Where Are the Trenton-Black River Hydrothermal Dolomite-Hosted Fields of the Illinois Basin?
Hickman, Robert G.
Structural Solutions, Sugar Land, TX,
W. Norman Kent
Kent GeoScience Associates, Richmond, TX,
Mark E. Odegard and Jeff R. Martin
Getech, Stafford, TX
Platform carbonates of the Trenton-Black River (TBR) extend across the northeastern U.S. and adjacent Canada. Recently, gas and oil discoveries have been made in hydrothermal dolomite reservoirs in the TBR of the Appalachian basin, and S. Ontario respectively. Closer to the Illinois basin, similar reservoirs host the Albion-Scipio oil field of the Michigan basin, and parts of the Lima-Indiana field. Are such fields present in the Illinois basin?
These reservoirs formed along reactivated basement-involved faults and fracture zones that served as conduits for saline hydrothermal fluids derived from regional circulation or deep circulation along faults to traverse the low permeability Trenton-Black River. Porosity and permeability were created by solution of carbonate and volume reduction due to the conversion of calcite to dolomite. Oils were derived from distinctive Ordovician source rocks, probably within the TBR and migrated updip via regional aquifers, unconformities and fault zones. Unaltered carbonates and overlying Ordovician shales form the seals.
The elements for development of such fields are present in the Illinois basin. Lack of discoveries may be due to the few TBR tests and targeting of wells toward anticlinal closures rather than flanking, underlying faults. Public domain data are sufficient to model migration of dolomitizing fluids and hydrocarbons. Trenton dolomite reservoirs may occur along minor faults underlying folds of the LaSalle fold belt and along reactivated faults of the Rough Creek-Shawneetown fault zone. Potential fields data can delineate basement-involved faults in favorable migration settings. This allows the seismic data needed to recognize these reservoirs to be acquired in the most prospective areas.