ABSTRACT

The South Texas Frio Trend extends along the coast from the Rio Grande River on the south through Calhoun and Victoria Counties on the north. The discovery of oil in Refugio Field of Refugio County in 1928 led to the development of the "Golden Trend."

The sediments of the Frio formation were deposited on a sinking continental shelf by transgressive and regressive seas, over an eroded Vicksburg surface. The Anahuac marine wedge overlaps the downdip Frio. The Catahoula sands and shales overlie and are in contact with the Anahuac wedge downdip and the Frio formation updip.

Numerous facies changes and down-to-the-coast fault systems have accounted for the majority of the large producing fields. Approximately ninety percent of the Frio and Anahuac Fields that have produced over 25 million barrels of oil are located along the Vicksburg Flexure,(FOOTNOTE 2) Fields with an accumulative total of less than 25 million barrels of oil make up a large share of the tremendous reserves of this so-called "Golden Trend." Producing structures include accumulations along the downthrown segment of down-to-the-coast faults, up-to-the-coast fault closures, closures on the up-thrown side of down-to-the-coast faults and salt-generated structures.