Grigsby and others, 1992								Data Set 28
Reference:  Grigsby, J.D., J.M. Vidal, D.L. Luffel, J. Hawkins, and J.M. Mendenhall, 1992, Effects of fibrous illite on permeability measurements from preserved cores obtained in Lower Wilcox Group gas sandstones, Lake Creek field, Montgomery County, Texas: Gulf Coast Association of Geological Societies, v. 42, p. 161-172.
Authors' affiliation:  Bureau of Economic Geology at University of Texas at Austin; ResTech Houston
Age:  Paleocene to early Eocene
Formation:  G sandstone of Wilcox Group
Location:  Lake Creek Field, Houston Embayment, Montgomery County, Texas
Well:  LCU No. 48 well
Depth range:  11,526-11,605 feet
Depositional Environment:  “The G sandstone, composed of individual multistoried, stratigraphically heterogeneous reservoirs, is one of several 150- to 500-ft-thick upward-coarsening intervals that form part of the fluvial-dominated Brazos delta of the lower Wilcox Rockdale delta system. ... At the LCU No. 48 well, the G sandstone is 290 ft thick and consists of repetitive upward-thickening sandstones separated by mudstone-rich intervals.  .. Each parasequence corresponds to a period of deltaic progradation.”
Primary mineralogy:  “G sandstones are poorly to moderately well sorted, fine-grained, quartz-rich arkoses to lithic arkoses having an average composition of Q62F26L12.  … Detrital quartz averages 42.5% of the rock volume and ranges from 31.5% to 52.5%. ...”
Alteration:  The major authigenic minerals affecting reservoir quality are quartz overgrowths and fibrous illite.  Although quartz overgrowths have resulted in a permanent reduction in intergranular porosity in G sandstone reservoirs, this study found that fibrous illite, extending into and bridging pore throats, plays a major role in reducing permeability.
Production:  gas condensate.
Core measurement conditions:  Measured at net overburden pressure.  Permeability corrected for Klinkenberg effect.
Data entry:  manual entry from Tables 2, 3, and 4 from the referenced paper.