TO TACKLE THE DECONVOLUTION PROBLEM — A POWERFUL METHOD BASED ON MORE GEOLOGICAL HYPOTHESES

1986 ◽  
Vol 26 (1) ◽  
pp. 192
Author(s):  
E. Denelle
Keyword(s):  
High Amplitude ◽  
Hydrocarbon Exploration ◽  
Reflection Coefficients ◽  
Seismic Section ◽  
Seismic Processing ◽  
Seismic Prospecting ◽  
Generalized Inversion ◽  
Reflectivity Spectra ◽  
Deconvolution Problem ◽  
Reflectivity Function

The new rules of the game in hydrocarbon exploration demand an exact positioning of the seismic markers in order to define the geometry of the targets more than ever before. However, the degree of success will depend to a great extent on how accurately the amplitude of reflection coefficients can be estimated.These new requirements mean that all stages of traditional seismic processing have to be critically evaluated. It can be seen, in particular, when assessing existing deconvolution methods for seismic processing, that they are often ill-conditioned to problems posed by the targets of stratigraphic exploration or by reservoir seismic prospecting. The amplitude of the reflectivity function is often estimated inaccurately.The approach described in this paper abandons the usual hypothesis (white reflectivity spectra) made by deconvolution methods and employs as alternative information the lateral redundancies which are always present on a seismic section. Our method first estimates the location of high amplitude reflectors with good lateral continuity, by means of an elegant automatic picking program. Based on these locations, a generalized inversion can be used to yield the wavelet emitted by the source, and the amplitude of the main reflection coefficients simultaneously for each trace. All the reflection coefficients are then estimated using the amplitudes and the wavelets computed previously.The various stages of this method which is called Deconvolution-Inversion, developed by Total Compagnie Française des Pétroles, are illustrated in the paper by means of both synthetic and real examples. The ability of the method to preserve the amplitudes makes it a powerful tool for stratigraphic and reservoir seismic prospecting purposes.

Geological origins of seismic bright spot reflections in the Ordovician strata in the Halahatang area of the Tarim Basin, western China

2018 ◽  
Vol 55 (12) ◽  
pp. 1297-1311 ◽  
Author(s):  
Wei Yang ◽  
Xiaoxing Gong ◽  
Wenjie Li
Keyword(s):  
Tarim Basin ◽  
Oil And Gas ◽  
High Amplitude ◽  
Hydrothermal Activity ◽  
Hydrocarbon Exploration ◽  
Western China ◽  
Bright Spot ◽  
Gas Reservoirs ◽  
Seismic Section ◽  
Bright Spots

Anomalously high-amplitude seismic reflections are commonly observed in deeply buried Ordovician carbonate strata in the Halahatang area of the northern Tarim Basin. These bright spots have been demonstrated to be generally related to effective oil and gas reservoirs. These bright spot reflections have complex geological origins, because they are deeply buried and have been altered by multi-phase tectonic movement and karstification. Currently, there is no effective geological model for these bright spots to guide hydrocarbon exploration and development. Using core, well logs, and seismic data, the geological origins of bright spot are classified into three types, controlled by karstification, faulting, and volcanic hydrothermal activity. Bright spots differing by geological origin exhibit large differences in seismic reflection character, such as reflection amplitude, curvature, degree of distortion, and the number of vertically stacked bright spots in the seismic section. By categorizing the bright spots and the seismic character of the surrounding strata, their geological origins can after be inferred. Reservoirs formed by early karstification were later altered by epigenetic karstification. Two periods of paleodrainage further altered the early dissolution pores. In addition, faults formed by tectonic uplift also enhanced the dissolution of the flowing karst waters. Some reservoirs were subsequently altered by Permian volcanic hydrothermal fluids.

APPLICATION OF THE EMPIRICAL MODE DECOMPOSITION METHOD TO GROUND-ROLL NOISE ATTENUATION IN SEISMIC DATA

2013 ◽  
Vol 31 (4) ◽  
pp. 619 ◽  
Author(s):  
Luiz Eduardo Soares Ferreira ◽  
Milton José Porsani ◽  
Michelângelo G. Da Silva ◽  
Giovani Lopes Vasconcelos
Keyword(s):  
Empirical Mode Decomposition ◽  
Seismic Data ◽  
Low Frequency ◽  
High Amplitude ◽  
Seismic Line ◽  
Seismic Processing ◽  
Mode Decomposition ◽  
Ground Roll ◽  
Fortran 90 ◽  
Emd Method

ABSTRACT. Seismic processing aims to provide an adequate image of the subsurface geology. During seismic processing, the filtering of signals considered noise is of utmost importance. Among these signals is the surface rolling noise, better known as ground-roll. Ground-roll occurs mainly in land seismic data, masking reflections, and this roll has the following main features: high amplitude, low frequency and low speed. The attenuation of this noise is generally performed through so-called conventional methods using 1-D or 2-D frequency filters in the fk domain. This study uses the empirical mode decomposition (EMD) method for ground-roll attenuation. The EMD method was implemented in the programming language FORTRAN 90 and applied in the time and frequency domains. The application of this method to the processing of land seismic line 204-RL-247 in Tacutu Basin resulted in stacked seismic sections that were of similar or sometimes better quality compared with those obtained using the fk and high-pass filtering methods.Keywords: seismic processing, empirical mode decomposition, seismic data filtering, ground-roll. RESUMO. O processamento sísmico tem como principal objetivo fornecer uma imagem adequada da geologia da subsuperfície. Nas etapas do processamento sísmico a filtragem de sinais considerados como ruídos é de fundamental importância. Dentre esses ruídos encontramos o ruído de rolamento superficial, mais conhecido como ground-roll . O ground-roll ocorre principalmente em dados sísmicos terrestres, mascarando as reflexões e possui como principais características: alta amplitude, baixa frequência e baixa velocidade. A atenuação desse ruído é geralmente realizada através de métodos de filtragem ditos convencionais, que utilizam filtros de frequência 1D ou filtro 2D no domínio fk. Este trabalho utiliza o método de Decomposição em Modos Empíricos (DME) para a atenuação do ground-roll. O método DME foi implementado em linguagem de programação FORTRAN 90, e foi aplicado no domínio do tempo e da frequência. Sua aplicação no processamento da linha sísmica terrestre 204-RL-247 da Bacia do Tacutu gerou como resultados, seções sísmicas empilhadas de qualidade semelhante e por vezes melhor, quando comparadas as obtidas com os métodos de filtragem fk e passa-alta.Palavras-chave: processamento sísmico, decomposição em modos empíricos, filtragem dados sísmicos, atenuação do ground-roll.

Shallow seismic reflection study of a glaciated valley

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1395-1407 ◽  
Author(s):  
Frank Büker ◽  
Alan G. Green ◽  
Heinrich Horstmeyer
Keyword(s):  
Seismic Reflection ◽  
High Amplitude ◽  
Data Sets ◽  
Seismic Section ◽  
Data Set ◽  
Seismic Reflection Data ◽  
Northern Switzerland ◽  
Reflection Data ◽  
Shallow Seismic ◽  
Glaciated Valley

Shallow seismic reflection data were recorded along two long (>1.6 km) intersecting profiles in the glaciated Suhre Valley of northern Switzerland. Appropriate choice of source and receiver parameters resulted in a high‐fold (36–48) data set with common midpoints every 1.25 m. As for many shallow seismic reflection data sets, upper portions of the shot gathers were contaminated with high‐amplitude, source‐generated noise (e.g., direct, refracted, guided, surface, and airwaves). Spectral balancing was effective in significantly increasing the strength of the reflected signals relative to the source‐generated noise, and application of carefully selected top mutes ensured guided phases were not misprocessed and misinterpreted as reflections. Resultant processed sections were characterized by distributions of distinct seismic reflection patterns or facies that were bounded by quasi‐continuous reflection zones. The uppermost reflection zone at 20 to 50 ms (∼15 to ∼40 m depth) originated from a boundary between glaciolacustrine clays/silts and underlying glacial sands/gravels (till) deposits. Of particular importance was the discovery that the deepest part of the valley floor appeared on the seismic section at traveltimes >180 ms (∼200 m), approximately twice as deep as expected. Constrained by information from boreholes adjacent to the profiles, the various seismic units were interpreted in terms of unconsolidated glacial, glaciofluvial, and glaciolacustrine sediments deposited during two principal phases of glaciation (Riss at >100 000 and Würm at ∼18 000 years before present).

DECOMPOSITION AND SUPPRESSION OF MULTIPLE REFLECTIONS

Geophysics ◽  
1965 ◽  
Vol 30 (1) ◽  
pp. 54-71 ◽  
Author(s):  
R. J. Watson
Keyword(s):  
Reflection Coefficients ◽  
Detailed Knowledge ◽  
Multiple Reflections ◽  
Surface Reflection ◽  
Multiple Function ◽  
First Order ◽  
Positive Feedback Circuit ◽  
Reflectivity Function ◽  
Correlation Search ◽  
Order Surface

Multiple reflections constitute an important source of “noise” on seismograms. Because multiples are related to the primary reflectivity function r(t) in a very complicated way, the suppression of all multiple reflections on a single seismic trace is unlikely without a detailed knowledge of the reflectivity function itself. This paper describes a series of approximations in which multiple reflections are decomposed into component subsets. For certain types of velocity functions, one or two of these subsets form a sufficiently good approximation to the complete multiple process to at least predict the strongest multiples present on a field seismogram. The subset approximations to the complete multiple function include the first‐order surface multiples, i.e., three‐bounce multiples having a second reflection at the surface. The expression for this set of multiples is [Formula: see text], where the * stands for convolution, and [Formula: see text] is the surface reflection coefficient. Computations of this set are compared with the complete multiple function for logs from Alberta, Canada, and southern Mississippi. A further approximation, called the [Formula: see text], is valid in areas where a few reflection coefficients, r⁁(t), are responsible for the bulk of the multiple noise. [Formula: see text] consists of all first‐order surface multiples which have a contribution from the r⁁(t) zone. The above‐mentioned velocity logs are used to illustrate the [Formula: see text] approximation. The [Formula: see text] function is compared with the complete first‐order surface multiple function for the two logs. A method for suppressing the multiples described by the approximations is proposed. The technique is illustrated for the [Formula: see text] approximation but can be extended to higher‐order approximations. It consists of a positive feedback circuit in which a reflectivity function is simulated along with appropriate time‐variant gain adjustments. In order to realize the computation, it is necessary to find the time and amplitude of the reflection coefficients responsible for the large‐amplitude multiple reflections. Several methods for providing this information are discussed and a correlation search technique is illustrated with examples. Finally, the suppression technique is illustrated with live seismic data on two record sections from two different areas showing data before and after multiple suppression. In both cases the [Formula: see text] approximation was adequate.

THE KURTOSIS OF REFLECTION COEFFICIENTS IN A FRACTAL SEQUENCE OF SEDIMENTARY LAYERS

Fractals ◽  
1993 ◽  
Vol 01 (02) ◽  
pp. 263-268 ◽  
Author(s):  
G. KORVIN
Keyword(s):  
Reflection Coefficient ◽  
Reflection Coefficients ◽  
Measured Signal ◽  
Seismic Processing ◽  
Reflection Seismic ◽  
Basic Task ◽  
Sedimentation Model ◽  
Unknown Sequence

In the reflection seismic technique of hydrocarbon prospecting, the measured signal is the convolution of an unknown sequence of reflection coefficients by a statistically known source signature. A basic task of seismic processing is to estimate the sequence of reflection coefficients. The aim of this paper is to show that in case of a fractal sedimentation model, the conventional statistical descriptors (variance, skewness, kurtosis) of the reflection coefficient sequence are strongly dependent on, or are even divergent functions of, the resolution.

scholarly journals Integration and Interpretation of Aeromagnetic, 3D Seismic and Well Logs Data in Hydrocarbon Exploration in Niger Delta Basin

2020 ◽  
pp. 28-42
Author(s):  
Oluwatoyin O. Akinsete ◽  
Toyin Y. Abdulraheem ◽  
Salawu B. Naheem ◽  
Adebiyi S. Leke
Keyword(s):  
Niger Delta ◽  
Energy Demand ◽  
Effective Porosity ◽  
Hydrocarbon Exploration ◽  
Well Logs ◽  
Neutron Density ◽  
3D Seismic ◽  
Oil Accumulation ◽  
Seismic Section ◽  
Hydrocarbon Saturation

As the challenges associated with hydrocarbon exploration rises with upsurge in energy demand, the need to minimize risk associated with hydrocarbon exploration if supply is to keep up with demand. In this work, high resolution aeromagnetic, 3D seismic and well-logs data were adopted and integrated to aid in exploration and characterization of reservoirs in ''XYZ'' field in offshore Niger Delta. Fast Fourier Transform Filter using Oasis Montaj software was applied to the Total Magnetic Intensity grid in horizon and fault interpretation also used to produce subsurface structural maps for sedimentary layer thickness estimation. Direct hydrocarbon indicators (bright spots) on the seismic section was shown using seismic signal. Petrel software and wireline log signatures were used to identify hydrocarbon-bearing sands and determine petrophysical parameters such as porosity, hydrocarbon saturation and net thickness. The structural maps generated showed: Three major (synthetic) faults dips south and one minor (antithetic) fault dips north in the field; three identified prospective sands (A, B, C) were delineated. Possible presence of oil accumulation was indicated by the combined Neutron-Density log response. The range of values of effective porosity, hydrocarbon saturation and net thickness were 18-22%, 34-58% and 19.1-28.1 m, respectively.  This study established that integration of magnetic, 3D seismic and well-log data are desirable innovative techniques to better understand and analyze subsurface for hydrocarbon potential and exploration.

scholarly journals Seismic Signature of Transition Zone (Wolf Ramp) in Shale Deposits with Application of Frequency Analysis

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Anna Kwietniak ◽  
Tomasz Maćkowski ◽  
Kamil Cichostępski
Keyword(s):  
Reflection Coefficient ◽  
Transition Zone ◽  
Seismic Analysis ◽  
High Amplitude ◽  
Seismic Interpretation ◽  
Seismic Survey ◽  
Baltic Basin ◽  
Linear Change ◽  
Seismic Section ◽  
Reservoir Volume

The concept of a transition zone, known as Wolf ramp, was incorporated into the seismic interpretation of a 3D seismic survey situated within the Baltic Basin (Northern Poland). Within the survey area, there exists one formation, the Pasłęk Formation, (Lower Silurian—Llandovery), that exhibits a linear change of velocity. This characteristic—linear change of velocity—causes a reflection coefficient (i.e., seismic amplitude) produced at such a boundary to be frequency dependent. The Pasłęk Formation was considered to be a potential shale gas reservoir and it was necessary to determine its structural position and thickness. The formation is challenging for robust seismic interpretation on the migrated seismic section—it does not manifest a stable reflection coefficient, and the amplitude contrast associated with the borders of the formation is low. There is no impedance contrast that would produce a reflection of high amplitude at the top or base of the formation which excludes determination of the formation thickness, hence the estimation of reservoir volume. Within a 3D dataset, there exists only one well with complete logs that were used for the analysis. The Pasłęk Formation is a flat-lying layer that continues itself far beyond the 3D survey. It is present in wells in the vicinity of the study area. These wells lay within other 3D or 2D datasets, but the quality of the seismic is poor, and similar seismic analysis is not possible. Nevertheless, these wells were incorporated in the research to reason about the possible link between the existence of transition zone and mineral content. The method used for recognition of transition zone is spectral decomposition and spectral analyses. The integrated studies enabled us to find a link between the Wolf ramp and mudstone-claystone interval of the Silurian age and give a new example of a transition zone which is present in shale plays. The transition zone concept might be applied for shale plays identification and analysis.

scholarly journals Investigation of Pore Pressure on Seismic Amplitude Response: A Well-Based Modeling Case Study of Sojuko Field, Niger Delta

2019 ◽  
Vol 11 (3) ◽  
pp. 36
Author(s):  
Difference O. Ogagarue
Keyword(s):  
Pore Pressure ◽  
Niger Delta ◽  
Oil Sands ◽  
Hydrocarbon Exploration ◽  
Pressure Effects ◽  
Reflection Coefficients ◽  
Angle Of Incidence ◽  
Offshore Area ◽  
Seismic Amplitude ◽  
Well Data

The Sojuko field was discovered in 2001 in the eastern shallow offshore area of the Niger Delta, Nigeria. Three (3) exploration wells have so far been drilled in the field, two (2) of which are reasonably vertical and the third highly deviated. Three (3) key reservoirs which are laterally continuous across the wells have been identified with proven oil and gas reserves. Pore pressure data from repeat formation test (RFT) measurements acquired in the deviated well show that the wells are entirely hydrostatic to true depth (TD). This research focuses on investigating how seismic amplitudes change with offset/angle of incidence in relation to varying pore pressure regimes at the shale-hydrocarbon sand and shale-brine sand interfaces using well data. The aim is to aid quantitative interpretation in an on-going field-wide exploration drive to de-risk hydrocarbon exploration in the deeper plays in the area which are below TD, and are expected to be overpressured. The study is hinged on end-member shale elastic parameter substitution in which the shales are subjected to varying overpressure regimes while keeping the reservoirs (sands) at in situ (hydrostatic) condition. The end-member shale property substitution simulated shale compaction dis-equilibrium as the main overpressure generation mechanism in this study. The results show that top gas sands, top oil sands and top brine sands would be visible on seismic in the deeper plays where pore pressures are expected to be very high, but with distinctive seismic amplitude with offset/angle behavior. The top gas sands are visible as blue loop with small positive reflection coefficients at the near offsets/angles, but with polarity reversal to red loop with negative reflection coefficients which become more and more negative at the far angles at hard overpressure regimes. Top oil sands are recognized as blue loop with large positive reflection coefficients at the near angles; the coefficients becoming less and less positive at the far angles/offsets. The top oil sands may not be detected on seismic at the far angles/offsets unless at very hard overpressures. Brine sands have similar seismic response as oil sands at hard overpressures, but can be distinguished from oil sands based on their much higher amplitudes over the entire offset/angle range. The study is also aimed at removing uncertainty in seismic-based pore pressure quantification at the deeper targets where there is absence of well data for calibrating pore pressure effects at varying conditions.

scholarly journals SEISMIC SIGNAL ANALYSIS USING MINIMUM PHASE AND SINGULAR VALUE DECOMPOSITION METHODS. APPLICATION TO GROUNDROLL ATTENUATION

2019 ◽  
Vol 37 (2) ◽  
Author(s):  
Anderson Silva Santos ◽  
Milton José Porsani
Keyword(s):  
Singular Value Decomposition ◽  
Seismic Data ◽  
Seismic Signal ◽  
Singular Value ◽  
Frequency Noise ◽  
Minimum Phase ◽  
Phase Decomposition ◽  
Seismic Section ◽  
Reflectivity Function ◽  
Value Decomposition

ABSTRACT. A challenge in land seismic data processing is the coherent noise groundroll. This noise is related to the propagation of surface waves of the Rayleigh type, this undesired event has as characteristics: low frequencies, high amplitudes and strong dispersion, which masks the events of interest in the stacked seismic section. The seismic data from the Tacutu Basin, besides having a low signal-to-noise ratio, are also strongly contaminated by groundroll noise, which makes it a challenge to obtain stacked seismic section with high resolution of this sedimentary basin. The 1D and 2D frequency filters are widely used for groundroll attenuation, but these methods besides attenuating the noisy also eliminate part of the signal by rejecting part of the frequency band of the seismic signal. Therefore, we are introduce a new filter to groundroll attenuation that uses two powerful tools for decomposition of the seismic signal together, minimum phase decomposition and singular value decomposition. The proposed method aims to estimate the reflectivity function for each seismic trace and then perform a decomposition of this reflectivity function. Since the low frequency noise is confined in the first portion of the decomposed signal it is possible to make a separation between the noise and the signal. The filtering method was included in the 2D seismic processing flow chart of the Tacutu Basin. The results showed that the proposed method was capable of attenuate the groundroll noise and generated at the end a stacked seismic section with a good resolution. Keywords: minimum phase decomposition, singular value decomposition, groundroll attenuation.RESUMO. Um desafio no processamento de dados sísmicos terrestres é o ruído coerente groundroll. Este ruído está relacionado à propagação de ondas de superfície do tipo Rayleigh, este evento indesejado tem como características: baixas frequências, altas amplitudes e forte dispersão, o que mascara os eventos de interesse na seção sísmica empilhada. Os dados sísmicos da Bacia do Tacutu, além de apresentar uma baixa relação sinal-ruído, também estão fortemente contaminados pelo ruído do solo, o que dificulta a obtenção de seções sísmicas empilhadas com alta resolução desta bacia sedimentar. Os filtros de frequência 1D e 2D são amplamente utilizados para a atenuação do groundroll, mas esses métodos além de atenuar o ruído também eliminam parte do sinal rejeitando parte da banda de frequência do sinal sísmico. Portanto, estamos introduzindo um novo filtro para a atenuação de groundroll que usa duas ferramentas poderosas para a decomposição do sinal sísmico, decomposição em fase mínima e decomposição em valor singular. O método proposto tem como objetivo estimar a função de refletividade para cada traço sísmico e então realizar a decomposição dessa função refletividade. Uma vez que o ruído de baixa frequência é confinado na primeira porção do sinal decomposto, é possível fazer uma separação entre o ruído e o sinal. O método de filtragem foi incluído no fluxograma de processamento sísmico 2D da Bacia do Tacutu. Os resultados mostraram que o método proposto foi capaz de atenuar o ruído groundroll e gerar ao final uma seção sísmica empilhada com boa resolução.Palavras-chave: decomposição em fase mínima, decomposição em valores singulares, atenuação do groundroll.  

High-resolution 2D seismic imaging and forward modeling of a polymetallic sulfide deposit at Garpenberg, central Sweden

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. B339-B350 ◽  
Author(s):  
Omid Ahmadi ◽  
Christopher Juhlin ◽  
Alireza Malehmir ◽  
Mie Munck
Keyword(s):  
High Resolution ◽  
Ray Tracing ◽  
Synthetic Data ◽  
Forward Modeling ◽  
High Amplitude ◽  
Seismic Profile ◽  
P Wave ◽  
Sulfide Deposit ◽  
Seismic Section ◽  
Ore Body

We acquired a high-resolution 2D seismic profile to test the capability of the seismic method in imaging a sulfide ore body at Garpenberg, central Sweden. Delineation of the geologic structures, which surround and host the ore body, is another goal of the survey. Due to the 3D geology of the structures, a cross-dip correction performed to image out-of-the-plane reflections, resulting in a clear high amplitude anomaly at a time and location to that to be expected from near the top of the ore body. Furthermore, DMO processing and migration are applied to the data, providing images of four main reflection groups. The reflections have been interpreted as corresponding to geologic rock units in the area that partly interfere with the potential ore body signal. To further investigate the seismic response of the ore body, forward modeling by ray-tracing is applied using the ore body geometry as mapped by drilling. We use two ray-tracing approaches: standard 3D ray-tracing and an exploding reflector approach. Seven representative samples from the mine area are used to determine P-wave velocities. The measurements show a considerable contrast between the ore body and host rock. By comparing the modeled and observed data, we find that the high amplitude signal in the real seismic section most likely emanates from near the top of one concentrated ore which lies inside the larger mapped ore body that has been modeled as a resource. The base of the ore body is only observed on the synthetic data whereas a signal penetration analysis suggests that the seismic signal penetrated efficiently along the entire survey line. Presence of disseminated ore and lower fold toward the northern end of the profile could be combined reasons that make imaging the base of the ore body difficult.

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