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SNR Targets "Viola" Trenton Ordovician Carbonate Play

All production from this play has been from fossiliferous limestones of the Champlainian-Cincinnatian Galena Group ("Trenton"). Reservoir thickness ranges from 12 ft in the Woburn Consolidated field, Bond County, Illinois, to 140 ft in the Clark County division, Clark County, Illinois. There has been minor gas production tests from the Trenton along the eastern edge of the Embayment in Calloway County, Kentucky, but there are no fields that are of the minimum size for assessment. Gas has also been recovered from a drillstem test of the Thebes Sandstone Member of the Maquoketa in Crittenden County, Kentucky, which is located roughly 20 mile northeast of the Mississippi Embayment. Most Trenton reservoirs are characterized by primary, intergranular porosity (grainstone/rudstone) enhanced by fractures (Duquoin Monocline) ranging to entirely fractured reservoirs with minimal porosity (LaSalle Anticline).

Most zones of secondary porosity developed several tens of ft below the top of the Galena within a porosity fairway trending southwest-northeast through the central part of the basin that may be related to paleogroundwater flow patterns developed during the formation of the sub-Tippecanoe (latest Ordovician) unconformity. Porosity zones within the interval have been seen in Green County, Indian, however there is no known production from this zone. Another zone of porous dolomite is located in Jackson County, Illinois, in the vicinity of the Cottage Grove fault system. Other secondary porosity reservoirs are possible as discontinuous dolomite horizons within limestone located in the southern and central parts of the Illinois Basin and as regional dolostones in the northern parts of the basin. Reservoir quality is quite variable with porosity ranging from 6 to 12 percent and permeability from 2 to 320 mD although these values may grossly underestimate the reservoir properties within zones of secondary porosity. Other possible reservoirs, other than the Trenton reservoirs within the play are suggested by: (1) production tests of oil recovered from fractured High Bridge carbonates along the Rough Creek fault zone in Webster County, Kentucky; (2) drill-stem tests of oil and gas from the Fort Atkinson Limestone (Maquoketa) of the western shelf in western and northwestern Illinois; and (3) oil saturated cores taken from the Thebes Sandstone (Maquoketa) in southwestern Illinois.

Read More About our Targeted Plays within the Illinois Basin Here.

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