ABSTRACT Exploration for hydrocarbons in Mississippian strata in Kansas and Oklahoma began in the 1900s. Early production came from open-hole completions in vertical wellbores at the apex of structural and stratigraphic traps. In the mid-20th century, cased-hole completions and hydraulic fracture stimulation allowed development of lower permeability zones. Recently operators began to explore and develop transition zones and low-permeability facies with horizontal drilling. The petroleum system that includes these accumulations consists of two hydrocarbon kitchens in the Arkoma and Anadarko basins, which have been generating oil and gas from the Woodford Shale since the beginning of the Pennsylvanian. Hydrocarbons charged out of the basins and along the fractured terrain of the Cherokee platform into reservoirs from Kinderhookian to Chesterian age across the carbonate facies belt. The distribution of these reservoirs, including limestones, dolomites, and cherts, along with structural configuration, governs the relative abundance and location of oil, gas, and water in each trap. The past decade saw over four thousand laterals targeting Mississippian reservoirs, including shales in unconventional traps, and the greatest rise in oil production in the region since the 1920s. High associated water volumes have created escalating operational costs and are correlative with earthquake activity.

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, δ 18 O 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.

ABSTRACT The St. Joe group (Lower Mississippian, Tournaisian) is petrographically and isotopically analyzed using δ 13 C and δ 18 O bulk sample stable isotopes in central, northeastern Oklahoma, and southwestern Missouri. Determined to be conformable in Oklahoma, this group represents deposition in the mid- to outer-ramp setting during one long-term depositional cycle and can be used as a reference section for geochemical chronostratigraphy. Minor diagenetic alteration did not overprint the initial isotope signal, and the resulting curve is similar to those from previous studies and is integrated with published conodont biostratigraphy. The resulting correlation indicates that the St. Joe group was deposited in the upper Tournaisian Stage.

ABSTRACT Late diagenesis records a common history of fluid flow in sub-Permian strata in the midcontinent, where fluid inclusion Th are higher than burial temperatures and Tm ice show evolving salinity. Most negative δ 18 O dolomite and highest Th are at the top of the Mississippian. Fluid inclusion and geochemical data point to advective fluid flow out of basins utilizing Cambrian–Ordovician–Mississippian strata as an aquifer for hydrothermal fluids. The Pennsylvanian was a leaky confining unit. This system evolved from: Stage 1 Pennsylvanian–early Permian pulsed hydrothermal migration of connate brine and gas; between Stages 1 and 2, low-temperature Permian brine reflux; Stage 2 mixing between high-temperature and low-temperature brines during the Permian; and Stage 3 large-scale migration of hydrothermal brines and oil later during the Permian or after. Stages 1–3 were the most important late processes affecting Mississippian reservoirs, and record an inverted thermal structure with most impact of hot fluids at the top of the Mississippian. Stage 4 shows radiogenic 87 Sr/ 86 Sr in calcite, supporting a transition to localized fault pumping from basement, likely driven by Laramide fault reactivation. Stage 5 is the current system, with Ozark and Front Range uplift-driven fluid flow and potential for small-scale sporadic fault pumping.