Kirsten M. Bannister¹, Brian D. Keith², Todd A. Thompson³

(1) Dept. of Geological Sciences, Indiana University, Bloomington, IN
(2) Indiana Geological Survey, Indiana University, Bloomington, IN
(3) Indiana University, Bloomington, IN

ABSTRACT: Building a Reservoir Characterization Model of a Carbonate Shoal, Salem Limestone (Middle Mississippian), South-Central Indiana

Sawed exposures of the Salem Limestone (Mississippian, Valmeyeran) shoal facies in quarry walls offer an opportunity to develop a model of a grainstone reservoir. Fluid pathways in a carbonate reservoir are controlled by the distribution of porosity and permeability, which are in turn related to the distribution of cement types in carbonate grainstones. Through petrographic analysis of the Salem, the control of cement and grain type distribution over porosity and permeability can be documented. In addition, the distribution of primary porosity and permeability can be recognized from cement histories.

The distribution of different grain types in the Salem is closely linked to the different hierarchical levels of bounding surfaces that define bedform geometries within the shoal. Vertical and lateral variation of grain types and textures are best observed along and between foreset laminae (first-order surfaces). Dominated by echinoderm grains, the coarsest grain-flow foresets have the highest variation in porosity and permeability. Micritized foraminifera and bryozoan grains dominate the thinner, finer-grained, grain-fall foresets, which exhibit increasing porosity and permeability down the slope of the foreset. Grain compositions do not vary significantly across erosional bounding surfaces between bedforms (second- and third-order surfaces), but distinct increases in grain size and reduced packing effectively enhance porosity and permeability along these surfaces. Contacts between facies in the shoal (fourth-order surfaces) are characterized by variations in grain types, an increase in microcrystalline calcite cement, and common pressure solution between grains that lowers porosity and permeability.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado