Banca de DEFESA: ALEX TITO DE OLIVEIRA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : ALEX TITO DE OLIVEIRA
DATA : 17/12/2018
HORA: 09:00
LOCAL: Auditório do Departamento de Geofísica
TÍTULO:

Can full waveform inversion compensate for the lack of illumination in crosswell tomography? 

PALAVRAS-CHAVES:

Full waveform inversion; crosswell tomography; seismic tomography

PÁGINAS: 85
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:

Seismic illumination at each point of the interwell region can be defined as the maximum angle between the rays that pass through the point. Interfaces completely contained in the angular apertures can be imaged with first arrival travel time tomography (FATTT), but interfaces completely outside cannot be imaged even under regularized FATTT. We investigate if 2D acoustic full waveform inversion (FWI) can compensate for the lack of illumination. We use synthetic data generated with Ricker source wavelets with peak frequencies at 100 or 500 Hz, resulting in a small overlapping in the frequency bandwidths, so that a multiscale FWI approach is employed where the results with the 100 Hz dataset are used as input for the 500 Hz dataset. We investigate two FWI cases: in the first (FWI T), just the waves recorded at the opposite borehole are used whilst, in the second case (FWI T+R), the waves recorded at the two boreholes are used. For a single interface separating two media, the shape of the transmitted waveform varies significantly only when the interface is contained in the angular apertures. Accordingly, shot gathers for layered models with interfaces outside the angular apertures can be approximately reproduced with equivalent homogeneous media. As a result, in comparison with FATTT, both FWI cases give a mild improvement for models with interfaces inside the angular coverage, but cannot compensate for the lack of illumination. In this situation, minor resolution increases are obtained either with FWI T or FWI T+R cases. However, for models in the mixed condition where layers with interfaces inside the angular coverage are cut by a fault, FWI offers substantial improvements over FATTT, even if the fault plane is outside the angular coverage and FWI T is employed. In this mixed situation, resolution also increases when FWI T+R and source wavelets with a higher frequency content are used.

MEMBROS DA BANCA:
Interno - 1451214 - ADERSON FARIAS DO NASCIMENTO
Externo à Instituição - AMIN BASSREI - UFBA
Presidente - 349684 - WALTER EUGENIO DE MEDEIROS