Stratigraphic and Depositional Context of the Eaglebine Play: Upper Cretaceous Woodbine and Eagle Ford Groups, Southwestern East Texas Basin
The Woodbine and Eagle Ford Groups of the Eaglebine play of the southwestern East Texas Basin have generated considerable interest because of their potential for new hydrocarbon production from both sandstone and mudrock reservoirs. However, the play's stratigraphic and depositional relations are complex and directly relate to the play's exploration challenges.
Productive Woodbine and Eagle Ford (Sub-Clarksville) sandstones intertongue with a poorly defined, subregional mudrock-dominated interval that thins southwestward toward the San Marcos Arch. We propose dividing this succession into two intervals:
- Lower unit, a high-gamma-ray unit at the base of this mudrock succession that is inferred to be equivalent to the Maness Shale and to part of the lower Eagle Ford Group on the San Marcos Arch, and
- Upper unit, a basinward-thickening zone of consistently lower gamma-ray log facies inferred to be equivalent to the Woodbine Group, Pepper Shale, and Eagle Ford Group of the East Texas Basin. Because the Cenomanian-Turonian boundary occurs within the Eagle Ford Group of the East Texas Basin and the lower Eagle Ford section of the San Marcos Arch, most of the Maness-through-Eagle Ford succession exists as a much-thinned (<50 ft [15 m]) section on the arch.
Basinwide integration of the Woodbine sequence-stratigraphic framework shows that the number of fourth-order sequences in the unit decreases westward from 14 in the basin axis to no more than 9 in the most active part of the Eaglebine play because of their systematic depositional pinch out approaching the western basin margin. Depositional facies of the Woodbine sequences vary within the study area, even between stratigraphically adjacent intervals. On-shelf siliciclastic systems include highstand, fluvial- and wave-dominated delta deposits and lowstand, incised-valley-fill fluvial strata. The Eagle Ford Group consists of three fourth-order, highstand-dominated sequences capped by the Sub-Clarksville sandstones that accumulated after the major late Cenomanian-early Turonian flooding event recorded by a basinwide transgressive systems tract at the base of the unit.
AAPG Datapages/Search and Discovery Article #90214 © 2015 Southwest Section AAPG Annual Convention, Wichita Falls, Texas, April 11-14, 2015