Reservoir characterization for the application of ASP flood technology in the Bridgeport Sandstone in Lawrence Field, Illinois

The lower Pennsylvanian Bridgeport sandstone of Lawrence Field, a 400 million barrel mature producing field in southeastern Illinois, is a candidate for enhanced oil recovery (EOR). Detailed reservoir characterization research, supported by a Department of Energy grant, has identified target zones for the alkali-surfactant-polymer (ASP) EOR method. Identification of flow units and knowledge of permeability barriers and potential thief zones are critical to the success of this EOR project Mapping efforts identified distinct flow units in the northern part of the field showing that the Bridgeport consists of a series of thick incised channel fill sequences. The sandstones are about 75-150 ft thick and typically consist of medium grained and poorly sorted fluvial to distributary channel deposits at the base. The sandstones become indistinctly bedded distributary channel deposits in the main part of the reservoir before fining upwards and becoming more tidally influenced near their top. These channel deposits have core permeabilities ranging from 20 md to well over 1000 md. The tidally influenced deposits are more compartmentalized compared to the thicker and more continuous basal fluvial deposits. Fine grained sandstones that are laterally equivalent to the thicker channel type deposits have permeabilities rarely reaching about 250 md Cores were described and potential permeability barriers were correlated using geophysical logs. Petrographic analyses were used to better understand porosity and permeability trends in the region and to characterize barriers and define flow units. Diagenetic alterations that impact porosity and permeability include development of quartz overgrowths, sutured quartz grains, dissolution of feldspar grains, formation of clay mineral coatings on grains, and calcite cementation. Many of these alterations are controlled by facies Lawrence Field is unique in terms of the scale and the application of ASP flood technology and the success of the project would encourage similar EOR projects in comparable fields around the world.