Computerized Quantitative Petrographic Image Analysis of Wilcox Sandstone, Louisiana Gulf Coast

James R. Garrison, Jr., Roland E. Gerard, Federica M. Manni

Computerized quantitative petrographic image analysis measures first-order parameters such as the abundance, cross-sectional area, length, width, diameter, and perimeter of a pore feature very rapidly and with great accuracy and precision. From these first-order parameters, second-order parameters such as shape factors, aspect ratios, specific surfaces, and pore size and roughness distributions can be calculated. These parameters can then be used to calculate even higher order parameters such as porosity, permeability, and capillary pressure curves.

Analyses were performed on 350 samples from nine wells from the Wilcox Formation in southern Louisiana to characterize the two-dimensional rock pore complex of this Gulf Coast reservoir rock. Empirical equations were derived that describe relationships between first- and second-order image analysis parameters and conventional laboratory porosity and permeability measurements from core plugs. Because image analysis represents only a two-dimensional section of the pore complex, these equations provide only an "index" of porosity and permeability which is restricted by the limited relationship of the two-dimensional section to the three-dimensional core plug. Both indices were derived from simplified equations, using parameters such as pore cross-sectional area, pore shape, and pore size The permeability and porosity indices were correlated to the conventional laboratory permeability and porosity data (r = 0.855 and r = 0.804, respectively). First- and second-order image analysis parameters were also used to calculate mercury injection capillary pressure curves. Such curves were calculated from image analysis data from nine Wilcox samples and were scaled based on their correlation with actual measured brine capillary pressure curves.

Porosity and permeability indices, shape factors, and pore smoothness and roughness spectra were used as a quantitative indicators of reservoir quality for the Wilcox sandstones. The parameters used to derive these image analysis features were used to perform Fuzzy c-means cluster analysis. The cluster analysis was then used to quantify membership in reservoir quality subclasses.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.