--> ABSTRACT: Pore Types and Their Distribution in Wilcox Formation, Central Gulf Coast, by Kung-Chou Chuang and Earle F. McBride; #91036 (2010)

Datapages, Inc.Print this page

Pore Types and Their Distribution in Wilcox Formation, Central Gulf Coast

Kung-Chou Chuang, Earle F. McBride

Point counts were made of 141 samples (depths of 104 to 14,280 ft) from 13 cores in 6 counties to assess the abundance and distribution of various types of pores visible in thin sections impregnated with dyed epoxy. Porosity averages 13.7% and decreases at a rate of 0.6%/1,000 ft. However, the rate of decrease of maximum porosity values is twice the above rate. The average abundance of pore types as percent of total rock is 4.1% intergranular pores, 3.3% micropores in rock fragments, 2.2% intragranular pores in feldspar, 2.5% micropores in clay minerals, 1.2% oversize pores, 0.1% intragranular pores in igneous/volcanic rock fragments, and 0.4% intragranular pores of other types. If all intergranular pores and micropores within clays (mostly authigenic) are primary, then p imary pores make up an average of 46% of total porosity. Thus, secondary pores are more abundant than primary pores, even using a very conservative approach.

Intergranular pores and oversize pores are the only pore categories that have statistically significant depth trends: both decrease with depth. Intergranular pores have a positive correlation (r = +0.83) with oversize pores and kaolinite cement (r = +0.42). Both correlations are expected because complete dissolution of grains is most effective in sandstones with abundant intergranular pores, and the formation of kaolinite is favored in sandstones with large pores and high formation-water flux. The loss of K-feldspar at depths greater than 10,000 ft (3,048 m) is not manifested by a comparable volume of oversize pores.

Only a few pore types show regional trends, in part because of sparse control. However, the map of intergranular porosity shows an elongate northeast trend of high values that follows the trend of growth faults in the area. This pattern raises the question whether some intergranular pores may be secondary pores that formed by formation-water flow focused along growth faults.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.