of continental drift, climate change, and sea level variations. In addition, the Festningen section is the only natural geoscientific monument protected by law (i.e. geotope) in Svalbard. In this contribution, we present a digital outcrop model (DOM) of the Festningen section processed from 3762 drone photographs. The resulting high-resolution model offers detail down to 7.01 mm, covers an area of 0.8 km2 and can be freely accessed via the Svalbox database. Through Svalbox, we also put the Festningen model in a regional geological context by comparing it to nearby offshore seismic, exploration boreholes penetrating the same stratigraphy and publications on the deep-time paleoclimate trends recorded at Festningen.
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Reservoir Monitoring by Inversion of Reservoir Pressure and Saturation Changes from Time-Lapse Avo Differences and Time-Shifts
Authors Stefan Carpentier, Boris Boullenger and Eduardo BarrosAbstractThe main storage-related challenges for accelerated deployment of CCS are capacity, confidence and cost. These challenges are to be addressed by focusing on improving strategies for monitoring and management of the pore pressure distribution in the CO2 storage reservoir. Pressure-driven decision support protocols are to be developed for safe and cost-effective reservoir monitoring. These protocols will enable the operator to maximize CO2 storage capacity and quickly turn monitoring data indicating non-conformance into plans for corrective actions. A new extended method is developed for inverting and de-noising reservoir pressure and water saturation changes from time-lapse AVO differences and time-shifts for the purpose of CCS monitoring and conformance. Detailed reservoir pressure and saturation fronts are obtained for seismic timelapse data in the Norwegian offshore, honouring reservoir compartments and fault boundaries found in comparative studies. Applications on CCS and non-CCS fields offshore Norway were researched in synthetic and field data cases for purposes of benchmarking, pre-storage analysis, monitoring plans and conformance studies. Back-estimations of pressure and saturation changes were successful for both synthetic and field data and have made this method substantially more credible for field cases and seismic history matching.
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Accurate Measurements of Seabed Subsidence Above Norwegian Gas Fields
Authors Ola Eiken, Torkjell Stenvold and Håvard AlnesSummaryField-wide seafloor subsidence has been monitored at ten hydrocarbon fields offshore Norway. Subsidence provides lateral information on compressibility and pressure depletion in the reservoirs. This has been used to calibrate geomechanical and reservoir flow models, to map reservoir and aquifer compaction and identify poorly drained compartments. Water pressure measurements have given survey-internal precision of 2–5 mm. Tidal variations in the seafloor pressure have been carefully measured and corrected, which requires a spatial grid of reference sensors. A segment of the Midgard gas field showed significantly less subsidence than expected. This was interpreted as being caused by less depletion. A new well was drilled based on the subsidence data, a reinterpretation of the structural model, and a revised flow model. Almost virgin pressure was found. The well has since been the best producer on the field and paid back the cost of data acquisition by at least two orders of magnitude.
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Connecting Elastic Properties Estimated from Seismic Inversion to Reservoir Properties and Geologic Interpretations
More LessAbstractThe need to connect elastic properties recovered from seismic inversion to reservoir properties and geologic interpretations creates an opportunity to define acoustic impedance and related elastic properties in a way that lends them petrophysical and geologic relevance and character. Starting with established response relations for reciprocal velocity and bulk density, I present novel petrophysical interrelations of P-wave and S-wave impedance that satisfy the following criteria: (1) P-wave impedance is linearly related with P-wave velocity (Vp). (2) S-wave impedance is linearly related with S-wave velocity (Vs). (3) P-wave impedance is linearly related with Vp/Vs ratio. (4) The slope and intercept terms of these linear relationships consist of coefficients dependent on lithology or rock-type, effective stress, grain contact areas, and the pore fluid. (5) These interrelations and response equations for reciprocal velocity and bulk density are rock-typing criteria. I also show practical examples that prove the linearity predicted, as well as values of slopes and intercepts of the linear relationships that uniquely discriminate clastic and carbonate reservoirs. The results achieved so far lead to a new knowledge base in mathematical petrophysics for systematic development and use of equations relating products of seismic inversion, as well as widening the spectrum of combined and simultaneous applications of P-wave and S-wave data.
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Monitoring the Snøhvit Gas Field Using Seabed Gravimetry and Subsidence
Authors Hugo Ruiz, Martha Lien, Martin Vatshelle, Håvard Alnes, Marco Haverl and Henrietta SørensenAbstractGravimetry and subsidence surveys are regularly conducted to monitor the gas-producing Snøhvit field. This technology provides insight into reservoir dynamics with lower costs and shorter turn-around time than widespread 4D seismic data. Through two decades, improvements in survey procedures and instrumentation have led to significantly better sensitivity to both gravity changes and subsidence. This has resulted in improved sensitivity to mass changes and compaction throughout the reservoir. In this article, we analyse the evolution of the noise level in the three surveys at Snøhvit in 2007, 2011 and 2019. We present in detail the results for the 2011–2019 time-lapse, and we describe how these measurements are incorporated into the history-matching routines and used to reduce the uncertainty in key reservoir parameters.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)