Apresentações/ Eventos

2022 Ocean Sciences Meeting

Realizado de 24 de fevereiro à 4 de março de 2022, o Ocean Sciences Meeting contou com a participação do membro do projeto Francisco Carlos Lajús Junior, o qual apresentou seu trabalho entitulado A possible seismic oceanography signature in ocean bottom nodes data. Abaixo segue o vídeo da apresentação. Mais informações sobre o evento se encontra na sua página oficial.

TÍTULO: A possible seismic oceanography signature in ocean bottom nodes data

AUTORES: Francisco Carlos Lajús Junior, Yasmim Mourad Oshiro, André Bulcão, Antonio Henrique da Fontoura Klein.

RESUMO: Seismic imaging using ship-towed acoustic sources and deployed ocean bottom nodes is one of many possible techniques adopted by the oil companies for exploring earth structure beneath the oceans, with increased imaging detail. For that, one makes use of the acoustic field separation, into downgoing and upgoing wave fields, where typically the latter is mostly focused for geological surveys. By accessing a fraction of the downgoing wave-field, however, some acoustic events appear to be associated with reflections occurring in the water layer, thus raising the possibility that perhaps secondary reflection back propagates downward from the sea surface, to the node position. Solutions obtained by a synthetic wave-propagation model are here investigated under this modeling assumption, which are later used with application of interferometric principles, in order to redatum the wave-field as a surface reflection acquisition geometry. If such behavior is confirmed in practice, it might be useful in the development of more detailed water velocity corrections that depart strictly from their underlying signature on the transmitted arrivals in ocean bottom receivers.

17th International Congress of the Brazilian Geophysical Society

De 8 à 11 de novembro aconteceu, de forma online, o 17th International Congress of the Brazilian Geophysical Society. Neste evento, participantes do projeto Velocidade do Som apresentaram resultados de seus respectivos trabalhos. Os trabalhos seguem abaixo. Mais informações sobre o evento se encontra na sua página oficial.

TÍTULO: The structure of water-layer sensitivity kernels in OBN-type acquisition geometries

AUTORES: Francisco Carlos Lajús Junior, Antonio Henrique da Fontoura Klein.

RESUMO: The water column is usually taken as an homogeneous velocity layer in OBN-type marine seismic surveys. Heterogeneities caused by salinity and temperature variations, however, may introduce significant artifacts resulting in inaccurate interpretation of sub-sea floor geologic features, especially accounting the long time spans of seismic acquisitions that take place in ultra-deep ocean environments. Here we investigate the underlying structure of sensitivity kernels in this horizontally distributed acquisition geometry, mostly focused on the development of improved water layer velocity reconstructions from bottom node data. Two possible formulations are here considered, relating first arrivals with velocity perturbations, where a reference oceanic state and some overall shape/pattern of the velocity perturbations could be known a priori. The results are expected to provide guidelines for adapted inversion schemes, directed to more detailed water layer velocity reconstruction.

TÍTULO: Waveform-preserving processing flow of multichannel seismic reflection data for ocean thermohaline structure reconstruction (revisited)

AUTORES: Josafat Ribeiro Leal Filho, Francisco Carlos Lajus. Junior, Antonio Henrique da Fontoura Klein, Stephan Paul.

RESUMO: Along with the advent of 4D seismic exploration, the need to properly compensate for spatio-temporal variations in the water column has become of utterly importance for the adequate characterization of reservoir changes during their exploration phase. In this study we revisit a previously suggested processing flow that is focused on the recovery of oceanographic coherent structures (DAGNINO et al.,2017), and propose some modifications. The main reason for this is our restriction to work with already processed (by 3rd parties) data, which was mostly guided to proper characterization of sub-sea floor geologic structures. We found that our re-processing flow is able to recover signatures of oceanic thermohaline structures, thus having a potential for further inversion focused on detailed water layer velocity reconstruction.

TÍTULO: Sound speed spatial and temporal variability in Campos and Santos Basins and its influence on traveltime

AUTORES: Pedro Lins de Souza, Antonio Fernando Härter Fetter Filho e Francisco Carlos Lajús Junior.

RESUMO: Sound speed (SS) variability in the oceans, if not taken into account, can negatively impact seismic imaging, especially in ultradeep locations (>2000m) such as the hydrocarbon reserves in the Campos and Santos Basins pre-salt region. The current work describes the variability of sound speed on the basins area derived from three reanalysis products: Oras-ECMWF, GLORYS12V1 and Hycom Gofs 3.0. The impact of SS variability on the oceanic region of Santos Basin was also addressed. The model data evaluation with in situ ARGO profiles indicated smaller prediction errors on GLORYS results. The sound speed variability was investigated with EOF analysis that revealed a small positive linear trend for the central and intermediate layer for ORAS and GLORYS and a spatial pattern of north-south dipole on the second mode. On the oceanic region of Santos Basin the reanalysis profiles agreed reasonably well and presented negative and positive anomalies at interannual scales that caused deviations in traveltime up to 10−3s.


TÍTULO: On the application of Fermat’s interferometric principle for water-layer velocity reconstruction in OBN data

AUTORES: Yasmim Mourad Oshiro, Francisco Carlos Lajus Junior, Sherif Mahmoud Hanafy, Gerard Thomas Schuster, Carlos Eduardo Theodoro, Antonio Henrique da Fontoura Klein.

RESUMO: Knowledge of sea water velocity variations is an important issue for subsurface seismic imaging, particularly in 3D and 4D surveys where reservoir variations must be distinguished from those related to spatio-temporal water variations. A very promisingly and highly-resolved alternative to classical water velocity corrections involves the processing of small amplitude reflections observed within the water layer, during typical marine acquisitions with streamers. In this study we investigate the possibility that these very same reflections could be sensed by Ocean Bottom Nodes (OBN), thus helping the development of more detailed water velocity reconstruction for the transmitted arrivals. For that, first we  conduct synthetic simulations to obtain the propagated acoustic field, enforcing our focus on its down-going components. Once such water reflections (now transmitted down to OBN location) are identified in the generated responses, some form of Fermat’s interferometric redatum can be applied. It is found that such information might be helpful on the development of more detailed water velocity corrections departed strictly from their underlying signature on the transmitted arrivals.

TÍTULO: Parameterized water layer reconstruction for first arrivals in OBN data

AUTORES: Lucas Fragoso Vale Paiva, Francisco Carlos Lajus Jr., André Bulcão, Bruno Dias, Antonio Henrique da Fontoura Klein.

RESUMO: In this work we present current results for an ongoing formulation of an inversion method focused on water velocity reconstruction of Ocean Bottom Nodes (OBN) data, based strictly on the varying behavior of first arrivals with the source offset distance. Given the similarities with the field of Oceanic Acoustic Tomography (OAT), some typical assumptions applied to the acoustic propagation on the ocean environment, such as the linearized disturbances of the sound velocity, are here enforced. Additionally, two sets of available oceanographic information, that can be known a priori for a certain region of interest, are considered: 1) monthly-averaged sound velocity profiles from reanalysis models, and 2) a parameterized set of modes to describe velocity disturbances. Our results are verified to provide improved water velocity reconstructions over a vertically homogeneous profile, which is typically considered in geophysical imaging.