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Book Chapter

Amplitude Anomalies in a Sequence Stratigraphic Framework: Exploration Successes and Pitfalls in a Subgorge Play, Sacramento Basin, California

By
Jeffrey A. May
Jeffrey A. May
EOG Resources, Inc. (formerly at DDD Energy, Inc.) 600 17th Street, Suite 1100N Denver, Colorado 80120
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Mark S. Przywara
Mark S. Przywara
DDD Energy, Inc. 50 Briar Hollow Lane, 7th Floor West Houston, Texas 77027
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Thomas A. Mazza
Thomas A. Mazza
Deceased (formerly at DDD Energy, Inc.)
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Ruble Clark
Ruble Clark
Yuma Exploration & Production Co. (formerly at DDD Energy, Inc.) 1177 West Loop South, Suite 1825 Houston, Texas 77027
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John Dlouhy
John Dlouhy
OXY U.S.A., Inc. P.O. Box 1002 Tupman, California 93276-1002
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Roger Hettenhausen
Roger Hettenhausen
OXY U.S.A., Inc. P.O. Box 1002 Tupman, California 93276-1002
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Published:
December 01, 2002

Abstract

The Sacramento Basin is part of the Great Valley, a prolific hydrocarbon province that is the remnant of a Late Mesozoic-Early Cenozoic forearc basin in California. A series of buried submarine canyons extend seaward from the eastern margin of the forearc. These “gorges” have formed during multiple episodes of relative sea-level fall during the Tertiary, truncating Late Cretaceous through Eocene marine and nonmarine sandstones. Mudstones dominate the canyon fill, creating lateral and top seals for numerous gas reservoirs.

The late Paleocene Meganos Gorge crosses a proprietary three-dimensional (3-D) seismic survey where DDD Energy and OXY U.S.A. jointly have drilled numerous gas discoveries. Five discoveries occur in fluvial-deltaic sandstones of the Maestrichtian Mokelumne River Formation from traps beneath the Meganos Gorge, a configuration with which we have had 100% success. The key to this success is understanding the associated amplitude anomalies within their sequence stratigraphic and lithologic context.

Initially, we (1) identified all amplitude anomalies, (2) mapped the base Meganos Gorge sequence boundary, and (3) mapped regional flooding surfaces within the highstand Mokelumne River section, paying particular attention to truncations beneath the sequence boundary. Two gas fields in the area are analogs for subcrop production from the Mokelumne River: McDonald Island Field (now used for gas storage), which has an estimated ultimate recovery (EUR) of ~184 billion cubic feet (bcf) of gas, and King Island Field, which has a EUR of ~11 bcf.

We next conducted amplitude-versus-offset (AVO) analyses for all lithologies that yield anomalously high amplitude signatures. We built a database for lignites, low-velocity mudstones, carbonate-cemented sandstones, and conglomerates, in addition to gas-charged sandstones. Finally, we risked our subgorge prospects based on AVO response, structural position relative to the canyon-base sequence boundary, and juxtaposition of lithologies across the sequence boundary. The analytical steps used here can be applied to the continued discovery of subcrop reservoirs associated with other gorges in the Sacramento Basin, as well as the search for hydrocarbons trapped beneath submarine canyons in deep-water basins worldwide.

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Contents

GCSSEPM

Sequence Stratigraphic Models for Exploration and Production: Evolving Methodology, Emerging Models and Application Histories

John M. Armentrout
John M. Armentrout
Houston, Texas
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Norman C. Rosen
Norman C. Rosen
Houston, Texas
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SEPM Society for Sedimentary Geology
Volume
22
ISBN electronic:
978-0-9836096-8-1
Publication date:
December 01, 2002

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