Mississippi Lime

The primary productive interval in the section is the Mississippian “Chat”, which comprises the upper 50 to 100 feet in some areas. In this interval porosity has developed as a result of subareal erosion creating a complex mixture of rock types that include chert, limestone and dolomite. This results in lateral and vertical variations in reservoir properties. Production may be driven by matrix properties in some areas, whereas, in other areas fractures play a dominant role. These changes in reservoir properties may have a significant impact on horizontal completion strategies, such as horizontal well directions and the type of stimulation design. Also, water cuts vary regionally, as do initial production rates from horizontal wells (50 boepd to over 500 boepd). There does not seem to be any known oil-water contact.

Where the “Chat” section is absent operators are targeting the Mississippian Lime limestone section. This section has lower matrix reservoir quality but may contain natural fractures. This section requires hydraulic fracture stimulation of horizontal wells for commercial production.

Operators are currently in the process of actively coring the reservoir sections to understand the reservoir complexities. Reservoir characterization and improved formation evaluation techniques are required to optimize the exploitation of this reservoir. Some of the technical challenges to be solved are as follows:

• What is controlling reservoir quality development? Is it related to depositional facies, diagenesis or both? How do these change regionally?
• What are the various reservoir rock types and their petrophysical properties, and how do they vary stratigraphically and regionally?
• What is driving reservoir performance? Matrix permeability vs open natural fractures?
• If fractures are a key in understanding the reservoir, what are the fracture orientation, frequency, spacing, and contribution to permeability?
• With the complexity of this reservoir in terms lithology and porosity development a log petrophysical model needs to be developed based on core data to determine more accurately porosity, water saturation, hydrocarbon pore volume, permeability, water cut (relative permeability), net pay and volumetrics.
• Will the Mississippi Lime and/or “Chat” sections be a candidate for water flood in the future? What primary and secondary recovery can be expected?
• What are the optimal completion and stimulation fluids?
• What is the optimal fracture stimulation design(s) to maximize production?
• How can production performance be predicted to aid in completion decisions?

These problems can only be solved from the geological, petrophysical and completion/stimulation analysis and evaluation of wells with conventional cores. The resultant data can be used to improve 1) reservoir characterization, 2) calibrate open-hole logs in order to better predict rock types and petrophysical properties essential for formation evaluation, 3) proper well completion and stimulation designs, and benchmark production performance. The resultant data sets can also serve as analogs when evaluating new areas in wildcats or field step outs.

Each participating company will be required to contribute conventional core from two (2) wells for analysis and inclusion into the study. All participating companies will share in the project results and interpretations.