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William A. Ambrose
"The Shelf-to-Slope Transition in the Upper Cretaceous Woodbine Group in Northern Tyler and Southeastern Polk Counties, Texas:
Facies Variability and Controls on Reservoir Quality"

11:30 AM Wednesday, December 16, 2015
at the Cascades
4511 Briarwood Road
Tyler, TX 75709


William A. Ambrose is a Research Scientist at the Bureau of Economic Geology. He received a Master of Arts degree in geological sciences in 1983 from the University of Texas at Austin. Since joining the Bureau of Economic Geology in 1987, he has worked on a variety of projects at the Bureau, including characterization of the Woodbine Group in the East Texas Basin, Frio fluvial and deltaic reservoirs in South Texas, tight-gas reservoirs in the Cleveland Formation in the Texas Panhandle, co-production of gas and hot brine from Oligocene reservoirs in the Texas Gulf Coast, evaluation of coalbed methane reservoirs in Rocky Mountain basins, and reservoir characterization and basin analysis studies in Venezuela and Mexico. He is currently the principal investigator of the Bureau’s STARR (State of Texas Advanced Oil and Gas Resource Recovery) program, past president of the Energy Minerals Division (EMD) of AAPG, chair of the EMD Coal Committee, and past co-chair of the AAPG Astrogeology Committee. His contact information is: email:, telephone: 512-471-0258, address: Bureau of Economic Geology, The University of Texas at Austin, University Station, Box X, Austin, TX, 78713-8924.



"The Shelf-to-Slope Transition in the Upper Cretaceous Woodbine Group in Northern Tyler and Southeastern Polk Counties, Texas: Facies Variability and Controls on Reservoir Quality"
by William A. Ambrose, Tucker F. Hentz, and David Smith
Bureau of Economic Geology
The University of Texas at Austin

The Cenomanian Woodbine Group in northern Tyler and southeastern Polk Counties in Texas composes a shelf-to-slope transition along the upper Cretaceous shelf margin. The productive Woodbine section in northern Tyler County consists of a shallow-marine deltaic succession composed of delta-front, distributary-channel, transgressive, and highstand-shelf facies. This shallow-marine interpretation is based on (1) Skolithos and Cruziana ichnofaunal assemblages, (2) upward-shoaling, high net-to-gross and sandy successions with an upward progression from lower-flow-regime ripples to upper-flow-regime planar stratification, and (3) the proximal paleogeographic position of the Woodbine succession along the Edwards Reef Trend.

Muddy Woodbine slope deposits, downdip of the Cenomanian shelf edge in northwestern Tyler County, typically contain thin (commonly <1-ft [<0.3-m]) beds of very fine grained levee sandstones interbedded with sparsely burrowed mudstone. Sandy slope facies, consisting of channelized-levee deposits, are composed of multiple upward-fining sandstone beds defined by incomplete Bouma sequences containing graded beds and thin (<2-in [5.1-cm]) zones of convolute bedding. Other sandy slope deposits are represented by heterolithic, erosion-based debris-flow facies with zones of chaotic bedding.

Permeability and porosity data indicate that facies with greatest reservoir quality in Woodbine shallow-marine systems occur in distributary-channel and proximal-delta-front facies, although original porosity has been modified by diagenesis. In contrast, Woodbine slope facies in western Tyler County have low reservoir quality, with locally productive channelized-levee facies. Although there is a decrease in porosity and permeability with depth, variation in reservoir quality exists between and within both shallow-marine and deepwater facies, a function of grain size and stratification.