Abstract: An Integrated Geological and Petrophysical Approach to Characterization of the Lawrence Field Ste. Genevieve (McClosky) Reservoirs

Lise Brinton, Michael J. Uland

Reservoir characterization of Mississippian aged (Valmeyeran) Ste. Genevieve "McClosky" subtidal and grainstone shoal carbonates in Lawrence field (Illinois basin), was initiated to identify areas of remaining oil that could be economically produced using infill wells in poorly swept areas of the original 40-acre waterflood pattern. The largest integrated carbonate field study in the Illinois basin, this team effort evaluated geological, petrophysical, and production data for 1000 wells in order to exploit an McClosky reservoirs to their fullest potential. Effective exploitation required an understanding of facies and reservoir heterogeneity through detailed core and petrographic observation, well-log analysis, facies, net-pay and porosity mapping, and production data analysis, to del neate geologically viable and unswept infill areas. Modification of existing depositional and diagenetic models, STRATAMODEL^TM visualization, detailed well correlations, an increased understanding of reservoir distribution and flow-unit connectivity helped identify areas of bypassed waterflood oil. Rw from SP maps aided in identification of waterflood-swept areas by tracking the distribution of freshest injection water. Findings from the project developed 1 million net barrels of oil at a "finding cost" of $1.00/bbl by identifying successful infill zones and targets.

In order to accommodate complex data processing, reservoir and non-reservoir facies characterizing the McClosky were classified differently from earlier studies into three principle stratigraphic intervals: AB interval (four facies distinctions: grainstones, non-grainstones, mixed carbonate-clastic intershoal channel, thin interbedded B dolomudstones), underlying C interval (two facies distinctions: dolomudstone and precursor mudstone), and basal D interval (two facies distinctions: dolomudstone, precursor mudstone). AB grainstones, C and B dolomites are the main reservoir units. Corrensite clay in D dolomite severely degrades reservoir quality. Unswept meniscus cemented grainstones and C dolomites are infill targets.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994