Historically, marine research has been using single-channel seismic (SCS) devices for scientific projects. Despite SCS’s abundant data availability and the contribution it has brought for subsurface comprehension, few efforts have been dedicated to improve the SCS processing flow to extract more information carried by seismic signals and for better imaging. Diffractions present the necessary means to estimate sediment acoustic properties useful for imaging, stability studies, and geohazard prevention. The root-mean-square (rms) velocity is estimated from diffractions using a diffraction velocity analysis workflow composed of the following main steps: separation of diffractions from specular events using stationary phase properties and plane-wave destruction filtering, determination of diffractor locations in time, velocity scanning using constant rms velocity time migration, automatic picking of rms velocity at the diffractor location in the scan volume, and quality control to avoid spurious rms velocity. The method circumvents the sparsity and nonuniform distribution of diffractions for smooth lateral velocity change conditions. Application in a SCS line acquired in the Joetsu Basin, Japan Sea, indicates improvement in the focusing of deeper events compared to the previous processing flow, and it adds consistent information about the acoustic properties of the subsurface.
ABSTRACT. Foz do Amazonas basin is located at the northern portion of the Brazilian Equatorial Margin, along the coastal zone of Amapá and Pará states. This basin has been subjected to several studies, and the presence of gas hydrates has been demonstrated locally through sampling, and over broader areas using seismic reflection data. Seismic reflection is one method to identify the occurrence of gas hydrates, as they give rise to well-marked reflectors that simulate the seafloor, known as Bottom Simulating Reflectors (BSR). This study aims to investigate BSRs associated with the presence of methane hydrates in the Foz do Amazonas Basin through the application of seismic attributes. It was compared seismic amplitudes from the seafloor and the BSR to validate the inferred seismic feature. Then, Envelope and Second Derivative were chosen for highlighting the BSR in seismic section. The results showed an inversion of polarities in the signal between the seafloor (positive polarity) and the BSR (negative polarity). The integrated use of these approaches allowed validating the level of the BSR in line 0239-0035 and inferring the presence of gas hydrates, revealing to be a useful tool for interpreting the distribution of the gas hydrates in the Foz do Amazonas Basin.Keywords: Gas hydrates, envelope, second derivative of envelope, Brazilian Equatorial Margin.RESUMO. A Bacia da Foz do Amazonas é localizada na porção norte da Margem Equatorial Brasileira, ao longo da zona de costa dos estados do Amapá e do Pará. A presença de hidratos de gás é comprovada localmente através de amostragem, e em áreas mais distantes através de dados de sísmica de reflexão. A sísmica de reflexão é eficaz para identificar hidratos de gás, pois refletores que simulam o fundo do mar, Bottom Simulating Reflectors (BSR), são utilizados para inferir a presença dos hidratos de metano. Este estudo pretende identificar feições sísmicas associadas aos hidratos de metano na Bacia da Foz do Amazonas através da aplicação de atributos sísmicos. Foram comparadas as amplitudes sísmicas do fundo do mar e do BSR para validar a feição sísmica inferida. Então, os atributos Envelope e Segunda Derivada do Envelope foram escolhidos por destacarem o BSR. Os resultados mostraram uma inversão das polaridades no sinal entre o fundo do mar (positivo) e o BSR (negativo). O uso integrado dessas abordagens valida a localização do BSR na linha 0239-0035 e infere a ocorrência de hidratos de gás, revelando ser uma ferramenta útil para interpretação da distribuição de hidratos de gás na Bacia da Foz do Amazonas.Palavras-chave: Hidratos de metano, envelope, segunda derivada do envelope, Margem Equatorial Brasileira.
This work aims to evaluate the best seismic attributes to use to identify the Bottom Simulating Reflector (BSR) of Umitaka Spur, a well-known gas hydrate area in Joetsu Basin, Japan. For this purpose, it uses 2D single-channel seismic data from cruises NT07-20 and NT08-09 provided by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The methodology used for the qualitative analysis of six seismic attributes to highlight the BSR was done using Schlumberger’s Petrel software. These attributes were Envelope, RMS Amplitude, Amplitude Volume Technique (tecVA), Relative Acoustic Impedance, Spectral Decomposition and Instantaneous Frequency. Thus, this study was fundamental to investigate gas hydrates occurrence through the seismic assessment of some geophysical property (amplitude and frequency) and the geological attributes that highlighted the faults of the complex local geology. The application of these attributes can be used in other areas providing an effective tool to enhance the recognition of BSR all over the world.
This work aims to evaluate the best seismic attributes for identifying the BSRs of Umitaka Spur, a well-known gas hydrates field, from the Joetsu Basin, Japan. For this purpose, it uses 2D single-channel seismic data from Expeditions NT07-20 and NT08-09 made available by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The methodology consisted of the analysis of six seismic attributes to highlight the Bottom Simulating Reflectors (BSRs), through Schlumberger's Petrel 2019 software. These attributes were Envelope, RMS Amplitude, Amplitude Volume Technique, Relative Acoustic Impedance, Spectral Decomposition and Instantaneous Frequency. Thus, this methodology was fundamental to reduce the ambiguities inherent to geophysics, by highlighting the real BSRs through the seismic assessment of more than one physical property (amplitude and frequency) and the geological attributes that highlighted the faults of the complex local geology.
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