Geological and Petrophysical Characterization of the Lawrence Field, East-Central Illinois, for Alkaline-Surfactant-Polymer Flooding
The giant Bridgeport Anticline in Lawrence County, Illinois, a subsidiary four-way closure on the LaSalle Anticline, has produced in excess of 400 million bbls of oil since its discovery in 1906. Original oil in place (OOIP) has been estimated at 1 billion barrels, leaving about 60% of the OOIP as a potential tertiary recovery target. Based on Marathon Oil Company field trials in the 1980’s, recent radial core flood tests, and two proof-of-concept pilot floods currently underway, an additional 15-30% of the OOIP might be recoverable using alkaline-surfactant-polymer flooding technology.
The present integrated study was undertaken to evaluate reservoir characteristics and heterogeneity in advance of field scale flooding. The primary reservoir zones of interest are the U. Mississippian Cypress (average depth 1400 ft), comprising discontinuous marine and tidally dominated deltaic sandstones averaging 19.5% porosity with permeabilities ranging from about 70 - 800 mD; and the Pennsylvanian Bridgeport (average depth 900’), a fluvial-deltaic-estuarine sandstone system averaging 21.5% porosity with permeabilities ranging from 90 - 1400 mD.
The Bridgeport is lithologically heterogeneous with the lower units (Buchanan, Bridgeport A, Bridgeport B) comprised of fluvial and estuarine valley-fill sandstones; whereas the upper Bridgeport C-D-E units are thinner, more discontinuous and lenticular sandstones deposited in a variety of shallow estuarine and bay fill settings. The Cypress is also lithologically heterogeneous with the Lower Cypress dominated by prograding tidal channel sandstones and shales overlain by Middle Cypress deposits comprising mainly tidally dominated distributary channel sandstones and interdistributary silts and muds.
Detailed well log correlations using digital and raster logs from ~4900 wells, logged from the 1930’s to present, allowed high resolution definition of the principal sequence boundaries and major flooding surfaces, particularly in the Bridgeport section, over a 42 sq mile project area. Within each defined paleovalley system, e.g. the Bridgeport B, there are multiple erosional surfaces and sand fills associated with migrating channel systems. In most places the sandstones are physically separated by shales or by tight cemented zones and flood patterns will be designed to optimize sweep within individual compartments.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009