Porosity Distribution in the Stuart City Trend, Lower Cretaceous, South Texas

Abstract

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 four of these facies, however, have greater than 5 percent porosity and 5 millidarcys permeability-the algae-encrusted miliolid-coral-caprinid packstone, mollusk 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, in places reaching 20 percent, is common although permeability ability in facies with intraparticle porosity is low. Facies with interparticle porosity of greater than 5 percent have good permeability of up to 10 millidarcys. Permeability in any facies may be enhanced by the presence of thin fractures which were noted to be common in several cores. FROM TRANS. GCAGS, V. 27, P. 177-199. End_of_Record - Last_Page 3---------