East Taft Field, San Patricio County, Texas, Subtle Stratigraphic Trap: Implications for Exploration in a Supermature Province

R. R. Railsback

The shallow upper Frio producing trend along the downthrown side of the Vicksburg flexure in the lower Texas Gulf Coast is one of the world's supermature provinces for oil and gas exploration. Current emphasis in exploration must be for the subtle trap, the discovery of which has been precluded during the many years of intensive exploration. East Taft field is an excellent example of one such subtle trap. A stratigraphic oil accumulation in a barrier-bar washover sand, East Taft field had produced 2.35 million bbl of oil from 33 wells completed in an average of only 2.5 ft (0.76 m) of net oil sand. Traps of this type are numerous all along the trend, owing to the nature of the barrier-bar and adjacent lagoonal environments. These traps remain largely undiscovered, as they are never specifically explored for, and are commonly passed over as noncommercial when penetrated by wells. The economic potential of these subtle traps is enormous. Exploration programs geared specifically toward finding these reserves can be expected to provide an excellent return on investment. However, creative geological thinking and innovative engineering practices are requisite to the discovery and profitable development of these fields. For the explorationist who is willing to do the detailed structural and stratigraphic analysis required to identify these prospects, who understands the risks involved in exploration for these traps, and who is willing to innovate, these subtle stratigraphic traps truly represent a new frontier in an old producing province.

AAPG Search and Discovery Article #91042©1987 GCAGS and GC-SEPM Section Meeting, San Antonio, Texas, October 28-31, 1987.