--> Facies and Stratigraphic Interpretation of the Upper Cretaceous Woodbine-Eagle Ford Interval in Leon, Madison, Grimes and Brazos Counties, Texas.

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Facies and Stratigraphic Interpretation of the Upper Cretaceous Woodbine-Eagle Ford Interval in Leon, Madison, Grimes and Brazos Counties, Texas.

Abstract

Abstract

The Upper Cretaceous interval in Texas is a proven prolific hydrocarbon system. The Eaglebine play in Central Texas is an emerging play with promising results to the operators. However, stratigraphic architecture of the Eaglebine play is poorly understood when compared to that of the Maverick Basin and East Texas Basin. The objective of this research is to narrow the stratigraphic uncertainties of the Eagle Ford-Woodbine Groups correlation between the East Texas and Maverick Basins and to predict the distribution of sand bodies in the active ‘Eaglebine’ interval in the Leon, Madison, Grimes and Brazos counties by integrating information from available wireline-logs and cores. In this study I propose a new stratigraphic architecture of this region and also estimate the preliminary petrophysical properties for the potential hydrocarbon bearing intervals in the study area.

The Buda Limestone-Austin Chalk succession thins as we move eastward toward the San Marcos Arch. This is due to the up lift and erosion at Base Austin Chalk (BAC) Unconformity. Wireline log interpretation suggests that the Woodbine Group sediments, which are dominantly siliciclastic, are a little over 500 feet thick in the updip Leon County significantly thins to 50 feet thick in the downdip Brazos County. This sudden shift is accounted for the Woodbine shelf break in the Leon-Madison Counties. The unconformably overlying Lower Eagle Ford Formation is relatively thick in Brazos and Grimes Counties. The lower part of the Lower Eagle Ford Group is carbonate rich shale with high GR and deep resistivity. This unit has potential of being a prolific play in the Brazos and Madison counties. The Upper Eagle Ford Group in this region is a mixture of siliciclastic and carbonate sediments. The proportion of carbonate sediments gradually increases upwards till the Base Austin Chalk Unconformity. The sandstones of Upper Eagle Ford Group have a good hydrocarbon reservoir potential.

This study lays a foundation for the stratigraphic architecture of the Upper Cretaceous interval in the study area and can be extremely helpful in understanding the regional stratigraphy from the East Texas Basin to the Maverick Basin when integrated with the seismic data for future research.