EOR Potential of the Michigan Silurian Reefs Using CO2

Abstract

Abstract The Guelph Formation, historically known as the Brown Niagaran, is a Silurian age formation in the Michigan Basin containing hundreds of pinnacle reefs. These reefs, discovered primarily during the 1970s, have produced nearly half a billion barrels of primary oil. Over 700 reefs make up the northern trend and more than 300 reefs have been located in the southern portion of the basin, many of which have produced more than 5 MM bbls of oil. The EOR potential of these fields is believed to be significant. Few of these fields have been waterflooded and only five have experienced CO2 injection. An ongoing US Department of Energy project is studying the use of CO2 in enhanced oil recovery operations at the Charlton 30/31 reef, which is located in Michigan's Otsego County. This field was discovered in 1974 by Shell and produced 2.6 million bbls of oil during its primary production phase from a reservoir that may be typical of the other reefs in these trends. The reservoir is composed of a limestone matrix with low porosity and low permeability that contains irregular dolomitized intervals. These dolomitized zones, with higher porosity and permeability, control the flow of fluids through these reservoirs. This project utilized 4D seismic, reservoir simulation and a new well drilled into the reef to provide greater understanding of the CO2 EOR potential for this and all of the Silurian reefs in Michigan.