--> --> The origin and timing of CO2 reservoired in the Duperow Formation, Kevin Dome, Montana.

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The origin and timing of CO2 reservoired in the Duperow Formation, Kevin Dome, Montana.

Abstract

Kevin Dome is a large structural culmination along the Sweetgrass Arch in northwestern Montana that produces both oil and gas and has trapped greater than 3 trillion cubic feet (TCF) of CO2 in the Devonian Duperow Formation. The geologic events, timing, and processes that led to the generation, migration, and finally the accumulation of this CO2 are poorly understood. I propose testing three competing hypotheses for the origin of the CO2: (1) CO2 generated from felsic igneous intrusions of the Sweet Grass Hills (~ 20 km northeast) migrated into the Kevin Dome Paleozoic carbonate strata, (2) thermogenic evolution of the underlying Bakken Shale and (3) a mantle-derived source. The work I propose here is part of my broader doctoral dissertation research that seeks to unravel the thermal evolution and sediment source of the Kevin Dome strata and provenance of the CO2 reservoired in its Duperow Formation. I intend to estimate the contributions of the main or multiple source(s) to the origin of Kevin Dome CO2 by constraining the isotopic systematics and pressure-volume-temperature-composition (PVTX) properties of CO2 preserved in Fluid Inclusions (FLINCS) found within the Duperow Formation. FLINCS sufficiently preserve the history of subsurface fluid origin, migrations and filling of reservoirs. Geochemical information and PVTX properties obtainable from them are reliable in evaluating the evolution of fluids in a petroleum system. Therefore, petrographic, geochemical and PVTX analyses on FLINCS will be used to study the origin, relative timing of emplacement, and geologic settings of fluid inclusions (often) trapped in calcite fracture-fill or within rock cement. Confocal Raman spectroscopy will be used to characterize differences in C-O bond vibrations in CO2-bearing FLINCS to differentiate organic versus inorganic CO2 sources. Ultimately, the source of the Duperow Formation CO2 will be compared to the source of CO2 in other natural accumulations in the Rocky Mountains region to understand if they were created from similar sources, related to specific geologic events, or if each accumulation results from unique circumstances. This research is important in aiding our understanding of CO2 origin, migration, rock-fluid interaction, and diagenetic responses. It will establish isotopic geochemistry and PVTX property proxies of fluid inclusions as a reliable technique for fluid origin studies. Furthermore, the study will guide future CO2 provenance studies and explorations for natural CO2 accumulations given the economic values of CO2 for enhanced oil recovery and enhanced coal bed methane recovery processes in the oil and gas industry.