History of hydrothermal fluid flow in the midcontinent, USA: the relationship between inverted thermal structure, unconformities and porosity distribution

Abstract

AbstractA comprehensive study of the Cambrian–Ordovician Arbuckle Group suggests that multiple fluid migration events have affected reservoir porosity via fractures and preferred stratigraphic horizons. Fluid inclusion homogenization temperatures from late-stage precipitates yield temperatures higher than can be explained by burial conditions or an elevated geothermal gradient. Fluid inclusion melting temperatures yield salinity values that indicate multiple fluids evolving through time. Hydrocarbon fluid inclusions in late-stage baroque dolomite suggest oil migration concurrent with hydrothermal fluid flow. Depleted δ13C and δ18O values provide evidence for a high-temperature basinal fluid source as well as for the preferential flow of hydrothermal fluids through permeable zones in the Mississippian and Arbuckle Group, where pore systems related to paleokarst are overlain by less permeable units. Radiogenic strontium isotopic data support fluid–rock interaction with siliciclastic material or basement rock at some point during the fluid migration history. Variable 87Sr/86Sr values suggest multiple sources for the fluids responsible for the cements and a transition from an advective fluid flow system to a vertical fluid flow system. The ancient aquifer system was vertically connected during migration of hydrothermal fluids, and a temperature-controlled vertical density gradient appears to have played an important role in late-stage porosity evolution, focusing the hottest fluids in the upper sections of permeable layers.