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- Volume 3, Issue 10, 1985
First Break - Volume 3, Issue 10, 1985
Volume 3, Issue 10, 1985
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Shoot between the group for simulated multichannel processing flexibility
By M.R. HobsonWhere standard recording techniques are used it is not uncommon for seismic reflection data to contain undesirable, spatially aliased energy. For conventional recording layouts, the receiver station spacing controls the spatial sampling density so that higher wavenumber definition requires smaller spacing. Selection of the receiver station spacing with a limited number of recording channels is governed by the minimum and maximum offsets required to sample adequately both near-surface and deeper horizons. All too often the shallower reflections, which contain a larger proportion of the shorter wavelengths, are inadequately spatially sampled. But if a relatively small station spacing is chosen then there is insufficient differential moveout for the suppression of multiples by common mid-point stacking. However, if the number of channels is limited, it is still possible to increase the spatial bandwidth by simulating the recording of any integer multiple of the number of channels actually available. The method is appropriate for the acquisition of land data using surface sources because it involves the recording of more than one conventional record on each receiver spread from source positions spaced at equal intervals over one receiver station interval. The individual records for each receiver spread can be interleaved to simulate one field record on a multiple number of channels. This acquisition technique is not a new concept and has been utilised in several countries. However, the full processing potential has not yet been fully realised. In this paper the main recording and pre-stack processing concepts are demonstrated by a series of examples showing data in the time-distance and frequency wavenumber (f-k) domains. A real data set allows comparisons to be made between different processing sequences using this flexible recording method.
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Seismic reflection surveying offshore Durham, England - a carbonate problem area
Authors F. Jifon and N.R. GoultyThe importance of mapping geological structure by seismic profiling before planning the layout of a coal mine has been discussed by Ziolkowski (1979). While boreholes are essential for the identification of lithology, the measurement of seam thicknesses and the recovery of coal samples by coring, they cannot locate faults except where a fault happens to intersect a borehole, and it is primarily the pattern of faulting which determines the optimum layout of modern coal mines using longwall extraction. Obtaining good seismic data from coal sequences offshore Durham has been and continues to be a problem. The National Coal Board provided the data sets used in this study with a view to seeking improvement. The Northumberland and Durham coalfield in northern England extends offshore, and workings from coastal colleries already reach out under the North Sea to distances of 10 km from the coast. The cost of each exploration borehole offshore is around ft million, even at the relatively shallow depths of interest for coal mining (less than 700 m in this area). In order to plan further extensions to the mine workings without enormous exploration costs, it is highly desirabie that good seismic reflection data are obtained for interpretation of the geological structure between boreholes. In 1979 the National Coal Board carried out a seismic survey over a grid of lines spaced 1 km apart covering more than 400 km2 of the offshore extension to the coalfield. To the north, offshore Northumberland, the Coal Measures of Upper Carboniferous age are only overlain by Quatemary boulder clay, and the seismic data were reasonably good. Offshore Durham the regional dip is down to the south-east, and the Coal Measures are overlain by Permian strata composed largely of the Magnesian Limestone formations which contain interbedded anhydrite bands. There is some Permian marl above the limestones and then Quarternary boulder clay up to the sea bed. In this area the data did not show much reflected energy from the Coal Measures strata. We tried to make the best of the data with some experimental processing of one of the more promising lines, but concluded with the aid of processing trials of synthetic data that the best hope for improvement lay in the acquisition parameters. Later acquisition trials were carried out on the same line in 1982 and 1984, but did not show any improvement over the 1979 data as far as the interpretability of Coal Measures structure was concerned. The question which now needs to be answered is whether better, more interpretable seismic reflection data can be obtained with presently available techniques, so that management can be advised on future exploration and planning strategy. We conclude that there is still room for improvement in the seismic source, which should be used with an appropriate streamer configuration, but we are not optimistic that dramatic improvement in data quality can be made in this problem area because of the seismic transmission characteristics of the Permian strata.
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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)