Shallow Imaging of Gas and Hydrate Using the Deep-towed ACS Data in Joetsu Basin, Niigata, Japan

2021 ◽  
Author(s):  
Fernando Hutapea ◽  
Takeshi Tsuji ◽  
Masafumi Katou ◽  
Eiichi Asakawa
Keyword(s):  
Seismic Source ◽  
Frequency Component ◽  
Depth Information ◽  
Seismic Attribute ◽  
Processing Scheme ◽  
Free Gas ◽  
Reflection Amplitude ◽  
Hyperbolic Curve ◽  
Seismic Acquisition ◽  
Gas Chimneys

<p>The deep-towed Autonomous Continuous Seismic (ACS) is a deep-towed marine seismic acquisition method. The ACS utilizes high frequency seismic source (ranging from 700 Hz to 2300 Hz) and multi-channel receivers that both source and receivers can be located close the seafloor. Moreover, the ACS is suitable to obtain high-resolution image of shallow geological structures. Since ACS data acquisition can be operated near the seafloor, the ocean (strong) current makes the position of both receivers and sources irregular (unstable) and it is hard to measure the absolute depth of both receivers and sources. During data processing, the unstable depth of both sources and receivers not only make the recorded seismic reflection curve (hyperbolic curve) rugged, but also makes the velocity analysis process more difficult because the velocity semblance is not clear. In this study, we propose a processing scheme to solve the unstable source–receiver position problem and thus to construct an accurate final stack profile (Hutapea et al., 2020 doi:10.1016/j.jngse.2020.103573). We used deep-towed ACS data acquired in the Joetsu Basin in Niigata, Japan, where hydrocarbon features in the form of gas chimneys, gas hydrate, and free gas have been observed. Furthermore, sidelobes in the ACS source signature defocus the source wavelet and decrease the bandwidth frequency content. We designed a filter to focus the source signature. Our proposed approach considerably improved the quality of bandwidth frequency of the source signature and the final stacked profile. Even though depth information was not available for all receivers, the velocity semblance was well focused. Our seismic attribute analyses for the final stack section shows that free gas accumulations are characterized by low reflection amplitude and an unstable frequency component, and that hydrate close to the seafloor can be identified by its high reflection amplitude.</p>

Wavefield decomposition based on acoustic reciprocity: Theory and applications to marine acquisition

Geophysics ◽  
2013 ◽  
Vol 78 (2) ◽  
pp. WA41-WA54 ◽  
Author(s):  
Roald Gunnar van Borselen ◽  
Jacob Fokkema ◽  
Peter van den Berg
Keyword(s):  
Free Surface ◽  
Seismic Source ◽  
Sensor Data ◽  
Constant Depth ◽  
Seismic Acquisition ◽  
Single Sensor ◽  
Recorded Data ◽  
Marine Seismic ◽  
Wavefield Decomposition ◽  
Multisensor Data

In marine seismic acquisition, the free surface generates seismic events in our recorded data that are often categorized as noise because these events do not contain independent information about the subsurface geology. Ghost events are considered as such noise because these events are generated when the energy generated by the seismic source, as well as any upgoing wavefield propagating upward from the subsurface, is reflected downward by the free surface. As a result, complex interference patterns between up- and downgoing wavefields are present in the recorded data, affecting the spectral bandwidth of the recorded data negatively. The interpretability of the data is then compromised, and hence it is desirable to remove the ghost events from the data. Rayleigh’s reciprocity theorem is used to derive the relevant equations for wavefield decomposition for multisensor and single-sensor data, for depth-varying and depth-independent recordings from marine seismic experiments using a single-source or dual-source configuration. A comparison is made between the results obtained for a 2D synthetic example designed to highlight the strengths and weaknesses of the various acquisition configurations. It is demonstrated that, using the proposed wavefield decomposition method, multisensor data (measurements of pressure and particle velocity components, or multidepth pressure measurements) allow for optimal wavefield decomposition as independent measurements are used to eliminate the interference patterns caused by the free surface. Single-sensor data using constant-depth recordings are found to be incapable of producing satisfactory results in the presence of noise. Single-sensor data using a configuration with depth-varying measurements are able to deliver better results than when constant-depth recordings are used, but the results obtained are not of the same quality when multisensor data are used.

SPECTRAL ANALYSIS AND FORECASTING OF THE 25TH SOLAR CYCLES

2021 ◽  
Vol 44 ◽  
pp. 96-99
Author(s):  
D.B. Rozhdestvensky ◽  
◽  
V.I. Rozhdestvenskaya ◽  
V.A. Telegin ◽  
◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Fourier Series ◽  
Solar Activity ◽  
Digital Filtering ◽  
Frequency Component ◽  
Wolf Number ◽  
Complex Signal ◽  
Data Set ◽  
Processing Scheme ◽  
Spectral Ranges

In the present work, we propose an extrapolation method, developed on the basis of spectral analysis, digital filtering, and the principle of demodulation of a complex signal, for predicting the beginning of cycle 25 of solar activity. The Wolf number and other measured characteristics of solar activity have a very complex spectral composition. The Sun, by the nature of its radiation, contributes a significant stochastic component to the observational data. The experimental data are known only up to the present, and the prediction is about bridging the gap in our data set. Mathematically, the prediction problem boils down to extrapolation of discontinuous functions, which leads to a Gibbs phenomenon that occurs at the point of discontinuity and makes prediction into the future impossible. To overcome this discontinuity, additional physical models describing a continuous process are most often used. This paper uses only the Wolf series of numbers from 1818 to 2020. The authors developed an original forecasting technique using Fourier series, digital filtering and representation of the complex process as modulated and subsequent demodulation. As a result of decomposing the complex signal by Fourier series into separate components, the spectral ranges characteristic of the Wolf number were singled out. Taylor's series was used for construction of prediction or extrapolation algorithms. The extraction of spectral ranges, characteristic for the investigated process, is carried out by means of sequential digital filtering methods and information compression in accordance with the cut-off frequency of the digital filter. For example, when selecting eleven-year cycles of solar activity, we have to compress the information by a factor of 160. With such a processing scheme, the forecasting starts with the ultralow-frequency component with a period of more than 11 years, successively moving to the ranges of higher frequencies. The use of spectral analysis and Chebyshev filtering showed the possibility to predict the low-frequency component for the full cycle period. The eleven-year component forecast obtained by the authors is in good agreement with the data of the Brussels Royal Center.

High-resolution seismic reflection data acquisition and interpretation, Lake Neusiedl, Austria, northwest Pannonian Basin

2018 ◽  
Vol 6 (1) ◽  
pp. SB77-SB97 ◽  
Author(s):  
Johannes Loisl ◽  
Gabor Tari ◽  
Erich Draganits ◽  
András Zámolyi ◽  
Ingrid Gjerazi
Keyword(s):  
High Resolution ◽  
Seismic Reflection ◽  
Single Channel ◽  
Pannonian Basin ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Air Gun ◽  
Seismic Acquisition ◽  
Multichannel Seismic Reflection Data ◽  
Gas Chimneys

A combined 400+ km of single- and multichannel seismic reflection data were acquired on Lake Neusiedl in northeast Austria in May 2013. This geophysical campaign was a multinational academic effort among the Universities of Vienna, Budapest, Bremen, and Southampton. Lake Neusiedl is an exceptionally shallow lake, with an average water depth of only approximately 1.4 m. Although high-resolution single-channel seismic reflection data have been collected before on this lake, the multichannel seismic acquisition, towing a 60 m cable and an air gun behind a retrofitted ferry boat, was a completely new approach in this area. The quality of the multichannel data turned out to be exceptionally good; i.e., the high-frequency data illuminated the subsurface of the lake for the first time, down to the pre-Cenozoic basement at approximately 600 m depth. The most prominent findings of the new data include (1) a consistent southeasterly dip of erosionally truncated Late Miocene (Pannonian) sediments beneath a very thin Holocene mud layer, (2) the presence of major throughgoing fault systems (including a positive flower structure), (3) at least one Pannonian progradational sequence defined by seismic clinoforms indicating a paleowater depth of approximately 40–80 m, (4) flat spots in several locations of the study area corresponding to possibly biogenic gas in a few hundred meters depth beneath the lake, (5) vertical data wipeouts, which are interpreted as gas chimneys reaching the lake bottom, and (6) definition of the pre-Cenozoic basement. Interestingly, the gas chimneys are interpreted to correspond to the well-known gas seeps (“Kochbrunnen”) in Lake Neusiedl, which were originally described as subaqueous water springs on the lake floor responsible for ice-free areas in the lake ice cover during winter.

scholarly journals Focused Fluid Flow, Shallow Gas Hydrate, and Cold Seep in the Qiongdongnan Basin, Northwestern South China Sea

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Minghui Geng ◽  
Ruwei Zhang ◽  
Shengxiong Yang ◽  
Jun Guo ◽  
Zongheng Chen
Keyword(s):  
Fluid Flow ◽  
South China Sea ◽  
South China ◽  
Gas Hydrate ◽  
Qiongdongnan Basin ◽  
Cold Seep ◽  
Shallow Gas ◽  
Free Gas ◽  
China Sea ◽  
Gas Chimneys

The 3D seismic data acquired in the central Qiongdongnan Basin, northwestern South China Sea, reveal the presence of shallow gas hydrate, free gas, and focused fluid flow in the study area, which are indicated by multiple seismic anomalies, including bottom simulating reflectors, polarity reverses, pulldowns, minor faults, and gas chimneys intensively emplaced within the shallow strata. A new cold seep is also discovered at approximately 1520 m water depths with an ~40 m wide crater in the west part of the study area. Water column imaging, seafloor observation, and sampling using the remotely operated vehicle “Haima” demonstrate ongoing gas seepages and shallow gas hydrates at this site. Thermogenic gas in the study area migrates from the deep reservoir through the gas hydrate stability zone along deep faults and gas chimneys, forms shallow gas hydrate and free gas, and sustains localized gas seepage within this cold seep. The results provide insight into the relationship between shallow gas hydrate accumulation and deep hydrocarbon generation and migration and simultaneously have important implications for hydrocarbon explorations in the Qiongdongnan Basin, northwestern South China Sea.

scholarly journals Optimized Characterization of Gas Chimneys Based on Special Seismic Processing

2019 ◽  
Vol 37 (4) ◽  
Author(s):  
José Paulo Goulart ◽  
David Castro ◽  
Wander Amorim
Keyword(s):  
Seismic Data ◽  
Seismic Signal ◽  
Low Frequencies ◽  
Important Indicator ◽  
Seismic Processing ◽  
Gas Chimney ◽  
Seismic Acquisition ◽  
Seismic Sections ◽  
Gas Chimneys ◽  
Parnaíba Basin

ABSTRACT A new computational methodology was developed to facilitate the interpretation of gas chimneys in seismic sections by analyzing the frequency spectrum of the seismic signal in the Hilbert Domain. Gas chimneys are structures associated with the migration of hydrocarbons or free gas, causing vertical chaotic disturbances in the seismic data. Its occurrence in oil reservoirs is considered an important indicator of the presence of an active petroleum system and its mapping is useful to reduce exploratory risks, increasing the probability of success of the pioneer wells. Standard seismic processing does not favor the recognition of gas chimneys, since their characteristic seismic signature is treated as noise and the low frequencies are strongly attenuated already in the period of the seismic acquisition. The set of reflections is calculated to enhance the low frequencies, making the gas chimneys easily identifiable in the seismic sections where they were not previously even perceived. The special processing flow was applied to seismic data from the Parnaíba Basin “(NE Brazil). This Paleozoic basin is especially rich in gas chimneys, which were favored by transcurrent tectonics associated with the Transbrasiliano Lineament. The gas chimneys interpretation could be validated by the observation of correlated seismic, topographic and geochemical features.KEYWORDS: special processing, gas chimney, exploratory risk, Parnaíba Basin. RESUMO. Uma nova metodologia computacional foi desenvolvida para facilitar a interpretação de chaminés de gás em seções sísmicas por meio da análise do espectro de frequência do sinal sísmico no Domínio de Hilbert. Chaminés de gás são estruturas associadas à migração de hidrocarbonetos ou gás livre, provocando perturbações caóticas verticais no dado sísmico. Sua ocorrência em reservatórios petrolíferos é considerada um importante indicador da presença de um sistema petrolífero ativo e seu mapeamento é útil para reduzir os riscos exploratórios, aumentando a probabilidade de sucesso dos poços pioneiros. O processamento sísmico padrão não favorece o reconhecimento das chaminés de gás, uma vez que a sua assinatura sísmica característica é tratada como ruído e as baixas frequências são fortemente atenuadas já no período da aquisição sísmica. O conjunto de reflexões é calculado para realçar as baixas frequências, tornando as chaminés de gás facilmente identificáveis nas seções sísmicas onde antes não eram nem percebidas. O processamento especial foi aplicado em dados sísmicos da Bacia do Parnaíba. Esta bacia paleozoica é especialmente rica em chaminés de gás, cuja presença foi favorecida pela tectônica transcorrente associada ao Lineamento Transbrasiliano. As chaminés de gás interpretadas puderam também ser validadas pela observação de feições sísmicas, topográficas e geoquímicas correlatas.Palavras-chave: processamento especial, chaminé de gás, risco exploratório, Bacia do Parnaíba.

scholarly journals On low frequencies emitted by air guns at very shallow depths — An experimental study

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. P61-P71 ◽  
Author(s):  
Daniel Wehner ◽  
Martin Landrø ◽  
Lasse Amundsen
Keyword(s):  
Large Volume ◽  
Field Experiments ◽  
Field Measurements ◽  
Seismic Source ◽  
Sea Surface ◽  
Frequency Signal ◽  
Low Frequencies ◽  
Air Gun ◽  
Seismic Acquisition ◽  
Marine Seismic

In marine seismic acquisition, the enhancement of frequency amplitudes below 5 Hz is of special interest because it improves imaging of the subsurface. The frequency content of the air gun, the most commonly used marine seismic source, is mainly controlled by its depth and the volume. Although the depth dependency on frequencies greater than 5 Hz has been thoroughly investigated, for frequencies less than 5 Hz it is less understood. However, recent results suggest that sources fired very close to the sea surface might enhance these very low frequencies. Therefore, we conduct dedicated tank experiments to investigate the changes of the source signal for very shallow sources in more detail. A small-volume air gun is fired at different distances from the water-air interface, including depths for which the air bubble bursts directly into the surrounding air. The variations of the oscillating bubble and surface disturbances, which can cause changes of the reflected signal from the sea surface, are explored to determine whether an increased frequency signal below 5 Hz can be achieved from very shallow air guns. The results are compared with field measurements of a large-volume air gun fired close to the sea surface. The results reveal an increased signal for frequencies below 5 Hz of up to 10 and 20 dB for the tank and field experiments, respectively, for the source depth at which the air gun bubble bursts directly into the surrounding air. For large-volume air guns, an increased low-frequency signal might also be achieved for sources that are slightly deeper than this bursting depth. From these observations, new design considerations in the geometry of air-gun arrays in marine seismic acquisition are suggested.

Innovative seismic imaging of VMS deposits, Neves-Corvo, Portugal: Part I - In-mine array

Geophysics ◽  
2021 ◽  
pp. 1-76
Author(s):  
Bojan Brodic ◽  
Alireza Malehmir ◽  
Nelson Bruno Monteiro Pacheco ◽  
Christopher Juhlin ◽  
Joao Carvalho ◽  
...  
Keyword(s):  
Seismic Imaging ◽  
Ground Surface ◽  
Seismic Source ◽  
Massive Sulfide ◽  
Seismic Profiles ◽  
Time Migration ◽  
Active Source ◽  
Seismic Experiment ◽  
Rock Mining ◽  
Seismic Acquisition

To evaluate and upscale the feasibility of utilizing exploration tunnels in an operating mine for active-source seismic imaging, a seismic experiment was conducted at the Neves-Corvo mine, in southern Portugal. Four seismic profiles were deployed in exploration drifts ca. 650 m beneath the ground surface, above the world-class Lombador volcanogenic massive sulfide (VMS) deposit. In addition to the tunnel profiles, two perpendicular surface seismic profiles were deployed above the exploration tunnels. The survey was possible due to a newly developed prototype GPS-time transmitter enabling accurate GPS synchronization of cabled and nodal seismic recorders, both below and on the surface. Another innovative acquisition aspect was a 1.65 t broadband, linear synchronous motor (LSM) driven - electric seismic vibrator (e-vib) used as the seismic source along two of the exploration tunnels. Challenges and innovations necessary for active-source tunnel seismic acquisition, characterized by high levels of vibrational noise from the mining activities, are discussed. Additionally, the LSM vibrator’s signal and overall seismic data quality in this hard rock mining environment are evaluated. Processing results from the tunnel data and 3D reflection imaging of the Lombador deposit below the exploration tunnels are shown and the results checked for consistency through constant-velocity 3D ray-tracing traveltime forward modeling. For imaging purposes, 3D Kirchhoff pre-stack depth and post-stack time migration algorithms were used, with both successfully imaging the targeted deposit. The results obtained show that active-source seismic imaging using subsurface mining infrastructure of operational mines is possible. However, it requires innovative exploration strategies, a broadband seismic source, an accurate GPS-time system capable of transmitting GPS-time hundreds of meters below the surface and careful processing. The results obtained open up possibilities for similar studies in different mining or tunneling projects.

scholarly journals THIN BED IDENTIFICATION IMPROVEMENT USING SHORT – TIME FOURIER TRANSFORM HALF – CEPSTRUM ON “TG” FIELD

PETRO ◽  
2019 ◽  
Vol 8 (3) ◽  
pp. 103
Author(s):  
Intan Andriani Putri ◽  
Awali Priyono
Keyword(s):  
Fourier Transform ◽  
Seismic Data ◽  
Acoustic Impedance ◽  
Resolution Enhancement ◽  
Frequency Component ◽  
Advanced Technology ◽  
High Frequency Component ◽  
Short Time Fourier Transform ◽  
Seismic Acquisition ◽  
Short Time

<p>Thin Bed Identification is still a difficult task even with the advanced technology of seismic acquisition. Certain high frequency component is necessary and could be obtained through resolution enhancement. Short – Time Fourier Transform Half Cepstrum (STFTHC) is performed to enhance seismic resolution thus a better separation of thin bed could be improved. Basic principal of STFTHC is to replace the frequency spectrum by its logarithm while phase spectrum remains the same. Synthetic seismic was built based on Ricker and Rayleigh criterion. They were used to test the program yielding a better separation of two interfaces under tuning thickness without creating new artifacts. The algorithm was applied to seismic data from TG field. Using post-STFTHC seismic data as input of acoustic impedance inversion, well tie correlation increases by 10% and decreases inversion analysis error by 17,5%. Several thin bed -which once could not- could be identified on acoustic impedance result.</p>

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