Abstract

The Mississippian limestone of the midcontinent United States is a complex and highly heterogeneous hydrocarbon play. Its heterogeneity is largely due to the mixed siliciclastic and carbonate nature of the midcontinent Mississippian system, which yields complex reservoir lithologies and distributions that are laterally discontinuous and difficult to predict. The purpose of this study is to apply stable-isotope chemostratigraphy, a relatively recent method for addressing industry-related correlation problems, as an additional reservoir characterization tool that provides insight into chemical attributes of Mississippian-aged sedimentation and how these chemical signatures can be used for potential chronostratigraphic applications.

High-resolution sampling (every 0.3 m [1 ft]) of one subsurface core for carbon and oxygen stable isotopes has revealed predictable patterns related to facies and vertical stacking patterns as well as to globally recognized secular changes in ocean chemistry. The chemostratigraphic approach applied herein suggests more frequent third-order cyclicity than recently defined in other subsurface data sets within the basin, which is more consistent with global ties to the individual North American stages and within the Mississippian overall. In addition, δ¹⁸O values suggest a level of predictability at the fourth-order scale related to shallowing-upward packages and mixed meteoric input at cycle tops. Overall, stable isotope curves closely match those of well-established Mississippian global carbon cycling and have been used to suggest time boundaries in this area of the depositional system.