Abstract: Common Factors Among Atypical Fields

By

W. H. (Bill) Roberts III

Certain factors are functionally relevant to the occurrence of typical as well as atypical oil and gas fields. Consideration of such factors leads us to regard the distinction between typical and atypical fields as a matter of degree. For purposes of discussion, however, attention is focused on the more clearly atypical fields.

In a study of the workings of oil and gas fields, it is quite possible to reach the right conclusions for the wrong reasons. In other words, we may observe an apparent relationship between the presence of oil or gas and certain geological or geochemical factors without determining the true causality of that relationship (which could involve other vital factors unperceived). Thus, our conclusions can be founded on mere coincidence; and once reached, those conclusions may carry a lot of conceptual momentum.

At this stage in our knowledge of petroleum origin we probably stand to learn more from the "atypical" than from the "typical." Why? Because some of our tacit assumptions are challenged. The atypical situation forces us to answer new questions. The new answers then may enable us to fine-tune the search for more dependable oil and gas prospects-typical or otherwise.

Some pertinent criteria of effective entrapment which can be examined in both typical and atypical fields are: upward reservoir convergence, stratigraphic shunting, structural coherence, local cover weakness, near-vertical faulting, differential compaction, deep-water discharge, minimum potential energy, hydrothermal chimneys, and hydrochemical plumes.

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