Effect of Isolated Biomoldic Porosity on Log Analysis of Pennsylvanian Carbonate Reservoirs: Case History

Hughbert Collier

Carbonate reservoirs with isolated moldic porosity require more than just routine log analysis (cementation exponent = 2 and a logging suite of dual induction, microlog, density, and neutron logs). A sonic and/or a dielectric tool should be part of the logging package. Both tools are effective in analyzing carbonate reservoirs with moldic porosity, but only if sonic porosities are calculated with the Wyllie equation and the dielectric is used to calculate a "variable m."

This study documents the log analysis of a north Texas well in a Pennsylvanian Canyon limestone with isolated moldic porosity. A thorough logging suite (dual induction, microlog, density, neutron, sonic, and EPT), plus petrographic and SEM analyses of two whole cores, made a number of analytical techniques possible: Productivity Ratio Index and five methods for calculating m. The reservoir appeared to be productive with routine log analysis, but upon further examination it calculated wet.

AAPG Search and Discovery Article #91025©1989 AAPG Midcontinent, Sept. 24-26, 1989, Oklahoma City, Oklahoma.