Facies and Stratigraphic Interpretation of the Upper Cretaceous Woodbine-Eagle Ford Interval in Leon, Madison, Grimes and Brazos Counties, Texas
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The Upper Cretaceous in Texas is a proven prolific hydrocarbon system. The “Eaglebine” in Central Texas, which includes both the Eagle Ford and Woodbine intervals, is an emerging play with promising results. However, stratigraphic architecture in this region 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 Woodbine-Eagle Ford correlation between the East Texas and Maverick Basins and to predict the distribution of sand bodies in the active “Eaglebine” interval in Leon, Madison, Grimes and Brazos Counties by integrating information from available wireline logs and cores. A new stratigraphic interpretation of this region is proposed, and estimates of the petrophysical properties for the potential hydrocarbon-bearing intervals in the study area are presented. The Buda Limestone-Austin Chalk succession in this study area, which brackets the “Eaglebine”, thins westward due to uplift associated with the San Marcos Arch and erosion at the Base Austin Chalk (BAC) Unconformity. Wireline log interpretation suggests that Woodbine Group sediments, which are dominantly siliciclastic, are a little over 500 feet (152.5) thick updip in Leon County and thin dramatically to fifty feet (15.25 m) thick downdip in Brazos County. This transition records the Woodbine shelf break in Leon-Madison County area. The unconformably overlying Lower Eagle Ford Formation is relatively thick in Brazos and Grimes Counties. The lower part of the Lower Eagle Ford Formation is carbonate-rich shale with high gamma ray and formation resistivity. This unit has the potential to be a prolific play in Brazos and Madison Counties. The Upper Eagle Ford Formation in this region is a mixture of siliciclastic and carbonate sediments. The proportion of carbonate sediments gradually increases upwards to the Base Austin Chalk Unconformity. The sandstones of Upper Eagle Ford Formation have good hydrocarbon reservoir potential based on their non-shale porosity values and high sand percentage. This study resolves the stratigraphic architecture of the Upper Cretaceous Woodbine-Eagle Ford interval in the study area and will be helpful in understanding the regional stratigraphy from the East Texas Basin to the Maverick Basin when integrated with seismic data.
Vallabhaneni, Sridharan (2016). Facies and Stratigraphic Interpretation of the Upper Cretaceous Woodbine-Eagle Ford Interval in Leon, Madison, Grimes and Brazos Counties, Texas. Master's thesis, Texas A & M University. Available electronically from