Seismic Land Research Articles

Seismic Crew Survey

PreviousNext You have accessThe Leading EdgeVolume 12, Issue 11Seismic Crew Surveyhttps://doi.org/10.1190/tle12111135.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail The number of seismic land crews and marine vessels searching for oil and gas in the US and US waters increased slightly during September. The land crew total remained stable at 66, and the marine crew total increased by two to 18, for a total of 84. The September total represents a 2% increase over last month, an 11% increase over September 92, a 14% decrease from September 91, a 33% decrease from September 90, a 39% decrease from September 89, a 54% decrease from September 88, and a 56% decrease from September 87. During September, one contractor was operating one of the 63 land crews and one of the 17 marine vessels on a speculative basis.FiguresReferencesRelatedDetails Volume 12Issue 11Nov 1993Pages: 1062-1139ISSN (print):1070-485X ISSN (online):1938-3789 publication data© 1993 © 1993 by The Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished Online: 13 Jul 2017Published in print: 01 Nov 1993 CITATION INFORMATION (1993), "Seismic Crew Survey," The Leading Edge 12: 1135-1136. https://doi.org/10.1190/tle12111135.1 Plain-Language Summary PDF Download Metrics Loading ...

Seismic Crew Survey

The number of seismic land crews and marine vessels searching for oil and gas in the US and US waters decreased during July. The land crew total remained the same at 65, and the marine crew total decreased by two to 15, for a total of 80. The July total represents a 2% decrease from last month, a 16% increase over July 92, a 24% decrease from July 91, a 38% decrease from July 90, a 38% decrease from July 89, a 57% decrease from July 88, and a 56% decrease from July 87. During July, two contractors were operating one of the 62 land crews and one of the 14 marine vessels on a speculative basis.

Seismic Crew Survey

Previous You have accessThe Leading EdgeVolume 12, Issue 6Seismic Crew Surveyhttps://doi.org/10.1190/tle12060727.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail The number of seismic land crews and marine vessels searching for oil and gas in the US and US waters increased during April. The land crew total increased by eight to 63, and the marine crew total decreased by two to 14, for a total of 77. The April total represents an 8% increase over last month, a 9% decrease from April 92, a 36% decrease from April 91, a 38% decrease from April 90, a 41% decrease from April 89, a 61% decrease from April 86, and a 53% decrease from April 87. During April, one contractor was operating none of the 60 land crews and one of the 13 marine vessels on a speculative basis.FiguresReferencesRelatedDetails Volume 12Issue 6Jun 1993Pages: 678-728ISSN (print):1070-485X ISSN (online):1938-3789 publication data© 1993 © 1993 by The Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished Online: 13 Jul 2017Published in print: 01 Jun 1993 CITATION INFORMATION (1993), "Seismic Crew Survey," The Leading Edge 12: 727-728. https://doi.org/10.1190/tle12060727.1 Plain-Language Summary PDF Download Metrics Loading ...

Seismic Crew Survey

Previous You have accessThe Leading EdgeVolume 12, Issue 3Seismic Crew Surveyhttps://doi.org/10.1190/tle12030236.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail The number of seismic land crews and marine vesseis searching for oil and gas in the US and US waters increased in January. The land crew total decreased by three to 55, and the marine crew total increased by four to 17, for a total of 72. The January total represents a 1% increase over last month, a 9% decrease from January 92, a 37% decrease from January 91, a 41% decrease from January 90, a 47% decrease from January 89, a 63% decrease from January 88, and a 55% decrease from January 67. During January, three contractors were operating three of the 52 land crews and one of the 16 marine vessels on a speculative basis.FiguresReferencesRelatedDetails Volume 12Issue 3Mar 1993Pages: 161-238ISSN (print):1070-485X ISSN (online):1938-3789 publication data© 1993 © 1993 by The Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished Online: 13 Jul 2017Published in print: 01 Mar 1993 CITATION INFORMATION (1993), "Seismic Crew Survey," The Leading Edge 12: 236-238. https://doi.org/10.1190/tle12030236.1 Plain-Language Summary PDF Download Metrics Loading ...

New possibilities in controlled-source seismology with a magnetic levitation vibrator

Summary. A new-technology, broad-band seismic land source based on the principle of magnetic levitation is under development. The new source is designed to overcome limitations experienced with controlled-signal seismic sources at the present time, and to create new possibilities. In particular, the new source extends the constant peak force frequency band down to 2 Hz, and is capable of at least several weeks continuous, coherent transmission. It will enable three-dimensional long-range (>200 km) controlled-signal seismology with the potential for active earth tomography down into the mantle and systematic earthquake precursor measurement, and should improve shallow and deep seismic profiling technology. The optimum transmission frequencies depend on Q, transmission range, and noise spectrum.

L'EGALISATION SPECTRALE: UN MOYEN D'AMELIORER LA QUALITE DES DONNEES SISMIQUES*

AbstractIn land seismic surveys spectrum equalization can increase the quality of seismic data in a selected frequency band. The power of lower frequencies in the spectrum of input traces is generally greater than that of higher frequencies, particularly in land seismic surveys because of ground roll. In order to improve the quality of seismic data it is necessary to raise the energy of higher frequencies to the same level as that of lower frequencies, without alteration of the phases.The first step of the method is to compute the amplitude spectrum of each input trace to determine a weighting function which is then applied to the amplitude spectrum in order to balance it. The function is the inverse of the short wavelength variation of the amplitude spectrum. The short wavelength variation can be obtained by interpolation between average values of the modulus of the amplitude spectrum computed in narrow bands within a selected band of frequencies. Another way of obtaining the short wavelength variation is to apply a low‐pass filter to the amplitude spectrum. The calculations are readily performed in the frequency domain by the Fourier transform.Spectrum equalization is automatically adjusted to each trace and does not modify the average amplitude in the time domain. However, as the frequency band and energy of the ground roll both vary according to the distance from the shot, spectrum equalization tends to make the spectrum of output traces independent of the offset distance.The use of spectrum equalization before any two‐dimensional filtering improves ground roll elimination. Continuity and resolution of horizons are also increased by spectrum equalization before CDP stack.Several examples of applications of spectrum equalization to seismic land and marine surveys are shown.

ELECTRONIC ACCELERATION‐SENSITIVE GEOPHONE FOR SEISMIC PROSPECTING***

AbstractPreviously ignored characteristics of the seismic recording instrument are presently experienced as limitations as more sophisticated interpretive methods using wider frequency ranges are developed to extract stratigraphic information from seismic land data for hydrocarbon and mineral exploration. Most of these limitations arise from inadequate characteristics of the first element of the seismic instrument: the geophone. A geophone does not faithfully follow the motion of the earth for higher frequencies due to poor geophone‐earth coupling. This filtering effect brings about time shifts that are dependent on the frequency and the soil type. A geophone can also produce spurious outputs, brought about by the motion of the suspended part of the geophone, with a magnitude comparable to that of the desired output. The suspension is made very compliant to obtain the required sensitivity. A compliant suspension, however, gives a large sag. The geophone can therefore only be used in one position, tolerating little tilt. A compliant suspension also widens the traveling range of the movable part. Minor sensitivity changes with travel are then noticeable as nonlinearity, since the surface wave is large with respect to the reflected wave. A compliant suspension is usually realized in the form of thin, spirally shaped spring‐spiders. Such suspensions exhibit transverse or rotational resonances that are in or close to the seismic frequency band. Excited by ground roll, they can produce considerable undesirable output.The novel geophone we describe is a light‐weight (17 g) acceleration‐sensitive transducer which gives good ground coupling and partial correction for the increasing damping in the earth with increasing frequencies. It employs internal hybrid electronics for a magnetodynamic velocity‐nulling feedback system. Velocity nulling makes the movable part of the geophone virtually rigid with respect to the housing. This makes the geophone characteristics independent of the suspension. The springs used are stiff in a transverse and rotational direction so that the suspension resonances are well outside the useful frequency band. This suspension also allows the geophone to be used in any orientation while being only sensitive to the vibration component along the main axis. The feedback system makes the sensitivity flat within 1 dB from 2 Hz to 500 Hz, with a phase tolerance smaller than 5°. The geophone is robust, has no moving internal wires, employs a current output [sensitivity 1 mA/(m s−2)] and internal gain so that the signal‐to‐cable‐noise ratio is improved. This type of output allows parallel connection without any interaction between the geophones.

EFFICIENT 3‐D MIGRATION IN TWO STEPS*

AbstractThe addition of a third dimension to seismic data acquisition offers significant improvement of our reflection images of geologic structures, but potentially at a substantial increase in data processing cost. Here we study an approach to migration of three‐dimensional (3‐D) stacked data that can considerably reduce the burden of computation and data manipulation. Cascading two‐dimensional (2‐D) migrations in orthogonal lateral directions, we obtain an efficient 3‐D scheme that is exact for homogeneous media. As applied to examples of synthetic data from inhomogeneous media, the scheme introduces errors well below those attributable, in practice, to uncertainties in migration velocity. Application of this two‐step approach, using both Kirchhoff‐summation and finite‐difference algorithms, to a 3‐D seismic land survey over an area of known hydrocarbon traps additionally proves the importance of 3‐D migration in stratigraphic imaging.

The influence of the planted geophone on seismic land data

Characteristics of the seismic data acquisition system that previously have been ignored become important as more sophisticated interpretive methods based on broader frequency bandwidths are developed to extract stratigraphic information from land data in hydrocarbon and mineral exploration. Theoretical and experimental results indicate that the geophone plant can be approximated by a damped oscillatory coupling, properties dependent upon the geophone mass, dimension of earth contact, and local soil consolidation. A massive geophone with minimal earth contact exhibits a low‐frequency plant resonance with weak damping and acts as a low‐pass filter to eliminate the high‐frequency components of a recorded signal. A lightweight geophone with large earth contact exhibits a high‐frequency plant resonance with strong damping and, consequently, filtering effects are minimal if the plant resonance is well above the signal bandwidth. Although signal filtering influences are weak for strong damping, phase delays can introduce errors of several milliseconds which resemble static errors. Additional complications arise since these time shifts are frequency dependent and, consequently, not identical for all reflection events in a seismic trace. The resonant frequency of the geophone plant increases with increased soil consolidation; however, damping demonstrates only a weak dependence upon consolidation. All of these factors can limit the effectiveness of common‐depth‐point (CDP) stacking methods if the proper technique is not practiced in the acquisition of broad‐bandwidth seismic data.

SEISMIC CREW SURVEY — MAY

SEG’s May 1977 survey of oil companies and domestic contractors shows a total of 301 seismic land crews and marine vessels operating in the U.S. and U.S. waters. This is the first time since February 1975 that the figure has risen above the 300 mark (Figure 1). This total is 22 percent above May 1976, 5 percent above May 1975, but still 4 percent below May 1974. Comparative figures of U.S. land crews and marine vessels are given in Table 1. Seismic crew data for May 1977 in Canada are shown in Table 2.

PROF. N. YAMASAKI'S CONTRIBUTION TO TECTONIC GEOMORPHOLOGY

Prof. Naomasa YAMASAKI (1870-1929), the founder of the Department of Geography, the University of Tokyo, was one of the pioneers of modern geography in Japan and was mainly interested in geomorphology. His studies in geomorphology were chiefly carried out on the following three subjects ; volcanoes, glacial and tectonic landforms. Prof. YAMASAKI, who started his academic works as a petrologist, surveyed geology of volcanoes in central Japan in the earlier stage of his research career. He explained the historical development of the volcanoes, describing topographic features as well as petrographic characteristics of their constituents. His descriptive studies of volcanic landscape were a model of geomorphological investigations of volcanoes in the earlier stage of Japanese geomorphology. In 1902, immediately after he came back from Europe, where he studied geography under the leadership of Profs. J. J. REIN and A. PENCK, he published a famous paper on glacial landf orms in Japan. In this paper he pointed out the existence of traces of former glaciers in high mountains of central Japan. Since then, studies on glacial topography were extraor-dinarily accelerated in Japan. In 1923, the southern part of the Kanto District was attacked by a severe earthquake, ac-companying remarkable land deformation. Prof. YAMASAKI surveyed characteristics of the seismic land deformation and found its close relationships with geomorphological and geological structure of the district. Afterward, he planned to carry out relevelling of bench marks along the coast of the Sea of Japan in order to detect chronic land deformation not associated with earthquakes. As a result of these investigations, he proposed an important idea on the devel-opment of tectonic landforms in Japan as follows. The earth's crust is being deformed acutely at times of earthquakes and chronically in aseismic periods, and such present land deformations are very similar in mode to crustal deformation by which tectonic landf orms have been formed. Present acute and chronic crustal movement therefore, must be successive in nature to mor-phogenetic crustal movement in the recent geological time. Stimulated by Prof. YAMASAKI's works, studies on tectonic landf orms have been one of the most interested research fields in Japanese geomorphology. Many important studies have been carried out on the geomorphological structure of the Japanese Islands, processes of morpho-genetic crustal movement in the recent geological time, and active faults and folds. As a result of these studies, Prof. YAMASAKI's idea on the development of tectonic landforms has been proved to be correct. Studies on tectonic landforms in Japan have just arrived in the stage which Prof. YAMASAKI was eager . to attain to, and will be developed into a new stage in near future, where the development of tectonic landforms will be synthetically investigated together with volcanic landscape in which he also was much interested.