Comparison of Petrophysical Characteristics of Selected Carbonate Rocks to Their Log Response, Smackover Formation (Upper Jurassic)

Alfred A. Biehle, M. Carey Crocker

Recent advances in well-logging techniques have enabled geologists to increase their knowledge of petrophysical properties. Optimum use of porosity logs permits predictions of porosity parameters other than merely the porosity percent.

Shallow-water carbonate rocks contain a wide variety of porosity types, and present a special problem to the geologist involved in subsurface work. The oolitic grainstone upper member of the Smackover Formation (Upper Jurassic) within the Gulf Coast region, contains numerous porosity types. Three major types (interparticle, intercrystalline, and oomoldic) were identified from petrographic analysis.

With the use of computer generated crossplots of neutron-log values versus density-log values, it is possible to determine the amount of porosity types within a carbonate rock. The cementation exponent (m) from Archie's equation, as determined from Pickett Plots, is a reliable indicator of the tortuosity and permeability of carbonate units, whereas multivariate cluster analysis groups porosities solely by percent porosity and not by porosity type.

AAPG Search and Discovery Article #91042©1987 GCAGS and GC-SEPM Section Meeting, San Antonio, Texas, October 28-31, 1987.