Abstract: Can Adobe Photoshop be Used to Quantify Sandstone Porosity?

MORSE, MELISSA J. and JAMES R. BOLES, Department of Geological Sciences, University of California, Santa Barbara, 93106-9630

The Photoshop petrographic image analysis method (PPIA) is used for rapid estimation of sandstone porosity from digitized images of blue epoxy impregnated petrographic thin sections. Porosity is measured by cutting blue pixels from the image using Adobe Photoshop and pasting them into a new image. The blue pixels are then measured using Photoshop's histogram function. Previous results indicate a need to calibrate this method to the conventional Helium gas expansion method due to the consistent underestimation of porosity values using PPIA.

An attempt has been made to calibrate these two methods of determining sandstone porosity through analysis of well characterized sandstone standards. We find that the presence of various clay phases causes a significant underestimation of porosity from PPIA. This finding supports the speculations of previous workers that much of the discrepancy between image analysis porosity values and Helium porosity values is due to microporosity, such as that caused by intergranular pores and cracks in fine grained clay. Additionally, some correlation is observed between increased pore boundary roughness, quantified by the ratio of pore area to pore perimeter, and the image analysis-Helium porosity discrepancy. This is attributed in part to an observed pixel-scale zone of fuzziness which is believed to represent the limit of resolution of the pore boundary. An equation was developed relating image analysis porosity to Helium porosity for samples with less than one darcy permeability. Some correlation is observed between porosity calculated from this equation and Helium porosity.

AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California