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Variation in Reservoir Quality and Porosity-Permeability Trends in Paleogene Wilcox Sandstones, Texas and Louisiana Gulf of Mexico Coast

Dutton, Shirley P.*1; Loucks, Robert 1
(1) Bureau of Economic Geology, The University of Texas, Austin, TX.

Petrographic and petrophysical analysis of Wilcox sandstones from the Texas and Louisiana Gulf coast was conducted to document evolution of reservoir quality during burial diagenesis. Wilcox samples were deposited in the Holly Springs delta of Louisiana, the Houston delta of the upper Texas coast, and the Rosita delta of the lower Texas coast. Petrographic analysis of 534 Wilcox thin sections was combined with core-analysis data from >10,000 core samples to determine regional variation in the evolution of pore types and porosity-permeability trends with increasing burial depth and temperature. The results provide insight into reservoir quality of deeply buried Wilcox sandstones beneath the Gulf of Mexico shelf and in the deep Gulf.

Petrographic data show that pores in Wilcox sandstones change from a mix of primary and secondary pores and micropores at lower temperatures to predominantly secondary pores and micropores at temperatures >125°C. Primary porosity, which has the greatest effect on permeability, decreases by compaction and cementation at similar rates in all three Wilcox study areas. Average primary porosity decreases from an estimated 40% at the time of deposition to 5-8% by 125°C and 1-2% at temperatures >200°C.

The larger core-analysis data set was used to calculate porosity-permeability transforms within different temperature slices in each study area. At temperatures <100°C, the transforms for all three areas are similar. At 100°-150°C, Wilcox sandstones in Louisiana have the highest permeability per porosity unit, and those in upper Texas have the lowest. At temperatures >200°C, sandstones from lower Texas have higher permeability per porosity unit than those from upper Texas; no Louisiana Wilcox samples were available. These data suggest that high-temperature Wilcox sandstones beneath the present shelf and in the deep Gulf that were sourced by the Holly Springs and Rosita deltas may have better reservoir quality than do sandstones derived from the Houston delta.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California