Carbonate Pore-System Analysis Using Ternary Pore Plots

KOPASKA-MERKEL, DAVID C., and STEVEN D. MANN,* Geological Survey of Alabama, Tuscaloosa, AL

Ternary diagrams of carbonate pore types are analogous to the well-known ternary plots of rock composition used to classify sandstones and other kinds of rocks. Ternary pore plots, or TP plots, are constructed from thin-section point-count data using a genetic porosity classification. Apices for TP plots may be assembled from groups of genetically related pore types that collectively account for nearly all pores in a reservoir unit. TP plots illustrate the effects of dissolution, cementation, compaction, and dolomitization on carbonate rock-pore systems. Use of TP plots facilitates recognition of diagenetic processes, gradients, and trends by focusing attention on the distribution of diagenetic products.

The use of TP plots is illustrated by a case study of the Upper Jurassic Smackover Formation in southwest Alabama. More than 75 thin sections of cores taken from a variety of paleogeographic settings were point counted. Three components account for 95% of pores (moldic plus secondary intraparticle, interparticle, and intercrystalline pores). Different reservoir lithofacies within single wells form discrete clusters on TP plots. These clusters correspond to flow units that differ in degree of diagenetic alteration of rock fabric, from interparticle + moldic pore systems (cementation and leaching) through a variety of mixed pore systems to intercrystalline pore systems (pervasive nonmimetic dolomitization). Gradual stratigraphic trends occur within some successions, and can be related t gradients in depositional fabric and in diagenetic intensity (e.g., proportion of primary interparticle porosity). Geographic patterns of pore-type distribution as revealed by TP plots permit recognition of regional pore facies (e.g., particle-moldic facies or intercrystalline [dolostone] facies). Trends and relationships that are clearly apparent on TP plots correspond to conventional core descriptions and to interpretations of commercial core analyses, but are more objectively defined and more readily interpreted.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)