Philip H. Nelson1,
Joyce E. Kibler1
(1) U. S. Geological Survey, Denver, CO
Abstract: Evolution of permeability-porosity trends in sandstones
In many sandstone reservoirs,
plots of core data show that the logarithm of permeability () is linearly proportional to porosity (
). Coherent trends are usually found if the
data are derived from individual formations. We have compiled and replotted
published permeability-porosity data, and extracted a trend line summarizing
each formation. The trend lines trace the evolution of permeability-porosity
trends on log(
)-
plots: from the high
, high
of synthetic sand packs and recently deposited sands, through poorly
consolidated sands, through trends typical of consolidated sandstones, and into
the low-
, low-
rocks typified as 'tight gas sands'.
Sandstones of different
compositions follow different paths on a log()-
plot. High-quartz sandstones with quartz
cement form the low-porosity bound for all sandstones, preserving good
permeabilities at low porosity (<10%). In these rocks, interconnected pore
throats are preserved at the expense of pore space between adjacent grain
faces. Such rocks are typified by porosity values ranging from 4 to 10% at 1
millidarcy and have the steepest slopes of all sandstones, that is, small
porosity changes are associated with large permeability changes. The trend
lines for sandstones with lower quartz content plot systematically at higher
porosities than the quartz arenites.
Within any given formation,
permeability is distributed over two to six orders of magnitude. Coarser grain
sizes result in the highest permeabilities and porosities, very fine grained
and silt sizes result in the lowest. Despite these tremendous ranges in
permeability, the data fields remain fairly coherent, although the slope,
intercept, and degree of scatter of these log()-
trends vary from formation to formation.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana