Deposition and Diagenesis of the Mt. Simon Sandstone: Unconformities, Basin Analysis, and Anomalous Porosity

Abstract

In Illinois, the Mt. Simon Sandstone has historically been an economically significant target in the gas storage industry and continues to be of valuable interest as the target reservoir for underground injection and storage. With the continued interest in carbon storage, numerous wells have been drilled through the Mt. Simon Sandstone and into the Precambrian Basement significantly broadening our understanding of the geology.

The Mt. Simon is thickest in north to east-central Illinois off-setting the Illinois Basin depocenter in southeastern Illinois. The Mt. Simon Sandstone is divided into three major lithostratigraphic sections: the Lower, Middle, and Upper. A series of sandstones and conglomerates recently named the Argenta Formation, underlies and is believed to be unconformable with the overlying Mt. Simon. The Argenta Formation unconformably overlies the Precambrian igneous basement and is interpreted as shallow marine deposits representing the earliest marine transgression into present day Illinois. The Lower, Middle, and Upper Mt. Simon sections can be further divided into units based on major depositional facies. Major depositional facies in the Mt. Simon include fluvial, eolian, and shallow marine deposits. The Lower Mt. Simon is considered the best reservoir-quality rock with anomalously high porosity and permeability that is overlain by the poorest reservoir quality rock in the tight Middle Mt. Simon. Major diagenetic differences, such as cementation and compaction, differentiate the Middle Mt. Simon from the Lower Mt. Simon and are partly related to an unconformity between the two sections. The Middle Mt. Simon marks the start of the Sauk transgression and possibly Illinois Basin subsidence.

Understanding depositional and diagenetic heterogeneities in the Mt. Simon is necessary for reservoir modeling, characterization, and basin analysis. Further understanding of these heterogeneities is critical in predicting the porosity suitable for injection and geologic storage in the Mt. Simon across the Illinois Basin.

AAPG Datapages/Search and Discovery Article #90218 © 2015 Eastern Section Meeting, Indianapolis, Indiana, September 20-22, 2015