The Use of CSEM within an Integrated Exploration Project "Best of EAGE"
Lovatini, Andrea 1; Medina, Elena 1;
Campbell, Tracy 2; Myers, Keith 3
(1)Integrated EM
Center of Excellence, WesternGeco, Milan, Italy. (2) WesternGeco, Baku,
Azerbaijan. (3) WesternGeco, Perth, WA, Australia.
We discuss the integration of multiple geophysical methods in a single project basin study in the offshore Potiguar basin, located in northeastern Brazil, where there is production from the nearshore area, but no production and limited exploration from the deepwater portion.
The existing 2D seismic dataset, initially available only as
prestack time migrated data, underwent prestack depth
migration using new tools
for noise attenuation and multiple removal. The results showed significant
spectral content improvement at shallow depths and fault and reflector
definition and continuity in the deeper section. The dataset was interpreted to
provide regional scale horizons and used as input with other geological and
geochemical data for a petroleum system model of the whole basin. Satellite
images were processed to provide a map of sea-surface oil slicks.
The CSEM method was applied at a different stage than its more
common utilization in exploration workflows, which is as a tool to evaluate
known prospects. It was applied together with other methods to provide further
information on the geology of a poorly explored basin. Oil slicks and seismic
interpretation structural and stratigraphic features were used to identify
possible areas for CSEM acquisition. 1D modeling
was preliminarily used to
identify which features were detectable. Approximately twelve targets were
prioritized using the 1D
modeling
results, their seismic characteristics, their
level of complexity for CSEM interpretation and also their areal distribution
within the entire basin. 2.5D and 3D
modeling
was used to investigate more
complex targets. To cover as broad a range of depths as possible, a spectrum
with high energy at multiple frequencies was designed.
To include as many targets as possible in the basin in a
cost-efficient way, without losing 3D illumination, a hybrid approach between
2D and 3D layouts was followed in survey design.
Within the basin five separate datasets were acquired. The
interpretation workflow included: qualitative interpretation; 1D anisotropic
inversions; up-scaling to 2D and 3D resistivity volumes; background model
forward modeling
assessment; 2.5D and then 3D anisotropic inversions. All the
3D inversions used multiple frequencies to improve both sensitivity and
resolution.
The resistivity volumes were then integrated with the seismic
data, the interpreted horizons, the oil-slicks and the petroleum system
modeling
predicted accumulations in a single 3D
earth
model.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.