Hurley, Neil F.1, Sherif I. Gowelly2, Teresa Maita3
(1) Colorado School of Mines, Golden, CO
(2) Department of Exploration, Production and Gas Processing, Des Planes, IL
(3) PDVSA, Puerto La Cruz, Venezuela
ABSTRACT: 3-D Analysis of Vuggy Porosity, Indian Basin Field, New Mexico
Indian Basin field produces oil and gas from the Cisco/Canyon Formations (Pennsylvanian) in southeast New Mexico. The reservoir has significant vuggy and intercrystalline porosity developed within algal boundstones, fusulinid grainstone-wackestones, and crinoidal grainstones.
High-energy CT (Computed Tomography) scans at close spacing (0.11 mm) have been run on a 142.75 mm long piece of algal-boundstone core. The same sample was then ground into serial sections. Processing involved: (1) grind rock sample in 1 mm horizontal slices, (2) ink each newly exposed surface with white undercoat and fluorescent orange topcoat, and (3) photograph each inked rock surface under black light. Negatives were scanned, processed, and converted into binary images. Images were converted into SEGY files, then imported into 3-D visualization software. Because of its lower resolution, the CT-scan technique was only able to record 4.7% of the connected vugs seen by the photographic technique.
Whole-core porosity at the depth of interest is 6.0%. After correction for gas content, average log porosity is 8.0%. 2-D analyses of vuggy porosity using arbitrary planes cut through the 3-D volume show that average porosity is 16.6%, with a standard deviation of 3.6%. Average porosity from CT scan images is 6.0%, and average porosity from photographic serial-sections is 13.0%. Part of the discrepancy between porosity measurements is due to the lack of connectivity of some vugs. Also, in this rock, vugs tend to lie flat in the horizontal plane. An analytical model shows that vuggy porosity is higher in horizontal serial sections than in vertical slab faces.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.