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- Volume 20, Issue 6, 2002
First Break - Volume 20, Issue 6, 2002
Volume 20, Issue 6, 2002
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Progress report on the road to safety
By A. McBarnetGiven the lip service paid to safety in the E&P industry, it’s surprising to find that Rod Thonger is running practically the only dedicated HSE management consultancy for seismic operations worldwide. He spoke to Andrew McBarnet about the industry’s continuing attempts to improve its safety record.
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Rapid Walkaway VSP survey achieves result in Venezuela
Authors N. Brooks, S. Shaw and H. SimpsonN. Brooks, S. Shaw, and H. Simpson of CGG Borehole provide a first-hand account* of how a high-resolution intermediate walkaway VSP survey in Venezuela. The operation, with a tight deadline, provided additional information for the interpretation of faulting at reservoir level, considered essential to the drilling programme
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How integration of well log, core, borehole seismic and cross-well seismic data can offer a powerful tool in complex structural situations
Authors G. Gomez, C. Planchart, Y. Chon, A. Di Massimo, G. Gonzalez, E. Sifontes and D. OctavioThis work presents a methodology for resolving a complex structural reservoir using the acquisition and interpretation of diverse core, well log, VSP, and cross-well data. The Carito reservoir is in Eastern Basin of Venezuela, north of Monagas. The production formation is located between 13 000 and 17 000 ft in Tertiary and Cretaceous sands within the Naricual and San Antonio formations. In August 1999, two new wells were drilled in the southern part of the Carito Field. The locations of the new wells were based upon a structural model derived from existing surface seismic data. When these wells were drilled, the top of the producing formation was encountered at substantially different depths than was predicted, indicating that the structure of the area was much more complex than previously understood. We concluded that a detailed evaluation of all available data should be undertaken.
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Conical sandstone injection structures imaged by 3D seismic in the central North Sea, UK
Authors S. Molyneux, J. Cartwright and L. LonerganThe improved imaging and resolution potential of 3D seismic data has been demonstrated in many recent case studies (e.g. Weimer & Davis 1996). The improved resolution of 3D often allows the interpreter to recognize features that would not previously have been mapped using conventional 2D grids because of spatial aliasing (Clausen & Huuse 1999; Stewart 1999). In some cases this has led to the discovery of new types of deformational or sedimentary structures (e.g. Cartwright 1994; Davies et al. 1999). We consider the origin of some enigmatic amplitude anomalies recognized and mapped on a 3D seismic survey from the central North Sea. These anomalies are characterized by their conical geometry, and are localized in a specific stratigraphic unit, the Lower Eocene. Initial lithological calibrations from wells aimed at deeper targets suggest that these structures are intrusive sand sheets, with thicknesses of up to 30 m. If this interpretation is correct, these conical sand sheets would be the largest form of clastic sedimentary intrusion yet reported. The paper describes the evidence supporting this interpretation of the amplitude anomalies, reviews alternative models for their origin, and concludes with a brief discussion of the wider importance of this interpretation for hydrocarbon exploitation in deepwater sandstone reservoirs.
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Application of pre-stack wave equation datuming to remove interface scattering in sub-basalt imaging*
Authors F. Martini and C.J. BeanIn recent years sub-basalt imaging has been a problem of general interest in the petroleum industry. Sub-basalt images are often known to be of very poor quality. Conventional reflection seismic methods are usually not very successful at imaging either the internal flow structure of the basalt or the sub-basalt structures. The ability to image at depth is critically dependent on transmitting enough energy to the target. The matter has often been related to high velocity in the basalt layers, which yields high impedance contrast and a subsequent limited penetration of the P waves. It has recently been seen that this is not the major controlling factor in the imaging problem. First of all, basalts very often do not have such a high velocity, and even when they do, sufficient seismic energy is usually transmitted and propagates through basalt (e.g. O’Doherty & Bean 1999; Planke & Eldholm 1999). Here we show that the imaging problem is due to a combination of factors, amongst which the internal and interface structures of flood basalt play an important role. Both the heterogeneous nature of basalt interfaces and its internal structure strongly affect sub-basalt seismic imagery. The role of wave scattering in seismic imagery is well documented in the literature (Gibson & Levander 1988; Pullammanappallil et al. 1997; Martini et al. 2001) as well as the effects of irregular interfaces on wave propagation (Paul & Campillo 1988; Purnell et al. 1990; Hestholm & Ruud 2000; Ruud & Hestholm 2000). Lava cake geometry, intra-lava velocity variations and inter-layering between lava and sediments create a very heterogeneous structure that attenuates, scatters and multiply reflects the energy transmitted into the layers. Some of these mechanisms have been evoked, either separately or together, to account for poor sub-basalt imagery. In heterogeneous media, scattering occurs as a result of the interactions of seismic waves with spatial variations in the material properties of the medium, variations that range in size from several seismic wavelengths to a small fraction of the wavelength. The scattering regime depends upon the relationship between the propagating wavelength and the scale of the heterogeneity. Scattering by heterogeneities affects a number of seismic observables, including amplitudes, traveltimes, spectra and waveforms. Another important consideration is the ratio between the thickness of the heterogeneous layer and the wavelength propagating through it. To facilitate the generation of a significant amount of body wave scattering, the layer has to be thick enough to enable the propagation of a few cycles through it, notwithstanding the fact that high frequencies are preferentially scattered (Leary 1995). This reasoning may go some way toward explaining the conclusions that many authors have reached that low frequencies are better than high frequencies in sub-basalt exploration. With low frequencies (long wavelengths) less cycles travel into the heterogeneous layers, and the long wavelengths miss the small scale variations in the media. Therefore, the wavefield is less scattered. We emphasize the importance of this factor as scattered waves can seriously contaminate lower structures. Scattering in highly heterogeneous layers ensures that waves continue to be recorded at time and depths corresponding to lower layers, which are then not properly imaged due to this contamination. The degree of this contamination is controlled by the ‘size’ of heterogeneity in the layer, and the wavelength propagating through it. For ‘thick’ layers, where internal body wave scattering is a major cause of image contamination, migration and velocity control have been shown to be of extreme importance (Martini et al. 2001). Basalt boundary surfaces are not expected to be smooth but to contain roughness at a range of scales, including the seismic wavelength. Again, the scale of corrugations with respect to incident wavelength is the important factor. Irregular interfaces have a disruptive effect on wave propagation. So, both internal and interface scattering contribute substantially to the problem, one or the other being the dominant factor according to a balance between different parameters, such as basalt layer thickness, nature of the interfaces and seismic wavelength. Numerical investigations indicate that interface scattering dominates over body scattering in the sub-basalt imaging problem (Martini & Bean, in press). In this work we concentrate on the interface aspect. As a possible solution to the detrimental effect that interface scattering can have on deeper reflector imaging and continuity, a wave equation based pre-stack datuming has been tested, both on synthetic and real field data.
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Industry Feature: A new technology of reservoir stimulation through exposure to weak seismic waves
More LessIncreasing oil production and its rate of recovery from existing reservoirs is perhaps the main priority of the oil industry worldwide. In this article Oleg V. Dobronravov, director of Seismotechglobe, based in the Netherlands, describes the work of his company in the development of a novel technology originating from Russia. Versions of this presentation have been given at the Technical University of Delft and at the EAGE Research Workshop on Reservoir Rocks held last year in Pau, France.
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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)