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Exploration Geophysics
Craig Beasley

The dominant feature on the landscape for exploration geophysics remains the tough economic climate that our industry is experiencing. However, despite oil prices recently topping $40.00 per barrel, commodity pricing for metals and minerals hitting similar highs, and increasing concerns about the environmental impact to the near-surface, commercial activity in applied geophysics remains steady, and technology advancements continue at a rapid pace.

Perhaps the most exciting current arena is that of deepwater basins around the world. An emerging theme in deepwater exploration is the need to provide near-constant (or on-demand) seismic reservoir imaging. This need, in turn, is driving algorithmic and computer science research and development to enable the processing and delivery of data in near real-time.

A second aspect of the deepwater play involves the need to image around, beneath and through salt bodies, which requires depth migration. Commercial applications of depth migration began to grow rapidly in the 1990s and have continued to evolve apace.

Another significant trend in the marine environment is the move towards high-fidelity data both in terms of the acquisition equipment itself and in survey design and data processing. Repeat seismic techniques (4-D seismic) not only are important in the context of the critical deepwater basins, but also are key in many production environments. The low strength of the 4-D signal (defined as the difference between multiple towed conventional 3-D surveys) requires high-fidelity data.

Moreover, complex geology and subtle seismic expression of facies are better imaged by high-fidelity data. The need for resolution has driven the development of more accurate navigation and positioning hardware and software. Moreover, there is a demonstrated need in 4-D seismic to be able to accurately repeat the positioning of sources and receivers in each repeated survey. To this end, applied geophysicists have developed so-called steerable seismic streamers that can impart as much as a 3-degree correction to the normal, or unaided, path of the streamer. Achieving this technology, long considered the holy grail of marine seismic research, is a great step for the community.

Resolution is an issue in land seismic data as well. One of the challenges with high-resolution land data is to take advantage of the benefits of arrays to cancel high-amplitude noise such as ground roll, while at the same time retaining the benefits of dense sampling. Development of numerical algorithms that handle single sensor data in this manner is proving useful in this regard. These technologies are coming into use to better image the all-important reservoirs of the Middle East and will likely soon spread to other provinces.

These examples are only a sampling of the exciting developments occurring in traditional surface seismic exploration and development applications. There are also new applications in other areas. For example, surface electromagnetic surveys are being used for direct hydrocarbon detection.

Using both the magneto-telluric method as well as a controlled electromagnetic source, companies are reporting successes in deepwater marine environments in combining electromagnetic data with other subsurface information to reduce risk in exploration drilling. And electromagnetic surveys are breaking ground in difficult mountainous terrain where surface seismic is problematic at best. On the horizon, researchers are conducting work to extend near-surface and potential field methods for use in exploring Mars.

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Beasley is chief geoscientist for WesternGeco and Schlumberger Fellow and 2003-2004 president-elect of the Society of Exploration Geophysicists.

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