Diagenetic and Depositional Controls on Reservoir Properties in the Eolian Pennsylvanian-Permian Tensleep Sandstone, Sussex Field, Wyoming

Michael D. Wilson¹ and Warren J. Winters^2
1 Geological Consultant, Lakewood, CO
² Anadarko Petroleum Corporation, The Woodlands, TX

The Tensleep Sandstone in the Sussex Field, Johnson County, Wyoming consists primarily of fine-grained, well sorted, highly quartzose eolian sandstones. Very thin (a few micrometers or less) illitic inherited clay rims extensively coat framework grains and severely limit quartz overgrowth cementation in most samples. These rims are present at most grain contacts and, as a result, promote suturing by pressure solution or clay-aided dissolution.

Compaction loss produced by suturing is the dominant mechanism of porosity reduction (average of 57% of total porosity loss). Compaction loss exhibits a strong negative correlation with pore-filling cements but is still significant (5 to 10% porosity loss) at cement abundances of 20 to 25%. Both early finely crystalline dolomite and later coarser quartz overgrowths display an equivalent ability to inhibit compaction loss. This indicates that the early introduction of cements in such sandstones, even in large amounts, does not offer enhanced porosity preservation relative to that provided by later stage cements.

Measured porosities tend to be highest (20-25%) in sandstones which have experienced extensive compaction loss but contain little or no cement, and lowest (5-10%) in those with abundant cement. Permeabilities are controlled primarily by porosity (cement abundance), grain size and sorting. A few samples in which clay rims and matrix clays are relatively abundant (3 to 5%) commonly display very severe suturing and have very low porosities. Thin (0.01 to 0.5mm) dense granulation zones, presumably generated during Laramide deformation, are present in scattered samples and may serve as local baffles to fluid flow.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005