Young Carbonate Fabrics as Early Stages in the Development History
of Permian Basin Reservoirs
F. Jerry Lucia Bureau of Economic Geology John A.& Katherine G. Jackson School of Geosciences The University of Texas at Austin
Charting the evolution of pore space through time requires knowing the diagenetic history from the time of deposition until the present. For the Permian Basin this time period is 200600 m.y., and trying to describe this long period of diagenesis using Paleozoic samples has proven difficult. What is needed is direct information about the fabrics at various stages of development. Information on the porosity and permeability of carbonate sediments has been available for some time, and data from limestones and dolostones of Pleistocene, Tertiary, Cretaceous, and Jurassic ages and becoming more available. These data show that porosity destruction is a geologically slow but steady process. Tertiary carbonates with 3040 percent porosity and Cretaceous and Jurassic carbonates with 2030 percent porosity are not uncommon. The data also show that young dolostones tend to have porosity values that are similar to or much lower than their adjacent limestones. Fabric observations of young carbonates and Permian Basin reservoirs suggest that (1) many Permian and Pennsylvanian reservoirs have limestone fabrics similar to those of young carbonates and have lost porosity through simple compaction and cemention, (2) porosity in Permian dolostone reservoirs was inherited from the precursor limestone, reduced by overdolomitization, and preserved from extensive compaction, and (3) Devonian chert reservoirs are porous because the chert replaced a highly porous mud-dominated sediment and inhibited compaction.