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By MARLAN DOWNEY

Discriminating Character

Perhaps a review -- and awareness -- of the past may make us better geologists in the future.

"Genesis of Oligocene Sandstone Reservoir, Seligson Field, Texas," by Robert H. Nanz, was printed in the AAPG BULLETIN, Volume 38, January 1954.

In 1954, Bob Nanz published an outstanding paper that documented the environment of deposition of a particular Oligocene sandstone, using subsurface data.

Analysis of the well log and core information indicated that the linear Oligocene reservoir:

• Was deposited on an alluvial flood plain.
• Had a trend at right angles to the Oligocene marine depositional strike.
• Was very similar to modern sands within the Texas Rio Grande.

Nanz demonstrated that lenticular alluvial sands could be differentiated from dimensionally similar long, narrow beach sands.

His paper was one of the first to make use of such discriminators as the character of included mud fragments, the vertical variations in grain size, the sorting of the sand grains and the character of the associated shales.

This study provided powerful geologic tools for identifying sandstone depositional environments and in making directional predictions of sandstone reservoirs.

Nanz went on to be vice president of Shell's Bellaire Research Laboratory, and it is no coincidence that the laboratory produced such Sidney Powers medalists as Rufus LeBlanc, Bob Sneider, Bert Bally and James Lee Wilson.

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