Print this pagePetrographic Reservoir
Characterization—Direct Measurement and Analysis of 
Pore
and Grain Size Data
from Thin Sections
Thin section petrography has traditionally offered only
limited insights into the details of sedimentology
and even less into reservoir characterization. Petrographic
reservoir characterization, making comparisons to engineering and petrophysical data, has not been feasible. Utilization of
CCD camera control software provides the means to gather grain and porosity
data that can be directly compared to conventional core analysis and mercury
injection capillary pressure (MICP) data. Samples of Dakota “J,” Nugget, and Mesaverde sandstones were analyzed and compared. Control
samples were used to estimate the effects on grain size measurements in thin
section. Data gathered consist of length and width measurements of large
numbers of sand grains. Frequency distributions of these data provide a
sensitive means of discriminating between samples. Interactive selection of
pores impregnated by blue-stained epoxy allows gathering measurements of pore
area, perimeter, and equivalent circular diameter (ECD). Frequency distributions
of pore area and total pore area show the relative contributions to porosity of
pores of different sizes. Plotting frequency distributions of pore ECD with
grain size shows the relative contribution of intergranular
and moldic porosity. Plotting ECD with the pore area
and total pore area frequency distributions reveals the contribution of each
pore size class to total porosity. Image analysis shows that the interactive
pore selection process captures over 90% of the blue-impregnated porosity, down
to a few microns. Using this calculation, the pore area data can be plotted by
size
class, simulating an MICP curve.