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Abstract: Porosity Distribution in the Stuart City Trend, Lower Cretaceous, South Texas
D.G. Bebout, (1) R.A. Schatzinger, (1) R.G. Loucks (1)
The Lower Cretaceous Stuart City Trend is a complex of biogenic reefs, banks, tidal bars, channel fills, and islands that accumulated on a broad carbonate shelf encircling the Gulf of Mexico. A variety of carbonate facies were deposited in environments with a wide range of energy levels along this shelf-margin complex. Only 4 of these facies, however, have greater than 5 percent porosity and 5 millidarcys permeability -- the algae-encrusted miliolid-coral-caprinid packstone, mollusc grainstone, rudist grainstone, and coral-stromatoporoid boundstone. Rudist grainstone is potentially the most consistent in terms of porosity and permeability, thickness, and lateral extent.
Intraparticle, interparticle, and fracture porosity are present in the thick limestone section along the Stuart City shelf margin. Intraparticle porosity is common and in places reaches 20 percent although permeability in facies with intraparticle porosity is low. On the other hand, in facies with interparticle porosity of greater than 5 percent good permeability of up to 10 millidarys exists. Permeability in any facies may be enhanced by the presence of thin fractures which were noted to be common in several cores.
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ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES
(1) Publication authorized by Director, Bureau of Economic Geology, The University of Texas at Austin
Copyright © 1999 by The Gulf Coast Association of Geological Societies