Lithofacies and depositional environments of the Cambrian Mount Simon Sandstone in the northern Illinois Basin: Implications for carbon dioxide sequestration

Nicholas E Fischietto, Purdue University

Abstract

Deep saline reservoirs have become a target of increased study with the development of the practice of geological CO2 sequestration. Within the Illinois Basin, the Upper Cambrian Mount Simon Sandstone is being evaluated as a potential reservoir for injected CO2. Because of the depth at which the formation occurs and limited economic interest in the unit it has been only minimally investigated. Previous detailed depositional facies analyses were performed only at local scales or at localities far outside of the Illinois Basin, where the Mount Simon is much thinner and exposed at the surface. In this study, an analysis of existing Mount Simon well cores and geophysical well logs was conducted, resulting in a revised model for the deposition of the unit in the northern Illinois Basin. The Mount Simon is a sub-quartz to quartz arenite that unconformably overlies the Precambrian crystalline basement of interior North America. Core description has led to the identification of several distinct sedimentary facies within the Mount Simon. Coarse, cross-stratified, non-bioturbated sandstone with occasional mud interbedded mudstone and pebble conglomerate comprises the majority of the interval investigated and represents deposition in a braided fluvial environment. Bioturbated, weakly cross stratified sandstone with mud drapes indicates deposition in a tidally influenced braid delta complex, while thinly interbedded, bioturbated siltstone and mudstone represents deposition in a shallow inland sea. Depositional environments interpreted from core descriptions were tied to well logs by comparing logs from the cored intervals to the observed lithofacies. The Mount Simon Sandstone was then divided into seven discrete lithologic/geophysical intervals that were correlated across the northern part of the Illinois Basin and then used in the construction of a series of cross sections and interval isopach maps. In this way, the lithologic intervals best suited for use as a carbon dioxide reservoir can be correlated across the basin. Determination of the depositional facies within this unit and their associated petrophysical characteristics has direct bearing on the ability to predict reservoir performance of the Mount Simon for carbon sequestration.

Degree

M.S.

Advisors

Bowen, Purdue University.

Subject Area

Geology

COinS