Reservoir Characterization for an Alkaline-Surfactant-Polymer Flood of Mississippian Cypress and Pennsylvanian Bridgeport Sandstone Reservoirs in Lawrence Field Illinois

By

GRUBE, JOHN P., BEVERLY SEYLER, BRYAN G. HUFF, and CURT S. BLAKLEY

Illinois State Geological Survey, 615 East Peabody Drive, Champaign, IL 61820 [email protected]

     Research results from a Department of Energy-sponsored alkaline-surfactant-polymer (ASP) pilot flood in Future successful hydrocarbon exploration in the Ste. Lawrence Field, Illinois will be described. Of the estimated 0.7 to 1.0 billion barrels of original oil in place in Lawrence Field, over 330 million barrels of oil have been produced from shallow Middle Mississippian Cypress and Lower Pennsylvanian Bridgeport sandstone reservoirs. Presently, oil cut is less that 3% for this 96 year old field. A successful full field, seven sq. mile, ASP flood has the potential to recover 42 million barrels of oil. A thorough understanding of the reservoir is necessary to realize this potential.

     Cypress Sandstone reservoir architecture at Lawrence Field, as well as at many other Illinois oil fields, is characterized by multiple 10 to 40-foot thick, vertically stacked or shingled sandstones. These sediments were originally deposited in shallow marine environments including tidal shoals and linear sand ridges.  Oriented northeast-southwest, the ridges are commonly isolated and compartmentalized.

     Detailed reservoir characterization of the Pennsylvanian Bridgeport A, B, and D sandstones in a 60 acre pilot area shows that rapid facies changes are responsible for compartmentalization of Pennsylvanian reservoirs. Facies interpretations based on core from six new wells in the pilot area show that these reservoirs are thin, fluvial-deltaic and shallow marine deposits. Evidence from detailed core descriptions, and mapping and modeling of facies architecture show that the porosity, permeability and reservoir quality are closely associated with the distribution of discrete sedimentary facies. Effective implementation of secondary and tertiary recovery strategies need to address compartmentalization and the aerially limited, facies-related differences in reservoir quality.

     Petrographic analysis of reservoir rocks and chemical analysis of reservoir oils show there are major mineralogic, diagenetic and chemical differences between the reservoir rocks and oils in the Bridgeport and Cypress reservoirs. Special attention to reservoir compartment geometry and proper chemical formulation of floods are required for optimal recovery from these reservoirs.

Note

     Bridgeport and Cypress core from the Lawrence Field pilot area and Cypress core from other fields will be on display for viewing and discussion in the Exhibit Hall following this presentation.