Sequence Stratigraphy and Exploration Concepts of the Vicksburg Group

Abstract

Sequence stratigraphic analyses of the Gulf Coast Oligocene Vicksburg Group reveal that there was a coast-wide seaward shift of paralic facies at its lower boundary. The regional extent of the drop in relative sea level indicates that eustasy was the cause of the drop. A middle Vicksburg transgressive episode is also seen across the study area, though in some depocenters it is masked by the effects of sediment influx. The upper boundary of the Vicksburg is identified regionally by a change in depositional modes from progradational in the upper Vicksburg section to aggradational in the overlying lower Frio. Generally, the Vicksburg section corresponds to an Exxon sequence model with a Type 1 lower boundary (Jackson-Vicksburg), a lower Vicksburg lowstand system tract, a middle Vicksburg transgressive systems tract, and an upper Vicksburg highstand systems tract. Differences of some sequences analysis curves from this model occur on analyses from known depocenters, indicating that sediment influx variations may cause noncorrelation of sequence curves. The majority of petroleum fields with cumulative Vicksburg production of more than 1 bcf of gas and/or 1 MMBO produce from deltaic sandstones. Productive lowstand deltaic reservoirs were deposited in a shelf-edge to upper slope environment seaward of the firstmore » Vicksburg growth fault; deposits of shelfal deltas are the usual highstand reservoirs. Outer shelf depression fill deposits of highstand deltas front or prodelta origin account for most of the other reservoirs. The lowermost Vicksburg section of the lowstand systems tract in the Rio Grande embayment contain reservoirs of mass-flow or turbidite deposits. Potential exploration targets for the Vicksburg section still exist within all of these depositional settings.« less