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 proposed an additional approach to investigate gas hydrate occurrences in the Foz do Amazonas Basin, in the Brazilian Equatorial Margin. The automatic comparison of seafloor seismic amplitudes with those from the Bottom Simulating Reflectors (BSR) was used to exhibit the reversal of signal polarities among the seafloor (positive) and the BSR (negative), reinforcing the identification of BSR in areas where its visualization was unclear. Additionally, we used the envelope attribute to highlight the BSR in the seismic section. Subsequently, we decomposed the seismic data into different frequency bands, applied a -90 degrees phase rotation to the data and recalculated the envelope attribute for each section decomposed in frequency bands. This technique improved visualization, allowing the identification of intervals where BSR were laterally discontinuous, revealing to be valuable for mapping the gas hydrate distribution in Foz do Amazonas Basin.
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.
The venue was a very good one. Its location was well-suited for easy walks to nearby restaurants; the meeting room was well-equipped and a good size for hosting the attendees; and having everyone stay at the same hotel made it conducive to fostering conversations with others outside of the main presentations, which is often where some of the most useful discussions take place.• II PANGEO was successful because of the number of participants from different countries, and because of the large number of students in attendance. I believe that the students found it very valuable to learn from more senior scientists and to exchange ideas with them.• The range of topics presented at the workshop was very good, covering a variety of areas of expertise. Suggestions (for III PANGEO):• I would recommend trying to schedule more time for hands-on measurement sessions at the observatory. If people are encouraged to bring their own theodolites to the workshop, they should have more opportunity to work with experienced observers who can advise them on their techniques and methods of recording their absolute measurements.• I would encourage more time for hands-on equipment sessions, or demonstrations of software that can be used to view, analyze, or process data. I think this is one of the most important ways we can build capacity in other countries who may not have the means to develop such tools themselves.• All of the attendees would benefit from having the full workshop schedule available to them before traveling to the workshop, so that they can plan their travel and presentations accordingly.
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