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GCSeismic
Meta-Attributes as a Practical Exploration Tool: Gas Chimney and Fault
Volumes*
By
Fred Aminzadeh1 and David Connolly1
Search and Discovery Article #40101 (2003)
*Adapted for online presentation from the Geophysical Corner column in AAPG Explorer December, 2002, entitled “Looking For Gas Chimneys And Faults,” prepared by the authors. Appreciation is expressed to the authors, to R. Randy Ray, Chairman of the AAPG Geophysical Integration Committee, and to Larry Nation, AAPG Communications Director, for their support of this online version.
1dGB-USA, Houston, Texas (www.dgbusa.com; [email protected])
Introduction
Gas chimney and fault
volumes extracted from 3-D seismic data are rapidly
becoming valuable tools for exploration and field development. Various seismic
anomalies such as chimneys, faults, fractures, salt and sand bodies can be
highlighted using a new technique that analyzes data with combinations of
seismic attributes.
This article focuses on the mapping of gas chimneys and faults.
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New Type of Seismic Volumes
Chimney cubes (Figure 1) and
Current applications of chimney and
Computers can be trained to search through data volumes looking for seismic objects, using carefully designed criteria “meta-attributes,” which are an aggregation of a number of seismic attributes where the interpreter’s insight is combined with the power of a trained neural network to detect a particular seismic anomaly.
As shown in Figure 3, a multitude of attributes from known or suspected
chimneys (or faults) are used as input to a neural network. Training of
the neural network using interpreter’s insight renders the
“meta-attribute” suitable for detection of a given seismic body, like
gas chimneys or
Gas ChimneyFigure 1 shows a typical gas chimney in yellow overlaid on a deep salt structure with deep and shallow reservoir units. It highlights the migration pathway of hydrocarbon from deep structures into shallower reservoirs and into near surface gas pockets. Gas clouds and gas chimneys have often been considered as a source of seismic noise that degrades the quality of seismic reflection events. Much effort has been devoted to filter out the impact of gas clouds and provide interpretable sections by imaging through them. Our main focus, however, is to highlight such events and establish a link between chimney characteristics (occurrence, type and extent) and geologic concepts critical for successful exploration. For example, mapping the location and origination/termination points of gas chimneys helps the:
Sometimes it is difficult to pinpoint deep migration pathways on a
conventional seismic line – but chimney cubes can highlight subtle
features like vertical gas migration in the geopressured sections of the
Gulf of Mexico. This helps substantiate predictions of geochemists and
geologists that vertical migration is an important process in charging
Tertiary reservoirs in the Gulf of Mexico and in other similar basins
around the world. Chimney and
Distinguishing
Charged
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