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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 (^kgr) is linearly proportional to porosity (^phgr). 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(^kgr)-^phgr plots: from the high ^kgr, high ^phgr of synthetic sand packs and recently deposited sands, through poorly consolidated sands, through trends typical of consolidated sandstones, and into the low-^kgr, low-^phgr rocks typified as 'tight gas sands'.

Sandstones of different compositions follow different paths on a log(^kgr)-^phgr 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(^kgr)-^phgr trends vary from formation to formation.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana