Controls on dolomitization of the Upper Ordovician trenton limestone in south-central Kentucky
The Late Middle Ordovician Trenton Limestone is a highly productive carbonate hydrocarbon reservoir across the eastern United States. Enhanced secondary porosity and permeability within the Trenton Limestone generated by hydrothermal dolomitization (HTD) in Michigan and New York have allowed for extensive hydrocarbon reservoirs to be developed. In these areas, carbonate facies assemblages have been shown to significantly control the distribution of diagenetic alterations and influence the geometry and lateral continuity of reservoir-grade porosity and permeability. South-central Kentucky provides an exploratory region for post-depositional hydrothermal alteration due to its vicinity to the Appalachian-forming orogenic tectonism. Cool water carbonate deposition of the Trenton in Kentucky provides for a new setting composed of facies assemblages that are significantly different when compared to warm water carbonate hosts of the Trenton in New York, Ohio, and Michigan. Results from outcrop and core analyses indicate that HTD is not facies-selective as the abundance of phosphate and marine hardgrounds in Kentucky’s cool water carbonates are porosity-destructive. Rather than primary facies, controls of dolomitization through central Kentucky consist of a combination of fault and fracture networks, fluid injection pressures, homogenization temperatures, and basement fluid sources and sub-Trenton carrier beds. Dolomitization through the Trenton is characterized by vugular, interparticle, intraparticle, and fracture porosity, which are frequently restricted to near-fault and fracture margins. Investigation of fluid inclusion microthermometric and stable isotope analyses indicate that fluids are sourced from deep Precambrian or Cambrian formations. Fluids generally range from 127°C to 107°C indicating that they are in fact hydrothermal (maximum burial temperatures of 80°C through the Cincinnati arch region; Huff and Turkmenoglu, 1981) and have variable fluid compositions ranging from saline brines to NaCl-H2O-CaCl2. Results of this study indicate that Kentucky provides for a setting that is highly susceptible to hydrothermal dolomitization and subsequent reservoir development, however cool water carbonates through the Trenton Limestone are not conducive to allow for reservoir-grade porosity and permeability development. The lack of depositional phosphate within warm water carbonates of the underlying Black River Group Carbonates does, however provide for a valid target to explore for HTD reservoir development in central Kentucky.^
Gray, Collin James, "Controls on dolomitization of the Upper Ordovician trenton limestone in south-central Kentucky" (2015). ETD Collection for University of Texas, El Paso. AAI10000785.