ABSTRACT

The Late Oligocene Vicksburg Formation of the Texas Gulf Coastal Plain lies within the Tertiary depositional wedge between the Upper Eocene Jackson Group and the Upper Oligocene Frio-Catahoula Formations. Across the state of Texas there are at least 373 fields producing from the Vicksburg Formation; as of January 1, 1982, these fields had produced cumulative totals of over 73 million barrels of oil and 274 billion cubic feet of gas. In the Rio Grande embayment of South Texas, the Vicksburg Formation has long been recognized as a prolific petroleum producer from shelf-edge delta sand reservoirs. In the Houston embayment of the eastern Texas coastal plain the Vicksburg producing sands were deposited in a deltaic systems tract positioned on the relict Jackson shelf platform. Regional depositional systems analysis of the Vicksburg Formation of the San Marcos arch has demonstrated that this unit is dominated by a belt composed of a strike-oriented paralic sand complex. The depositional environments responsible for these interrelated coastal sands include delta flanks and their associated shorezone, strand plain and barrier systems. These paralic sands are the lateral equivalent of the Vicksburg deltaic system in the Houston embayment and of the extensively growth faulted deltas within the Rio Grande embayment. Across the Texas coast the fields producing from the Vicksburg are associated with the Vicksburg growth fault zone. The producing reservoirs are most commonly found in the uppermost sands of the deltaic sections. Most of the fields have anticlinal and fault closures or structural-stratigraphic combination trapping situations.