Banca de DEFESA: VICTÓRIA MARIA DE ALMEIDA SANTOS CEDRAZ

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : VICTÓRIA MARIA DE ALMEIDA SANTOS CEDRAZ
DATE: 15/05/2024
TIME: 09:00
LOCAL: Videoconferência / Canal Youtube PPGG
TITLE:

Characterization of dispersive effects in GPR data caused by deformation bands in
sandstones: Petrophysics, numerical modeling and multi-attribute analysis

KEY WORDS:

Deformation bands; brittle deformation; siliciclastic rocks, Electromagnetic dispersion; Complex
dielectric constant; GPR modeling; GPR attributes; architecture of deformation bands

PAGES: 102
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geofísica
SPECIALTY: Geofísica Aplicada
SUMMARY:

We assessed the impact of deformation bands (DBs) on Ground-Penetrating Radar (GPR)
data in a siliciclastic sandstone reservoir analog scenario. To achieve this goal, we employed
an integrated and multidisciplinary approach in two stages. First, we present both laboratory
and modeling results supporting the fact that DBs contained in siliciclastic rocks can be
detected as narrow zones of attenuated signal in GPR images. Measurements of complex
dielectric constant of clean sandstones (frequency range 50-400 MHz) show that values of
quality factor (Q) are strongly influenced by grain size: Q value decreases with decreasing
grain size. Therefore, DBs are associated with relatively low Q values because they always
cause grain reduction in comparison with host rock. In addition, two-dimensional GPR
modeling, including dispersive effects caused by DBs, shows that they appear indeed as
narrow zones of attenuated signal in two cases: a conceptual cluster of DBs contained in a
layer-cake model and an approximate reproduction of a field image. In both cases, DBs were
modeled as zones of relatively low Q values, allowing their detection by dispersive effects.
Laboratory measurements also reveal that the constant-Q model becomes a better
approximation as Q values decrease. Due to the fact that the influence of Q is really important
when its value is low, this result supports the use of the Q-constant model for modeling
radargrams including dispersive effects. The second approach of this research consisted of
explore the possibility to map DBs through GPR since they cannot be imaged by seismic
methods. Although DBs and host rocks share the same lithology, GPR imaging is possible
because DBs can cause small vertical offsets and reduce the amplitude of the GPR signal. We
present an automatic approach to extract the three-dimensional (3D) architecture of DBs from
GPR cubes using multi-attribute analysis. We used a 200 MHz GPR cube surveyed on an
outcrop of a sandstone formation highly impacted by DBs in the Rio do Peixe Basin,
Northeastern Brazil. The multi-attribute analysis is based on edge evidence and sequential
ant-tracking, a combination that can identify narrow zones of attenuated GPR signal.
Furthermore, the 3D architecture of DBs was extracted as a geobody using an opacity
balancing operator. The geological reliability and limitations of the geobody is demonstrated by
comparing slices of it with photographs of exposed DBs in similar positioning, in addition to structural measurements obtained in field and in the geobody.

COMMITTEE MEMBERS:
Interno - ***.785.944-** - VINCENZO LA BRUNA - NÃO INFORMADO
Interno - 349684 - WALTER EUGENIO DE MEDEIROS
Externo à Instituição - JESSÉ CARVALHO COSTA - UFPA
Externo à Instituição - MICHAEL STRUGALE - PETROBRAS
Externo à Instituição - WAGNER MOREIRA LUPINACCI - UFF