Marine Seismic Data Processing Research Articles

Processing and interpretation of vintage 2D marine seismic data from the outer Hanö Bay area, Baltic Sea

A grid of previously unpublished, vintage 2D marine seismic lines has been processed and interpreted to the east of Hanö Bay, SW Baltic Sea. The 3200 km 2 study area lies on the transition between the Hanö Bay Basin to the West and Baltic Synelcise to the East, NE of the Tornquist intra shield tectonic zone. Data from the NA79, NA80 and RW84 surveys were selected for this study from the extensive Oljeprospektering AB (OPAB) Baltic Sea dataset. New processing workflows have been developed for the data which focus on suppressing two significant forms of noise, namely multiple and side scattered noise. Deconvolution in the tau-p domain, parabolic radon demultiple and post stack deconvolution are shown to be effective at attenuating multiple noise, while FK filtering in shot and receiver gathers is effective at removing side scattered noise. The newly processed data were interpreted and a series of maps detailing the structure of the basement, Cambrian and Silurian/Paleozoic horizons were constructed. These maps differ significantly to previously published interpretations of the area. Within the study area, a region of significant Late Carboniferous/Early Permian transtensional faulting and Late Cretaceous inversion is mapped in detail. This structure would have exhibited normal offsets of up to 600 m before inversion with later inverted displacements of up to approximately 200 m in places. This feature appears to extend some 20 km to the SW of the study area to the major fault bounding the Christiansø High. Based on the seismic interpretation, the area appears to have had a similar overall geological history as the adjacent Tornquist Zone to the SW. • A grid of 2D lines is processed and interpreted from the outer Hanö Bay area. • Key data issues are multiple and side scattered noise and large receiver spacing. • Parabolic radon demultiple, tau-p deconvolution and FK filtering are used. • A zone of major late Palaeozoic faulting and late Cretaceous inversion is mapped.

The influence of sea water velocity variation on seismic traveltimes, ray paths, and amplitude

The main factors affecting seismic exploration is the propagation velocity of seismic waves in the medium. In the past, during marine seismic data processing, the propagation velocity of sea water was generally taken as a constant 1500 m/s. However, for deep water exploration, the sound velocity varies with the season, time, location, water depth, ocean currents, and etc.. It also results in a layered velocity distribution, so there is a difference of seismic traveltime, ray paths, and amplitude, which affect the migration imaging results if sea water propagation velocity is still taken as constant for the propagation wavefield. In this paper, we will start from an empirical equation of seismic wave velocity in seawater with changes of temperature, salinity, and depth, consider the variation of their values, build a seawater velocity model, and quantitatively analyze the impact of seawater velocity variation on seismic traveltime, ray paths, and amplitude in the seawater velocity model.

Advances in seismic imaging through basalts: a case study from the Faroe–Shetland Basin

New seismic reflection data have been used to image intra- and sub-basalt features beneath the Faroe–Shetland Basin in the North Atlantic, where the highly reflective top and base boundaries of flood basalts and their complex internal structure make successful seismic imaging difficult. This study demonstrates that appropriate acquisition and processing of marine seismic data from hydrophone streamers and ocean-bottom seismometers (OBS) has the potential to enhance significantly imaging of intra-basalt and sub-basalt seismic reflections. The intersection of a new seismic reflection profile recorded in 2002 with a seismic profile recorded in 1998 allows a direct comparison of advances in sub-basalt imaging over this period and an interpretation of geological structures and seismic velocities at the intersection. To achieve better resolution of sediments below basaltic layers, surface seismic reflection data using a broad-band, low-frequency source have been recorded. By using a source wavelet with a significantly enhanced frequency spectrum centred at 10 Hz, generated from a large (167 l) airgun array tuned to the first bubble pulse, a wavelet is produced that is capable of penetrating through thick basaltic sequences. Furthermore, recording the low-frequency reflections to large offsets along a 12 000 m long streamer with 3.125 m single sensor spacing allowed effective suppression of multiple reflections, enhanced the precision of velocity analyses and produced better migration results. Seismic data along the same profile were also recorded on a dense deployment of 85 four-component OBS at 2 km or 6 km station spacing. These complementary ocean-bottom data allowed the large-scale velocity variations within and beneath the basalt to be constrained by recording at large offsets the termination of the diving rays ( c . 18 km) propagating through the basalt. Integration of seismic reflection data and OBS recordings yields good seismic velocity estimates and, therefore, increased confidence in the interpretation of intra- and sub-basalt features and lithology. Four major stratigraphic units characterized by their seismic velocities and reflection characters were identified: (a) post-basalt sediments; (b) basalt sequence; (c) sub-basalt unit; and (d) the top of presumed Cretaceous basement. The top boundary of the basalt sequence is defined by a strong reflection with a steep velocity increase from 3.5 km s −1 to 4.5 km s −1 in the c . 200 m thick layer above it. The basalt sequence here is c . 2.5 km thick. Beneath the base of the basalt there is a velocity decrease from 5.8 km s −1 to 5.2 km s −1 . The sub-basalt unit is subdivided further into hyaloclastites mixed with sediments and sills, and sub-basalt sediments separated by another velocity inversion from 5.2 km s −1 to 4.5 km s −1 . The Cretaceous basement with velocities above 5.5 km s −1 lies underneath these sub-basalt sediments.

Deconvolução preditiva de dados GPR adquiridos sobre lâmina d'água: exemplo do Rio Taquari, Pantanal Matogrossense

Neste trabalho apresentamos resultados obtidos com a aquisição e o processamento de dados de radar de penetração no solo (GPR - Ground Penetrating Radar) registrados sobre as águas do Rio Taquari, na Planície do Pantanal Matogrossense. Esta modalidade não convencional de utilização do método GPR, demonstrou ser bastante viável e permitiu estabelecer alguns parâmetros ótimos para a aquisição de dados GPR sobre a lâmina d'água, podendo servir de guia para os futuros trabalhos de GPR em regiões similares. As seções obtidas permitiram identificar claramente algumas estruturas no leito do Rio Taquari, tais como bancos de areia e canais do rio, além de reflexões primárias e fortes eventos correspondentes a reflexões múltiplas. Para remoção das reflexões múltiplas, presentes nas seções GPR, utilizamos o método de filtragem denominado deconvolução preditiva (DP) de Wiener-Levinson que possui seu uso consagrado na indústria do petróleo para processamento de dados sísmicos marítimos. A DP de Wiener-Levinson, nas modalidades mono e multicanal, foram aplicadas sobre três seções fluviais de dados GPR. As seções deconvolvidas demonstraram que a atenuação das reflexões múltiplas nos radargramas foi mais eficaz em regiões onde não ocorrem variações abruptas no leito do rio e a espessura da lâmina d'água é superior a dois metros. Embora este trabalho tenha sido de caráter local, os resultados promissores obtidos, com o método de DP de Wiener-Levinson, mono e multicanal, sugerem o emprego desta metodologia como uma ferramenta eficaz na remoção de reflexões múltiplas presentes em dados GPR adquiridos sobre a superfície de rios e lagos.

Surface-Related Multiple Elimination – Applications to an offshore Australia data set

The presence of free-surface-related wave phenomena is a classic problem in marine seismic data processing. Over the years, the industry has relied heavily on conventional multiple suppression methods such as predictive deconvolution and differential move-out filtering to remove surface-related multiples from marine seismic data. These methods are based on rather specific assumptions about the subsurface and characteristic differences between primaries and multiples. Since these assumptions are often not met in the field, the effectiveness of these methods may be limited. Surface-Related Multiple Elimination (SRME) is a relatively new method that removes all surface-related multiples,without using any additional information about the subsurface. Application of SRME to offshore Australia data sets results in much improved results, where relatively weak primary reflections become more interpretable.

On: “A new insight into the reciprocity principle” (Børge Arntsen and José M. Carcione, GEOPHYSICS, 65, 1604–1612).

Reciprocity is an important property of elastodynamic, electromagnetic, and acoustic wavefields. Combined with optimization techniques, reciprocity theorems can be regarded as providing the basic ingredients to imaging and inversion methods in geophysical exploration and remote sensing (de Hoop, M. V. and de Hoop, A. T., 2000). Furthermore, reciprocity serves as the basis for the elimination procedures of surface‐related multiples in marine seismic data processing (Fokkema and van den Berg, 1993). In view of all this, a thorough and elucidating discussion on the configurations to and the conditions under which reciprocity applies, and what reciprocity leads to, like the recent paper by Arnsten and Carcione (2000), serves a useful purpose. In this paper, also a number of interesting applications are worked out in detail. The aim of this discussion is to indicate briefly how some of the results obtained in that paper are related to the ones that the present author has presented in de Hoop (1995), a reference that does not appear in Arntsen and Carcione (2000).

A HIGH RESOLUTION MARINE SEISMIC SURVEY *

AbstractSub‐bottom profilers achieve high resolution but limited penetration beneath the seabed. Marine seismic surveys with long streamers and conventional sources suffer from an incomplete CDP stack and an unnecessarily low signal frequency in the early part of the section. Consequently there is a depth interval over which the optimum resolution of the seismic reflection method is not achieved. This paper describes the design, conduct, and results of an experimental survey made to obtain high resolution sections (predominant frequency about 200 Hz) with reflection times up to one second in the northern North Sea. The prime motivation for the experiment was to assess the possibility of mapping a shallow gas sand which had been encountered by the drillers.The design concept of the survey was to keep all the benefits of conventional marine seismic data gathering and processing, but to reduce their dimensions and time scales by a factor of five to ten. The survey in 1972 recorded a total of twenty‐four lines using twenty‐four fold cover with 5 m spacing between the reflector points, and a separation of 50 m between adjacent lines. Multi‐electrode sparkers were used with a shallow purpose‐built twenty‐four channel 240 m hydrophone streamer. The recording sample interval was 1 ms. The final sections, obtained after conventional data processing, were of good quality. The results of velocity analysis helped to distinguish primary and multiple energy. Reflections with large negative reflection coefficients were seen in some parts of the survey area, and these are thought to indicate thin gas sands.

PROCESSING OF MARINE SEISMIC DATA FROM AREAS WITH LARGE AND RAPID VARIATION IN WATER DEPTH

The offshore search for oil and gas is progressively moving further out to sea as near-shore structures are delineated and drilled. Prospects that overlap the edge of the continental shelf and slope will more than likely present problems in the processing of marine seismic data because of large and rapid variation in water depth.Magellan Petroleum encountered such difficulties in the digital computer processing of its East Gippsland Basin Prospect which is located some 50 miles southeast of the Victoria coastline.A series of problems developed when an integrated computer program sequence or "package" was applied to the data. It was found that first break suppression schedules, deconvolution design gates, band-pass filter application gates and velocity functions could not be changed often enough due to program restrictions.Where the water bottom topography was rough, the restriction of submitting only three or four water depths to vary the velocity function and subsequent calculation of normal move-out corrections resulted in questionable accuracy for the corrected results.Sometimes, water bottom variations required individual trace static corrections which were not available in this particular "package" processing.Water bottom multiple periods vary as rapidly as the surface that generates them. A meticulous selection of the parameters of deconvolution programs is necessary to attenuate multiples under such conditions. Also close examination of the purposes and consequently methods of deconvolution computer programs is necessary to maximize the effectiveness of this powerful processing tool.Diffractions are frequently generated at points on an irregular sea bottom surface. Such detractions mask true water bottom reflections in deeper water and thus decrease the geophysicist's ability to process data accurately where computer programs require true water bottom depth.Presentation of record sections which illustrate problems and their probable solutions comprise a major part of this paper.

Dereverberation by Linear Systems Techniques

A linear system approach is presented for the modeling of a stationary layered medium assuming representation by a finite number of thin layers and wave propagation normal to these layers. A linear recursive mathematical model is developed and a method for the identification of parameters is discussed. The results, although specifically derived for the processing of marine seismic data, are applicable to similar type problems in communications and remote sensing.