Reservoir Characterization of the Mississippian Cypress Sandstone at Lawrence Field Illinois
Beverly Seyler, John Grube, Bryan G. Huff, Curt S. Blakley, and Philip Johanek
Illinois State Geological Survey, Champaign, IL 61820, [email protected]
Detailed reservoir characterization studies of Cypress Sandstone reservoirs at Lawrence Field, a near giant 400 million barrel producer, are being conducted in conjunction with a Department of Energy contract. Cypress Sandstone reservoirs at Lawrence and many fields in the Illinois Basin are complexly compartmentalized. Designing Enhanced Oil Recovery programs that take these complexities into consideration increases the potential for commercial success. Identification of flow units and knowledge of permeability barriers and potential thief zones is important when designing enhanced oil recovery projects. The Cypress Sandstone at Lawrence was subdivided into five sandstone lenses that have been mapped in detail. Cores were described and features that were potential permeability barriers were identified in geophysical logs and used to correlate and map flow units and barriers.
Interpretation of sedimentary structures observed in core includes tidal couplets, flaser bedding, herringbone crossbedding and suggest deposition by tidal processes. The Cypress Sandstone is typically very fine grained and commonly has good porosity and permeability. Cypress Sandstone reservoirs commonly consist of multiple stacked ten foot lenses of sandstone separated by thin intervals of impermeable siltstone or shale. Petrographic examination of reservoir samples shows that the sandstone has intergranular porosity commonly 18% or greater and permeability in the range of 120 md. Sandstones are cemented by quartz overgrowths, the clay mineral suite in pores consist of iron rich chlorite, illite and kaolinite and are likely derived from alteration of feldspars.
AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009