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Controls on Hydrothermal Fluid Flow and Porosity Evolution in the Arbuckle Group and Overlying Units

King, Bradley D.; Goldstein, Robert H.

The Cambro-Ordovician Arbuckle Group has historically been investigated for prolific oil production and is presently a candidate for carbon dioxide (CO2) sequestration in southeast Kansas. Planning for oil production and CO2 sequestration necessitates an understanding of fluid flow and porosity evolution in the Arbuckle Group and overlying units. Integration of transmitted-light and UV epiflourescence microscopy, cathodoluminescence imaging, fluid inclusion microthermometry, and stable isotope analysis helps to establish a paragenesis of the Arbuckle Group and to interpret fluid-flow conduits within and above it, as well as the diagenetic conditions responsible for the reservoir character.

The paragenesis organizes the complex diagenesis of the Arbuckle Group into an early and late-stage sequence of porosity-enhancing and reducing events. Petrographic observations of mineral assemblages suggest relatively late flow of genetically related hydrothermal fluids through the Arbuckle Group and overlying units via fractures and preferred stratigraphic horizons. The mineral assemblage, comparable to MVT deposits (baroque dolomite, mega-quartz, calcite, sphalerite, and galena), indicates the migration of hydrothermal fluids in the past. Results suggest hydrothermal alteration of the extensively dolomitized Arbuckle Group, resulting in possible dissolution and subsequent mineralization. Fluid inclusion homogenization temperatures from late-stage precipitates of the Arbuckle Group yield temperatures ranging from 93-1330C for baroque dolomite and 90-1570C for mega-quartz, values higher than can be explained by burial conditions or an elevated geothermal gradient. Fluid inclusion ice melting temperatures yield salinities ranging from 17.1-20.4 wt. % NaCl equivalent for baroque dolomite and 3.1-6.0 wt. % NaCl equivalent for mega-quartz, values suggesting multiple fluids and evolution through time. Hydrocarbon fluid inclusions in the late-stage baroque dolomite suggest oil migration concurrent with hydrothermal fluid flow. Negative δ13C and δ18O values provide evidence for a basinal fluid source, as well as preferential flow of hot fluids in the upper portion of the Arbuckle Group, where a pore system related to paleokarst is overlain by a regional confining unit. The results of this work illustrate a sequence stratigraphic control on hydrothermal fluid flow, porosity evolution, and oil migration that may be predictable elsewhere.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013