Exploration geologists and geophysicists have much in common in terms of tools and vocabulary when it comes to searching for hydrocarbons, but there are clear differences in approach. Certain occurrences of hydrocarbons are subtle in terms of their geologic setting. Others may be obvious in terms of geology, but subtle in their seismic expression. Little has been written about such traps other than what has appeared in works on stratigraphic applications for seismic data. It is also important to distinguish between subtle seismic expressions of traps and complicated seismic expressions. The complicated seismic expression, while difficult to interpret, is not often overlooked. Noting subtle seismic signature in the first instance

End_Page 912------------------------------

is another matter. A challenge is presented when both geology and seismic expression entail subtlety. These problems are encountered frequently and often are treated with great success. Detection of fracture porosity in carbonate rocks is an example.

Bounds and nature of seismic visibility and detectability are developed for families of lithologies of exploration interest. Geometric considerations are examined in the context of subsurface definition. Tools and techniques currently available for treating seismic data for the subtle trap are described, and uses for these tools and methods are given. In reconciling geologic and geophysical views toward the subtle trap, a more complete definition of the concept and a still larger family of exploration targets are provided.

End_of_Article - Last_Page 913------------