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Book Chapter

Gulf of Mexico “Bright Spots”: Early Shell Discoveries

By
Michael C. Forrest
Michael C. Forrest
Consultant (Shell Oil Company, Retired), Dallas, Texas, U.S.A.
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Published:
January 01, 2005

ABSTRACT

During June 1967, the author observed a strong seismic reflection, with attenuation below the event, at a depth of 3000 ft (910 m) on the crest of a low-relief structure in Main Pass area, offshore Louisiana. The most likely interpretation was that a calcareous zone, a “hard streak,” caused the strong reflection. Later, two exploration wells penetrated the shallow reflection and found a 25-ft (9 m) gas pay with very low sonic log velocity; a “soft” reflection. Also, an amplitude anomaly in the south Timbalier area with about 2500 ft (760 m) of relief at a depth of 12,000 ft (3660 m) was observed to be associated with a thick oil sand.

During 1968 and early 1969, strong seismic reflections were observed on exploration prospects in the offshore Texas and Louisiana Pleistocene trend. Digital acquisition and processing preserved the relative amplitudes of seismic data in contrast to automatic gain control. The term “bright spot” was coined during informal discussions. Seismic was primarily used to map structure at that time, and most geoscientists doubted the relationship of “bright spots” to gas/oil pays. During mid-1969, six oil and gas fields were studied in the offshore Louisiana Pliocene trend, and observed “bright spots” were correlated with gas sands that had a very low sonic log velocity. Shell management formed an operations/research team to study seismic amplitude changes related to gas and oil pays.

The first significant application of “bright spot” technology was in 1970 when Shell technical staff predicted the thickness of a gas sand and mapped other pays on Eugene Island Block 331 (150 million bbl of oil equivalent). During 1972, Shell predicted oil pays in the discovery of South Marsh Island 130 Field (250 million bbl of oil equivalent). Many other discoveries followed, especially Cognac in deep water.

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Contents

AAPG Special Publication

Discoverers of the 20th Century: Perfecting the Search

Charles A. Sternbach
Charles A. Sternbach
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Marlan W. Downey
Marlan W. Downey
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Gerald M. Friedman
Gerald M. Friedman
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American Association of Petroleum Geologists
Volume
1
ISBN electronic:
9781629810409
Publication date:
January 01, 2005

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