Abstract

Phylloid algal carbonate mounds are abundant through most of the Pennsylvanian-Permian stratigraphic section in the Permian Basin, and often form significant hydrocarbon reservoirs. Petrographic analysis shows the mounds contain fossils of other common shallow-marine biota including bryozoans, bivalves, echinoids, and fusulinids.

Phylloid algae had aragonitic skeletal structures similar to the modern calcareous green algae Halimeda. Aragonite is highly susceptible to diagenesis by meteoric waters. Diagenetic alteration is an important factor that controls the reservoir quality of phylloid algal mounds. Most of the porosity within phylloid algal mounds is secondary and is principally moldic.

Structure and isopach maps of the Upper Pennsylvanian carbonate deposits of the Northwest Shelf of the Permian Basin in Southeastern New Mexico show a relationship between the paleo-structure of underlying units and the deposition of these carbonate deposits. Petrographic analysis of core samples shows at least three distinct petrofacies including dolomites, biomicrites, and biosparites. In addition to multiple petrofacies, petrography has revealed varying degrees of porosity development and reduction. Porosity is dependant upon the degree of occlusion by calcite cement.