Another interesting fact about the Mississippian is that it is a limestone and not a shale, meaning it is not self-sourcing. Almost all of the oil and gas present in the Mississippian was sourced by the Woodford Shale (a world class source rock) which then traveled long distances and was trapped by the stratigraphy in the Mississippian (examples of which are illustrated below).
As a result of this, the Mississippian has a greater variability between wells of whether it produces oil, gas, or oil and gas. This can lead to sometimes surprising well results in areas where there is sparse vertical well control. Often times, these accumulations can change very rapidly in producing phase with areas going back and forth between predominantly oil to predominantly gas. You can even have situations where you intersect an oil reservoir followed by a gas reservoir in the Mississippian due to the nature of how the oil and gas is trapped. Thankfully, due to the thousands of vertical wells, it is possible to map areas in the play where oil accumulations are more prevalent than gas and calculate statistical probabilities. Geologists can also determine which rock types are present allowing for a better understanding of rock properties and depositional environments.
As horizontal drilling continues along the borders of Kansas and Oklahoma, it will be interesting to see how the play continues to grow as companies learn about this play.