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3-D Seismic Sweeps Through Time*
By
R. Randy Ray1
Search and Discovery Article #40115 (2004)
*Adapted for online presentation from the Geophysical Corner column in AAPG Explorer, February 2003, entitled “3-D Seismic Maps Tell Tales,” and prepared by the author. Appreciation is expressed to him and to Larry Nation, AAPG Communications Director, for their support of this online version.
1R-3 Exploration Corp, Lakewood, CO 80228-4358 ([email protected])
Introduction
Three-dimensional seismic has become the tool of preference for petroleum exploration and development. Over the last 20 years, advancing technology in seismic recording systems has allowed the acquisition of large areas of 3-D seismic data, and high drilling success rates have fueled the use of 3-D seismic in basins around the world, in both onshore and offshore arenas.
As 3-D seismic has swept across the U.S. onshore, it leaves evidence of past activities where explorers saw potential in various basins. Early surveys were targeted for evaluating infill drilling around existing fields. Over time, surveys spread along productive trends looking for new fields. The current pattern of 3-D seismic coverage is a good indicator of exploration maturity.
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Patterns of ExplorationLocation information about where 3-D seismic surveys have been shot is available from various sources. The maps shown here were compiled from public records in counties where survey locations must be reported as part of the acquisition procedure and from the many companies who place their proprietary surveys with seismic brokers for sale or trade. Although these maps may not contain all of the surveys shot, they do represent the general density of coverage in various areas -- and they reveal an interesting and thought-provoking view of seismic activity and thus exploration activity since the early 1980s, when 3-D seismic became widely available. Looking at 3-D seismic coverage maps in Texas and Oklahoma (Figure 1) and over the Rocky Mountain basins (Figure 2), one sees a pattern of decreasing seismic coverage as you move from offshore to onshore areas. Although one might think this pattern shows the overall cost increase of acquisition, it primarily reflects the economic success of 3-D seismic in finding hydrocarbon entrapments. The exploration of Gulf of Mexico offshore areas is mostly dependent on seismic (no outcrops to map!), so the coverage is usually 100 percent of the area. In fact, many offshore areas have more than 100 percent coverage since there may be multiple surveys acquired by different companies over the same area. Moving onshore in Texas, the coverage stays high at 60 to 70 percent. Early surveys were acquired over fields and then spread along coastline parallel faults looking for new traps.
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