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- Volume 34, Issue 1, 2016
First Break - Volume 34, Issue 1, 2016
Volume 34, Issue 1, 2016
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Seismic spectral decomposition and inversion for buried channels delineation: a case study from the Asmari Reservoir, southwestern Iran
Authors Ahmad Ashtari and Ali ArzaniDense data sampling in 3D seismic surveys provides a clear image from subsurface layers, but it may fail in the cases where the thickness of a layer is below seismic resolution (e.g. thin beds and channels). Seismic spectral decomposition and inversion are among methods that can help us to delineate and study the sub-seismic resolution features. This paper shows how the buried channels of the Asmari formation in an oil field located in southwest Iran were delineated and are studied using seismic spectral decomposition and inversion. The Gabor wavelet transform was used to divide seismic frequency spectra into eight bands out of which three frequency bands with central frequencies of 24, 29, and 35 Hz have been selected for RGB blending for its perfectness in exposing the channels. Several distinct channels were detected at 15ms interval below the top of the Asmari formation. The P-impedance data coincide with the findings further giving information on lithological aspects. Detailed delineation of the channels became possible by using the Matching Pursuit Decomposition (MPD) method. In order to delineate sub-seismic resolution features, spectral decomposition is used to transform time-domain seismic data into the frequency domain and then the special elements corresponding to these subsurface features are enhanced with spectral blending.
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The effect of location error on microseismic mechanism estimation: synthetic and real field data examples
Authors Michael Kratz and Michael ThorntonThe decomposing of the full moment tensor of micro¬seismic events observed during hydraulic fracture stimulations into double couple (%DC), compen¬sated linear vector dipole (%CLVD), and isotropic (%ISO) components has been shown to be useful for making more complete characterizations of these events (Williams-Stroud, 2008). While this information about the nature and geometry of a fracture is important and very telling, any source of potential error in these decomposi¬tions must be taken into account. One source of particular importance to microseismic monitoring is the effect of loca¬tion error on the full moment decomposition. With this type of analysis becoming more prevalent, there is concern as to whether the effect of location error on potential interpreta¬tions and recommendations based on microseismic fracture geometry is thoroughly understood. Moment tensor inversion of microseismic data is an immensely powerful interpretation tool. An understanding of the nature of the rock failure supports the development of discrete fracture networks (DFN), reservoir simulation models, and stimulated reservoir volume estimates. Such interpretations are a large part of the driving force behind the growth in microseismic monitoring. Furthermore, a proper characterization of the event mechanism is necessary in full waveform imaging of microseismic data to properly account for the radiation pattern of the signals (Duncan, 2010).
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Vibroseis evolution: May the ground force be with you
Authors Spencer Rowse and Anthony TinkleAlthough the precision of positioning and fidelity of recording of the sensors in land seismic exploration has increased significantly over the last three decades, the same cannot be said about the accuracy in the determination of the time varying signal generated from land seismic sources. At best, the current methods of deter¬mining the source signature from vibrator sources used on land are approximate. A selective examination of representative past and present models and concepts in the modelling of the source/earth interactions suggests that current trends in land seismic acquisition (towards point source, point receiver surveying, increased emphasis on seismic attributes, and the use of distributed simultaneous and overlapping source events) are forcing a renewed focus on more accurate measurement and/or prediction of land seismic source signatures. New models are required that better describe the dynamically interactive nature of the source-earth relationship. ‘All models are wrong, but some are useful’. This aphorism by the statistician Box (Box and Draper, 1987) is meant to emphasize that any mechanistic model should have the following advantages: It contributes to our scientific understanding of the phenomenon under study. It usually provides a better basis for extrapolation (at least to conditions worthy of further experimental investigation if not through the entire range of all input variables). It tends to be parsimonious in the use of parameters and to provide better estimates of the response Paraphrasing the above, the most that can be expected from any model is that it can supply a useful approximation to reality. From this, a pragmatic geophysicist (some would say a cynical one) might ask how wrong do models have to be in order not to be useful.
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Extending the useable bandwidth of seismic data with tensor-guided, frequency-dependent filtering
Authors Edward Jenner, Lisa Sanford, Hans Ecke and Bruce GolobImproving the bandwidth of seismic data has been an ongoing endeavour in increasing the usability of seismic data in many plays throughout the world. While various broadband acquisition techniques have been recently developed for marine acquisition, the most significant issue for land seismic has been the low signal-to-noise ratio, particularly at the low and high ends of the frequency spectrum. In this paper, we describe a frequency-dependent filtering technique that can significantly increase the available bandwidth of the seismic data. We show a field data example and demonstrate that the enhanced bandwidth seismic data ties with well logs in the area. A variety of methods have been proposed to increase the bandwidth of seismic data that fall broadly into three categories: 1. Inversion-type approaches where some pre-determined information or assumption is used to overcome the inherent non-uniqueness of the inversion solution (Zhang and Castangna, 2011). 2. Methods that use the available bandwidth with high signal-to-noise to extrapolate or ‘predict’ the low and high-frequency components (Smith et al., 2008). 3. Methods that apply some sort of frequency-dependent filtering to the seismic data to improve the signal-to-noise of the high and/or low-frequency components (Whitcome and Hodgson, 2007).
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Some geotechnical considerations for subsea decommissioning
By Andy SmallWhilst decommissioning of offshore oil and gas infrastructure has been taking place in the North Sea since the early 1990s, a significant number of topside and subsea structures, pipe¬lines, umbilicals and cables are scheduled to be decommissioned between now and 2040. As such, decommissioning activities will represent an increasingly substantial proportion of offshore operations and associated engineering. According to a recent survey by Oil & Gas UK, nearly £17bn is forecast to be spent on scrapping 79 North Sea platforms and plugging 1200 wells over the next ten years. The latest forecast is up from a total of £14.6bn recorded in 2014. This represents around one-sixth of the 470 installations that will require decommissioning over the next 30 to 40 years. The removal of subsea and top¬side infrastructure presents a significant challenge to operators, especially infrastructure installed prior to the 1992/1998 OSPAR agreements, where full decommissioning may not have been explicitly considered during the original design phase. Most offshore infrastructure is bespoke, designed for the specific requirements of the produc-tion philosophy, marine environment setting, with the available technology and best practice of the day. Each decommissioning project will present challenges to the operators and the contractors tasked with removal of the infrastructure. The greatest decommissioning costs are associated with the removal of large fixed concrete and steel installations. However, given the large population of subsea equipment and pipelines to be decommissioned, a significant proportion of the £30bn to £40bn estimates required to decommission the UKCS will be associated with removal of subsea infrastructure. As all subsea infrastructure inter¬acts with the seabed in some manner, understanding the geotechnical aspects and managing geotechnical risk will be of significant benefit to executing decommissioning projects successfully.
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Assessing the impact of two recessions on the oil and gas industry: severity of declines and future outlook
Authors Waleska Rodrigues and Ruud WeijermarsSix years after the Great Recession of 2008/2009, the oil and gas industry is afflicted by a new crisis: OPEC’s global oil price war. Many see the 2014/2015 oil price plunge as a test of financial endurance between OPEC and US shale producers. Shale producers have added 4 million barrels of crude per day to global oil supply since 2010, and reduced the US need for Saudi imports. Canadian tar sand producers added nearly another 4 million barrels per day in less than a decade. Rising output of US shale oil and Canadian tar sand producers threatened to erode the OPEC market share. All growth in global oil demand has over the past decade led to a rise in market share only for non-OPEC producers. That is what Saudi Arabia and its OPEC associates wanted to stop. In an effort to put the new entrants (unconventional oil producers) out of business, the 2014/2015 oil price plunge has been deliberately prolonged by OPEC, which continues to oversupply the market by more than 1.5 million barrels per day. Unlike today, OPEC helped in 2008/2009 to restore oil prices rapidly by steep production cuts in response to lagging oil demand owing to the global recession. In this article, we compare the severity of the impact brought on by the two most recent oil price crises on the various types of oil companies. Tracking timely market capitalization and P/E ratios (share price per earnings) of the oil majors covering the 2008 epoch of oil price decline confirmed that oil company KPIs recovered rapidly during the second quarter of 2009 (Weijermars, 2010; 2011). An update of the analysis of key performance indicators (KPI) over the past decade provides insight into how companies are affected by poor market conditions. We examine the periods before the two recessions, and include post-2014 data after the beginning of the current oil price war. This study tracks the impact of economic downturns on 26 upstream oil and gas companies. In order to facilitate the analysis of the data for the 26 companies tracked on this study, they were split into peer groups based on shareholder structure, size of the corporation, degree of vertical integration and the types of oil/gas production most commonly performed by the company. The five different peer groups studied are majors, independents, US shale producers, Canadian oil sand producers and public private partnerships (PPP). The five peer groups and their respective companies are presented in Table 1. The KPIs chosen for our study are share prices, market capitalization and return on capital employed (ROCE). These were tracked annually, quarterly and daily between 2005 and 2014, and for the first half of 2015 with information available until completion of our study (July 2015).
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3D-3C Multicomponent Seismic – A successful fracture characterization case study in Algeria
Authors M. Donati, J.L. Piazza, A. Rollet, S. Baillon, D. Marin, V. Belz, H. Toubiana, J. Castro, A. Bouheouira and M. RahaMulti-component acquisition has been used in the industry for many years for fracture density and orientation studies with proven success. In the field under study, it has been observed from well information at target level that there is a relationship between gas production and natural fractures, faults, and changes in facies. The target horizon located at a depth of approximately 1950 m is composed of low-porosity gas-bearing Ordovician sandstones of 5 to 6% average porosity. The Ordovician is characterized by a highly heterogeneous matrix affected by natural fractures. This paper describes a 3D multi-component land seismic project conducted in Algeria, designed to perform a fracture characterization study. This pilot survey, acquired in 2010 over the Tin Fouyé Tabankort West block, is the first land 3D-3C acquisition ever performed in Algeria. It covers an area of about 67 km² centered on a well location. The following project phases will be described hereafter: (1) 3D-3C survey design and field operations, (2) Main steps of the PP and PS-wave pre-processing sequences, (3) PP and PS-wave interpretation study at deep levels made possible by the cleaned and signalpreserved seismic data. The resulting PP seismic dataset from the 3D-3C survey provides a better resolution of subtle faults and lineaments than the conventional 3D acquired in 2003 and reprocessed in 2010, even though the noise level remains slightly high. Furthermore, PS seismic data shows evidence of azimuthal anisotropy in relation to the faults and lineaments interpreted on the PP dataset. Anisotropy analysis results tie reasonably well with FMI information available in the Ordovician, showing great potential for using this technology for fracture studies.
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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)