--> Merging Geology and Geophysics with Emerging Techniques in Subsalt Imaging, Lewis, Jennifer L.; Eisenberg, Richard; Blumenthal, Errol, #90100 (2009)

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Merging Geology and Geophysics with Emerging Techniques in Subsalt Imaging

Lewis, Jennifer L.1
 Eisenberg, Richard2
 Blumenthal, Errol3

1Energy Technology Company, Chevron, Houston, TX.
2
Latin
America Business Unit, Chevron, Houston, TX.
3
North
America Exploration and Production, Chevron, Houston, TX.

For decades, the postsalt heavy oil fields in the Espirito, Campos and Santos Basins, along with a few presalt heavy oil fields in the nearshore Campos, supported the exploration and production program of offshore Brazil. The 2007 Tupi discovery in the Santos was the first significant presalt find in offshore Brazil, with recoverable reserves estimated to be as high as 5-7 billion barrels of light oil. With the transition from exploration to appraisal and development comes the need for improved and more accurate subsurface characterization. Salt, often many thousands of meters thick, such as that found in the canopies of the Gulf of Mexico and the autochthonous salt layer of Brazil, provide numerous challenges from drilling and reservoir management to seismic imaging.


Presalt seismic data are notorious for their low frequency content, multiple contamination, and poorly constrained velocities. These limitations make characterization of key reservoir uncertainties, such as faulting, compartmentalization and overall structural geometry, an onerous undertaking at best. Accurate characterization of uncertainties such as these play a prominent role in determining well placement and well count, which are factors that impact ultimate recovery, development scenarios and project economics. In a setting where wells are sparse and expensive to drill and complete, better seismic leads to better decisions.


Recently, industry has recognized step-change improvements in subsurface imaging in deepwater subsalt settings, particularly in the
Gulf of Mexico, with advances such as wide-azimuth acquisition, reverse time migration, and interactive prestack depth migration. The labels and algorithms are impressive, but the real success of many of these geophysical techniques not only requires but is directed by geologic insight. A higher quality subsalt image, driven by a union of geology and geophysics, can contribute to a clearer understanding of critical risks and uncertainties.


AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil