BERESKIN, S. ROBERT, GREGORY D. LORD, and LAWRENCE B. OWEN, TerraTek Inc., Salt Lake City, UT
ABSTRACT: Quantitative Porosity Measurements of Known Reservoirs Using Confocal Microscopy
When compared to traditional, transmitted light petrography, reflected ultraviolet light techniques (epifluorescence) represent a better semiquantitative geologic approximation of log-derived porosity measurements. However, backscattering of ultraviolet light within the 30-m thickness of a thin section results in overestimation of petrographic void space. Initially, designed for biomedical purposes, the confocal microscope can focus at a single level (approximately 1 m thick) within a standard thin section. As implied by its name, the confocal microscope can quantify images for any depth portion and potentially create a three-dimensional reconstruction of porosity geometry and abundance.
The confocal microscope uses argon lasers to produce degrees of excitation from fluorescent dyes and stains. The intensity of fluorescence in various porosity types varies with the amount of dye imbibed through pore throats into individual pores. Resulting computer-generated images display fluorescence in 256 gray levels on the monitor connected with the confocal microscope. The gray levels can be artificially assigned various colors corresponding to workable categories based on pore morphology. These colors are then quantitatively computed in terms of relative percentages with a specified region or in the entire field of view.
Initial results from formations possessing a multiple porosity system allow quantitative subdivision of total porosity (log-derived and routine core analysis procedures) into percentages of individual porosity types. In some cases, an effective porosity measurement can be obtained and used appropriately in petrophysical approaches and in engineering simulations. The portion of total porosity represented by microporosity, which may bind water, can also be computed.
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Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach,
California, May 5-7, 1993.