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- Volume 22, Issue 7, 2004
First Break - Volume 22, Issue 7, 2004
Volume 22, Issue 7, 2004
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The mistake of Descartes
More LessPaolo Dell’Aversana, R&D technical leader, Eni Exploration and Production Division, takes issue with Prof Peter Hubral’s thesis in his article ‘Pythagoras and the mystic Orient’ published in the May 2004 issue of First Break. We also publish Prof Hubral response. Critical thinking about geoscience should be a primary activity in our scientific community. Prof Peter Hubral is the living demonstration that excellent geophysical competence is possible without forgetting other fundamentals about our work and life. His article ‘Pythagoras and the mystic Orient’ (First Break, May 2004), is very interesting from this perspective. It represents a new kind of input for geophysicists completely different from any traditional paper that has appeared in the journal. In the recent past I wrote a couple of short notes (First Break, 2002a, 2002b) in response to the article by Prof Hubral on creativity (2001). Once again I feel an irresistible impulse to express my point of view about the subject treated by Hubral in his new article. In particular, I was impressed by the concept of ‘an inner struggle between the mind dedicated to gaining knowledge and the soul required to gain wisdom’. If I understood correctly, this concept stands as the critical point of the article. Another couple of strong statements by Hubral are that 1) ‘The mind and the soul appear to have a tendency to separate each other…’, and 2) ‘the mind is the spiritual part in us, which is engaged with the outside world and the soul is that part related to our inner self.’ In my opinion, this ‘philosophical’ approach represents the background to a dangerous misunderstanding typical of occidental thinking, namely dualism.
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Lab manual provides students with practical guide to seismic processing
By R.A. YoungThe latest EAGE publication - A Lab Manual of Seismic Reflection Processing by Roger A. Young, associate professor, School of Geology and Geophysics, University of Oklahoma - is a new teaching tool for university level geophysics students being launched at EAGE Paris 2004. Designed to be a practical, computer-oriented guide, the manual has been produced in close association with software development company Parallel Geoscience Corporation. Here, Prof Young introduces some of the thinking behind the project. The purpose of the Lab Manual is to serve as an extension to an introductory college-level lecture course on seismic reflection processing. In my experience, the theory from such a course is much better appreciated by students after they have had an opportunity themselves to apply seismic processing to a high-quality data set. As an instructor of upper-division university undergraduates, I have found that hands-on processing exercises expand the students’ understanding of the consequences of model simplifications and mathematical assumptions imposed on the real earth in order to make it more tractable. The material in the Lab Manual is designed to take up approximately 12 afternoon lab sessions, supplemented by brief introductions to each processing topic, the references to software documentation, and to subject references. It is intended to be a self-contained package suitable for individual use or for group use in a supervised lab setting. The data provided with the Lab Manual comes from a segment of a near-surface line shot for engineering purposes by the Geological Survey of Canada (GSC), and I am grateful to Sue Pullan of the GSC for making a portion of the Casselman survey, Line 1, available and for providing an explanation of the geological objective of the survey. The data is characterized by a high signal/noise ratio, reflection frequencies up to 350 Hz, short records, and low fold. Because it contains multiples, statics variation, and diffractions, proper processing makes an obvious improvement in image quality. It is a suitable analogue for much larger energy industry surveys. A feature of the Lab Manual is the use of the Seismic Processing Workshop (SPW) software of Parallel Geoscience Corporation. Because the flow for each SPW processing stage takes less than two minutes’ execution time on a 200 MHz PC, the dataset is ideal for either self-instruction or interactive teaching. The software package allows students to process the near-surface, 2D, reflection dataset from Canada. The processing objective is to obtain optimal vertical resolution of shallow stratigraphy overlying a bedrock reflector at a depth of approximately 50 m. The data was shot for geotechnical engineering reasons, but its wide bandwidth (600 Hz), high S/N ratio, and the presence of diffractions, multiples, and a number of strong reflections make it an ideal analogue for processing seismic profiles over shallow oil and gas targets, too.
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Practicalities, pitfalls and new developments in airborne magnetic gradiometry
By S. HoggScott Hogg, whose company Scott Hogg & Associates, based in Toronto, Canada offers services to the exploration and airborne geophysical industry, reviews the latest refinements in the revitalised use of airborne magnetic gradiometers for the mining industry. The oil and gas exploration industry spurred the development of the first airborne magnetic gradiometers. The motivation was to use Euler’s equation with measured vertical gradient to calculate depth to magnetic source. Aeroservice introduced both a helicopter system and a fixed wing towed bird system in the 1960s. Interest in the Euler theory for magnetic analysis was rekindled in the mining industry 20 years later and continues to be the foundation of many new interpretation methods. In Canada, the GSC developed a vertical magnetic gradiometer in the 1970s. A national mapping programme began in the early 1980s and in response Canadian airborne survey contractors created a variety of fixed-wing and helicopter systems. The mining sector’s interest in airborne gradient measurement was based primarily on the increased spatial resolution and detail: small anomalies on the flanks of large features could be clearly resolved. Calculated vertical gradient maps, produced by simple filtering of total field, were found to provide almost the same benefit as measured gradient, at less cost, and the commercial interest in measured vertical gradient faded. Geometrics introduced a horizontal gradiometer in 1983. This development was of particular significance since, at the same time, they incorporated a technique developed by Nabighian and Hansen to derive a pseudo total field residual from measured horizontal gradients. The demise of the Geometric survey division took horizontal gradients off the horizon for a while. A decade later, this same concept was used by Nelson of the NRC, and more recently implemented in a variety of forms by De Beers and others. Geodass in Botswana, now Fugro, introduced the first 3- axis gradiometer in the early 1990s. In conjunction with the gradient measurements it provided a variety of compilation and mapping services that made use of the information. In Canada, Terraquest was the first to provide horizontal gradient measurement and Goldak the first to provide a full 3-axis fixed-wing gradiometer. At present, almost all of the airborne contractors offer horizontal gradient systems, and several can now provide full 3-axis configurations for simultaneous vertical and horizontal gradient measurement. Considerable interest in magnetic gradient measurement has arisen over the past few years. Some of the benefits of gradient are well founded and some are overstated and many are poorly understood. Magnetic gradient measurements can be used to advantage in interpretation. Vertical gradient maps, analytic signal maps, and a host of Euler based methods all use gradient information. The gradient information for these purposes may be calculated or measured. This review addresses methods that rely specifically on measured, not calculated, gradient. At present there are three such primary applications. The first is the potential to avoid diurnal interference, the second is to correct total field for variations in aircraft altitude, and the third is to make significant improvements in the accuracy and resolution of magnetic maps.
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Gold - challenging fundamentalism
By K. NaqviIn the mining for gold, like oil and gas exploration, technology considerations take second place to market considerations, and the news is not especially positive. Kamal Naqvi, precious metals analyst, commodities research, Barclays Capital Research, lays bare the economic and investment factors that are denting any high hopes for gold mining prospects. Watching markets and media commentary on the gold market in recent months, one could be forgiven for assuming that gold was simply a derivative of the Euro – such has been the correlation between the two. As a result of this close relationship, we sense a high degree of complacency throughout the industry about both the level of gold prices and the remaining structural challenges still facing the gold market. Contributing greatly to this complacency has been growing noise from the ‘bulls’ on major gold market specific schemes for why gold is still in the early stage of a major bull run. The five pillars of this ‘gold fundamentalism’ are as follows: 1. Gold prices will always trend higher. 2. Demand will surge, thanks to China (on top of India). 3. Supply is falling. 4. Central Banks will become ‘believers’ again. 5. Long-term investors will return to gold. We believe that many of these supposedly ‘bullish’ themes for the gold market are overdone, unproven or wrong. This does not mean that we will see a collapse in gold prices back below $300. However, it recognises that a consensus economic view (i.e. of robust global growth) is likely to see gold prices come under increasing pressure. For gold producers this is likely to mean that relative share price performance will increasingly reflect corporate performance rather than merely market perceptions of leverage to the gold price.
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MicrOBS: A new generation of ocean bottom seismometer
Authors Y. Auffret, P. Pelleau, F. Klingelhoefer, L. Geli, J. Crozon, J.Y. Lin and J.-C. SibuetA new generation of ocean bottom seismometers (OBS) has been developed by Ifremer (French Research Institute for Exploitation of the Sea). For the first time, the acquisition and release electronics have been integrated to decrease the size, weight and cost of the equipment. Downloading of data by USB cable and recharging of batteries is accomplished from the outside allowing redeployment of the equipment without opening the glass sphere. During an oceanographic cruise in the Okinawa Trough, off Taiwan, the equipment was successfully tested together with the older generation OBS in Ifremer. Results from the deployments of the first prototype are described here.
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Prospect hunting below Deccan basalt: imaging challenges and solutions
More LessThick Mesozoic sediments under the basalt cover of the Deccan traps along the northwest coast of India are considered to be potential targets for hydrocarbon exploration together with the Indus basin of Pakistan. Sub-basalt seismic imaging is difficult in these formations, as the Deccan traps are composed of multilayered lava flows. Seismic imaging issues associated with high velocity basalt include: 1. Multiples generated in interbedded units of basalt and between the top of the basalt and the sea floor. 2. Energy scattering from and absorption by heterogeneities. 3. Wave mode conversion at the top of the basalt. Radon-based analysis can solve some of the difficulties related to multiples. The use of low frequency sources and multicomponent technology are other methods commonly suggested to improve sub-basalt imaging. The Deccan basalt area is very heterogeneous and has not been mapped effectively by high resolution seismic. At present, only standard streamer data are available in this area. Model-based imaging together with other methods can improve the sub-basalt image and add confidence in the reservoir modelling. Imaging challenges in this setting are discussed using examples from the Kutch basin on the northwest coast of India, where the primary reservoir (Bhuj formation) is overlain by thick basalt.
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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)