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High Resolution Sequence Stratigraphy and Reservoir Characterization of the Mississippian Lime in Northeastern Oklahoma


Mississippian limestone reservoirs are significant unconventional hydrocarbon reservoirs in central and northern Oklahoma and southern Kansas that are found at relatively shallow depths (3,000-6,000ft). Over 14,000 vertical wells have been drilled in the Mississippian Lime reservoirs, but recent activity has focused on developing the reservoir using horizontal drilling methods. Despite historic and recent drilling activity, little is understood about the properties and distribution of many of the productive Mississippian reservoirs. Detailed facies analysis suggests deposition on a regionally pervasive, distally steepened carbonate ramp. Facies stack into shoaling upwards packages consisting of weakly calcareous mudstones to wackestones at the base, followed by progressively higher energy, traction-dominated facies. The sequence stratigraphic hierarchy of the Mississippian Lime can be defined as an overall 3rd order sequence (100's of meters thick) containing 4th order high frequency sequences (10's of meters thick) and 5th order cycles (few meters thick), which form due to variations in relative sea level. The stratigraphic hierarchy plays a major role in controlling the overall quality and vertical heterogeneity of the reservoir units. Core and thin section analyses demonstrate that the Mississippian Lime is characterized mostly by fracture and moldic porosity, and that the highest porosity intervals exist in the higher energy traction current facies. Preliminary interpretations suggest that reservoir quality may be controlled by the 4th order high frequency sequences. Impermeable mudstones associated with these high frequency cycles likely cause vertical compartmentalization of the reservoir. Incorporating a detailed sequence stratigraphic framework into the reservoir characterization and 3D seismic interpretation of the Mississippian Lime provides an enhanced understanding of the complex lateral and vertical variability of subsurface reservoir facies, and may lead to better reservoir prediction at the exploration and production scales.