ABSTRACT

Fabric and porosity changes resulting from compaction were studied in sandstones from three cores sampled at depths between 15,900 and 22,500 feet. Point counts of 30 thin sections indicate that 0.4% of the rock volume was lost by ductile grain deformation and 3% by pressure solution at both grain contacts and at widely spaced stylolites. Pre-cement porosities of eolian sandstone range from 27 to 35% (mean=29%), indicating that a total of from l0 to 18% porosity (mean=16%)was lost by compaction (assuming 45% initial porosity). The difference between the total porosity loss and the sum of the other two processes is assumed to be the porosity lost by grain rearrangement (mean=12.6%). The amount of pressure solution at grain contacts for each well is independent of depth, temperature, and amount of both quartz cement and total cement. Stylolites transect both grains and cements, which indicates they formed late in the diagenetic sequence.

Silica released by pressure solution at quartz grain contacts could not be the sole source and was probably not even the major source of quartz cement in the formation, because cementation by quartz preceeded the episode of strong pressure solution. In addition, the volume of silica released by pressure solution appears to be inadequate to provide the volume of quartz cement present.