Print this pageGrain Size, Diagenesis and Permeability Prediction in Reservoir Sands
PRINCE, C. M., R. EHRLICH, and C. J. MURRAY
Modern procedures in basin history 
analysis
can predict approximate grain
size as a function of depositional environment and basin location. The
relationship between grain size and permeability is approximately known for
unconsolidated sediments. This relationship is modulated by diagenesis in
lithified sandstones. In unlithified sands, log permeability is proportional to
log grain size with a constant of proportionality ranging from 1.2 to 1.7.
Diagenesis may change this coefficient or render the relationship more diffuse-
such changes may be a way to quantify the degree of diagenesis in a sandstone.
Such quantification requires a way to measure grain size from thin section that
is insensitive to the biases due to the effect of sectioning and to the
existence of quartz overgrowths. Fourier analysis of binary images of thin
sections can provide this information because the distances between pore centers
are the same as between grain centers and remnants of intergranular porosity
tend to remain even after considerable diagenesis. Results from analysis
of the
Perry Sandstone (Carboniferous) illustrate the procedure. The plot of grain size
vs. permeability displays two relationships; 1) for sandstones with homogeneous
texture the constant of proportionality is approximately five; 2) for samples
containing patchy carbonate cement the constant is approximately seven, a value
so great as to be of little practical value.