The Mississippi Lime (Mississippian) is a difficult, altered lime reservoir with significant secondary porosity that produces oil in Kansas and Oklahoma. Variations of this reservoir also produce in many other areas of North America. Production generally is from horizontal well bores and has a very high water cut. Using conventional log analysis to characterize oil vs. water is difficult because resistivity can be the same for both fluid types. In addition, compartmentalization is common in this reservoir so oil can be located above and below any water.

The ability to decrease the water cut can make significant changes in the economic outlook of any set of completion decisions. Thus, Nuclear Magnetic Resonance (NMR) logs were added to the evaluation program because of their unique ability to discern different fluid types by measuring polarization, or T1. This measurement can be a fairly direct indication of fluid type and in most instances, can deliver a usable assessment of reservoir fluids. When combined with the relaxation, or T2 measurement from the same device, very accurate fluid type descriptions can be obtained. This data is measured in vertical wells and used to target lower water saturation portions of the reservoir.

In addition, apparent permeability can be determined from the Bray-Smith permeability equation. This provides a useful estimate of rates that may be expected from potential intervals. This data, combined with fluid typing, allows for targeted drilling and completion in the most hydrocarbon productive portions of the Miss.

This paper summarizes the application of this technology application in the Mississippian and demonstrates how increased oil cut and decreased water cut can be achieved in this complex reservoir.