Upper Frio Formation Sequence Models: Southeastern Louisiana Subsurface

Abstract

The subsurface upper Frio Formation is characterized by interbedded carbonate and siliciclastic facies as represented by electric log and fragmented conventional core data. Resistive zones on electrical logs represent a range of composition from pure limestones to impure, iron-rich, dolomitic sandstones. These zones were tested for sequence stratigraphic utility as chronostratigraphic surfaces by using multiple seismic and electric log cross sections. Regional seismic data documents a late Oligocene age for the upper Frio Formation based on relationships with published coastal-onlap curve data. Electric log cross sections demonstrate that six sequences are present within the upper Frio Formation. Sequence boundaries, systems tracts, parasequence set stacking patterns, and marine flooding surfaces are not visualized by individual electric log patterns, but only with multiple electric log cross-section sets. Digitized electric log cross sections demonstrate basinward and landward shifts of facies, truncation of underlying highstand systems tracts or entire sequences, vertical stratal successions indicative of deepening water, and facies changes that suggest relative sea-level fluctuations. All oil production in the upper Frio Formation is entrapped in lowstand systems tract siliciclastics that are overlain by low-porosity, shelf edge-parallel carbonate banks. The carbonates are diagnostic of late lowstand to early highstand systems tract deposition. Shallow, biogenicmore » gas production is found landward of the shelf break in the highstand systems tract siliciclastics.« less