THE OVERSIMPLIFICATION OF THE MID-CONTINENT MISSISSIPPIAN

A recent trend in increased hydrocarbon exploration in Mississippian-aged carbonates in the Mid-Continent Region has showcased the need for more detailed facies distribution maps and depositional models. Much of the current work is based upon earlier models (1980’s) that do not capture the degree of facies variability and distribution that is common in carbonate systems. Additionally, many of the earlier models do not incorporate paleogeography or the structural history of the region. Evaluation of modern carbonate systems indicates that a high degree of facies variability should be expected in the types of systems most commonly applied to the Mississippian in the Mid-Continent (i.e. ramp, distally steepened ramp or rimmed shelf). In addition, eustatic and relative sea level changes impacting the region necessitates that facies maps should be developed in “time-slices” that capture the migration of the system during regional transgressions and regressions.

A new model is proposed that considers observations from different scales of exploration and compares their varied results with the scales of facies distributions in modern carbonate systems. The proposed conceptual model integrates the documented relationships between bathymetry, dominant wind/current directions and the distribution of facies in modern carbonate systems. The proposed model describes a single “time-slice” with the understanding that there are several “time-slices” in the Mississippian interval. Knowing that each time slice could have a slightly different facies distribution, a better understanding of the variations in facies mosaics can be obtained. The facies variability in this conceptual model is realistic for a carbonate system and helps to explain how wells spaced 660’ apart can have drastically different facies in cores and logs. Through incorporation of modern analogs, this conceptual model explains complexities observed in Mississippian carbonates and could immediately impact the success rates of exploration and production programs in this complex reservoir.