Analysis of Porosity in Lower Ismay Phylloid Algal Packstone Using High-Resolution Computed X-Ray Tomography: ABSTRACT

Abstract

Three-dimensional images of porosity were created using high- resolution computed tomographic (CT) analysis as part of a larger study of phylloid algal packstone from bioherms in the lower Ismay (Des Moinesian, Paradox Formation). The sample imaged was collected at Eight Foot Rapids along the San Juan River in southeastern Utah 40 km west of the Aneth field. The larger study includes analysis of lithofacies, diagenesis, and quantitative analysis of porosity. Our goal is to predictively model porosity in phylloid algal reservoirs. Field observations suggest a relationship between porosity and lithology. Porosity is best established in phylloid algal packstone such as the one chosen for three-dimensional imaging. Locally, porosity is also associated with fractures and stylolitization. Petrographic observations suggest that formation of moldic and vuggy porosity in this sample was controlled by multiple episodes of dissolution and infill of blocky calcite. Porosity in thin section (5.94%) was measured using NIH Image (public domain) on a Macintosh desktop computer. High-resolution CT radiography of a 2.3 cm diameters cm high, cylindrical sample generated a series of 110 images at 0.1 mm intervals. Three-dimensional isosurface images of porosity reveal the degree of interconnection, pore size (up to 12 mm long and from 0.5 mmmore » to 7 mm wide), and their highly irregular shape. These images can also be used to create animations of scans through the rock and three-dimensional, rotating images of the pores.« less