Oil potential seen in Silurian reef-related reservoirs in Illinois Sangamon arch

Patch reef reservoirs have been identified in the lower Racine sequence in the northeastern part of the Mount Auburn trend in Sangamon Arch, Illinois Basin. The Mount Auburn trend, situated along the southern flank of the Sangamon arch, consists of a number of oil fields and covers portions of Macon and Christian counties in west-central Illinois. The reservoirs of the lower Racine in the Mount Auburn trend are porous dolomitized coral reef or reef rudstone facies in the upper part of the lower Racine sequence. The reef and reef rudstone facies comprise coarsely crystalline dolomite containing poorly preserved fossils and skeletal molds of reef-building organisms with intercrystalline and moldic porosities of up to 25%. The reservoir facies are of limited lateral and vertical extent that can reach a total thickness of up to 30 feet and is made of the upper part of meter-scale, shallowing-upward cycles.