Elk Basin Madison Heterogeneity Its Influence on Performance

The 920-ft thick Madison limestone of Mississippian is one of the 7 producing horizons in the Elk Basin field, located on the Wyoming-Montana border near Yellowstone Park. Full section coring, done nearly 20 yr after the horizon was discovered and after more than 65,000,000 bbl oil had been produced, has shown the reservoir rock to be distorted highly by ground-water erosion, solution, and remineralization that took place at the end of Mississippian deposition. Geologic interpretation of the new data has helped to define reservoir discontinuities and to explain anomalies previously noted in reservoir performance, and has provided a better basis for analyzing current performance. An improved understanding of reservoir heterogeneity led to a development drilling program which has increased production from 16,000 bopd to a peak rate of 24,600 bopd. Waterflood efficiency also has been improved by adjusting injection water distribution to account for difference is subzone performance and for discontinuities.