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The Illinois State Geological Survey (ISGS) possesses reservoir characterization capabilities that derive from the use of geological and engineering data and techniques including: porosity and permeability measurements, core-flow experimentation, petrography, scanning electron microscopy and energy dispersive x-ray, x-ray diffraction, workstations and computer modeling of geological, geochemical and engineering data. Additionally, a large core and sample library is maintained by the Survey. The ISGS research program to improve and enhance oil recovery in the Illinois Basin utilizes these capabilities and facilities in a multidisciplinary geological and engineering approach to statewide reservoir characterization.

Hydrocarbon production in Illinois has followed a pattern typical of mature basins (fig. 1). Early discoveries were based on surficial geology and resulted in a peak in hydrocarbon production in 1908-1910. The introduction of seismic exploration methods in the late 1930s resulted in significant new discoveries and a production peak in 1940. The application of water-flood technology and hydraulic fracturing during the 1950s led to a lesser production peak in 1956. Since that time, however, production has continued to decline, with minor fluctuations due to variations in the price of oil (fig. 1). The application of improved and enhanced recovery methods could reverse this trend.

The Department of Energy (DOE) has shown in their nationwide analysis that two classes of oil, mobile and immobile, remain in reservoirs after normal production. In I1linois, DOE estimates some 1.5 billion barrels of mobile and 4.5 billion barrels of immobile oil exist in known reservoirs. I1linois ranks ninth in the nation in unrecovered

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