Reservoir Characterization of Multiple-Bar Sandstones in the Mississippian Cypress Formation, Tamaroa Field, Perry County, Illinois

Abstract

Tamaroa field produces principally from lenticular sandstones in the upper part of the Chesterian Cypress Formation. These sandstone bodies, interpreted to be marine bars, are typically less than 10 ft thick, 0.25 to 0.5 mi wide,and less than 2 mi long. The bars are vertically stacked and trend northeast-southwest in an en echelon pattern. Spontaneous potential and gamma ray log character, as well as core data, show that shales ranging in thickness from 10 ft to less than 1 ft separate the sandstones. Hydrocarbons are produced from the clean parts of the bars that drape across three structural folds. Multiple structural closures and the stacking of shale-separated bars create discrete reservoir compartments in Tamaroa field. Understanding reservoir compartmentalization is a key factor in designing and infill drilling or waterflood program in a multiple-bar complex such as the one at Tamaroa field. Optimum recovery efficiency therefore can be achieved by using a detailed reservoir model.