--> Future Contributions of Small Field to U.S. Gas Discoveries, by R. Nehring; #90986 (1994).

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Abstract: Future Contributions of Small Field to U.S. Gas Discoveries

Richard Nehring

In most recent assessments of U.S. natural gas resources, small fields are expected to be major contributors to future discoveries. This expectation is based largely on a theoretical argument. To test whether this expectation is justified, we examined the number, geological characteristics, and discovery history of all small fields (both oil and gas) between 3 and 12 Bcfe discovered in the United States through 1992.

Although small fields are ubiquitous, they are highly concentrated in a few geological environments. For clastic reservoirs, fluvial plays provide the predominant small field environment. For carbonate reservoirs, pinnacle reef plays are the classic small field environment. Overall, small fields are most concentrated in areas characterized by low rates of sedimentation and low levels of tectonic activity. Where both sedimentation rates and tectonic activity is high, the field size distribution is markedly different.

Because small fields are predominantly shallow, they are also predominantly oil fields. Unless small fields are sourced by a Type III source or are adjacent to a deeper basin in which gas generation could occur from Type and Type II sources, their type environments are not conducive to gas generation. Moreover, because they are shallow, they are also concentrated in areas that are now highly mature in terms of exploratory drilling density.

Our knowledge of the characteristics of known small fields thus does not support the contention that very large amounts of natural gas remain to be discovered in small fields.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994