Abstract: Spatial Variation in Porosity--New Concept

F. W. Preston, C. D. Conley, G. Watson

Image-analysis processors have been used in a variety of petrographic studies for rapid and precise measurement of petrographic parameters. Recent modifications in equipment allow measurement of the spatial variation in porosity over the area of standard petrographic thin sections.

Formation porosity conventionally has been estimated from well logs and by core analysis. No devices have been available to measure variation in porosity at the microscopic level, although the importance of such variation long has been recognized. The image-analysis equipment described allows measurement of porosity at any scale attainable through conventional petrographic microscopes.

Sandstone reservoir rocks first are impregnated with red-dyed epoxy resin to provide optical contrast. Video processing discriminates constituents on the basis of differing light transmission or gray level. Thus, pore space is discriminated uniquely from clear or opaque grains. Total area of discriminated constituents is computed directly by the scanner. Variation in porosity across a thin section can be measured by traversing the thin section and measuring porosity within a succession of small areas. Size of the scanned area can be controlled by optical magnification of the microscope and by electronic adjustment of the monitor-screen size. Subareas of a scanned area are sampled by means of a rectangular electronic "window," whose size, shape, and position can be controlled on the ma n image.

Examples from varied reservoir sandstone types illustrate the application of the technique.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA