Title: Aase and others, 1996
Author: Joyce Kibler
Company: USGS

Aase and others, 1996									Data Set 1
Reference:  Aase, N.E. P.A. Bjorkum, and P.H Nadeau, 1996, The effect of grain-coating microquartz on preservation of reservoir porosity: American Association of Petroleum Geologists Bulletin, v. 80, n. 10, p. 1654-1673.
Author's affiliation:  Statoil
Age:  Late Jurassic
Formation:  Ula Sandstone and Gyda Sandstone
Location:   Ula and Gyda Fields, Central Graben, Norwegian Sector, North Sea
Well:  15 wells
Depth range: 3300 - 4250 m
Depositional Environment:  offshore marine shelf
Grain Size:  See values in table.  Samples were selected to obtain a limited range in grain size.
Background:  This study was carried out to find why porosity values in these sandstones were greater than in other Jurassic formations at comparable depths of burial.  
Grain mineralogy:  Based upon xray diffraction analysis of 25 samples from 2 wells (table 2), and excluding 3 calcareous samples, quartz ranges from 62.3 to 79.5%, K-feldspar ranges from 6.8 to 15.2%, and plagioclase ranges from 6.4 to 12.1%.
Alteration:  The scanning electron microscope was used to estimate the amount of microquartz, macroquartz, clay, and carbonate cement (see table), with xray diffraction analysis on some samples as control. … “We designated sandstone samples as having a moderate (medium) amount of microquartz when there was a thin and continuous rim of microquartz around all the quartz grains and no or little pore-filling aggregates.  The amounts of clay (including diagenetic illite) and carbonate has been estimated in the same way.”
Conclusion:  The authors concluded that the presence of microcrystalline quartz on grain surfaces impedes the deposition of quartz cement.  They find that microquartz contents of 2 to 5% are optimal to preserve high porosity and permeability.
Comment:  The horizontal needles on the permeability-porosity plot are proportional to the sum of the clay and carbonate content in a sample.  Note that these values are classification ranks, not percentages.
Production:  oil
Core measurement conditions:  not given.
Data entry:  manual entry from table 1 of reference