Banca de DEFESA: EDWIN HUMBERTO FAGUA DUARTE

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : EDWIN HUMBERTO FAGUA DUARTE
DATE: 21/10/2021
TIME: 14:00
LOCAL: Plataforma Google Meet
TITLE:

Optimized methods for Full Waveform Inversion in 3D

KEY WORDS:

Full Waveform Inversion, Simultaneous sources, encoding strategies, inversion using 3D field data.

PAGES: 73
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

Full waveform inversion (FWI) is one of the most studied techniques today to recover subsurface parameters that affect
wave propagation. One of the main difficulties in applying FWI in 3D seismic surveys is its high computational cost. This
problem has been solved with the advancement of computational technology, but there are still difficulties to apply a FWI to real
3D data. In this work are studied implemented to optimize a FWI, as which are based on the physical properties of waves. To
this end, this work was done in two parts. In the first part, the encoded simultaneous sources technique was used, in which the
FWI gradient is calculated by simultaneously propagating information from several sources grouped in one or several subgroups,
taking advantage of the superposition principle of the wave equation. In order to reduce the crosstalk noise that appears in the
gradient calculation using simultaneous sources, two encoding schemes have been proposed, by phase rotation and by static
limited to a period of the dominant frequency. In phase rotation encoding a phase rotation is applied to each shot where the
rotation angle is chosen randomly for each shot. In static coding the traces of each shot are temporally shifted and the value of
this shift is chosen randomly for each shot having a maximum value of one period of the dominant frequency of the data. With
the help of numerical tests on synthetic 2D data to demonstrate that the proposed schemes have a faster convergence than
encodings by polarization (multiply by +1 or -1 randomly each shot) and by static without being limited. In the second part, a
workflow was developed to apply a FWI to real data acquired in the Brazilian pre-salt region. This data was obtained with an
Ocean Bottom Node (OBN) 3D acquisition, where the receivers are spread at the ocean bottom. In the developed workflow,
several existing techniques are combined to optimize the use of memory and processing, which take advantage of wave
propagation properties. On the OBN data for inversions made using sources and receivers decimation strategies to reduce
computational cost. The encoded source schemes studied in the first part were also tested. These testicles also use various
functions with the objective of an intention of melody and a resolution of inversions. It was verified that the inversions recovered
information related to the pre-salt reservoir and that both decimation and source coding strategies reduced the computational cost
of FWI without compromising the quality of the inversion.

BANKING MEMBERS:
Interno - 1345774 - CLAUDIONOR GOMES BEZERRA
Interno - 1379465 - GILBERTO CORSO
Externo à Instituição - JESSÉ CARVALHO COSTA - UFPA
Interno - 2492756 - JOAO MEDEIROS DE ARAUJO
Externo à Instituição - JORGE LUIS LOPEZ
Externo à Instituição - REYNAM DA CRUZ PESTANA - UFBA