Effect of Isolated Biomoldic Porosity on Log Analysis of Pennsylvanian Carbonate Reservoir, North Texas

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). Either a sonic and/or an electromagnetic propagation tool (EPT) 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 EPT 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 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 the reservoir calculated wet.

AAPG Search and Discovery Article #91026©1989 AAPG Southwest Section, March 19-21, 1989, San Angelo, Texas.