Large scale natural gas emplacement traced by noble gases: the Virunga Volcanic Province
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Date
2015-05
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The Ohio State University
Abstract
Enhanced oil recovery (EOR), sometimes called tertiary recovery, involves the injection of miscible fluids such as carbon dioxide (CO2) into previously produced hydrocarbon reservoirs. EOR commonly prolongs the life of petroleum reservoirs globally, in some instances nearly doubling the amount of petroleum initially recovered with conventional methods and water flooding. As a result, today, carbon dioxide reservoirs with sufficient volume and pressure to provide EOR fluids are a resource that is in an increasingly high demand.
For these reasons, the development of geochemical techniques, capable of better characterizing the source and the history of CO2 reservoir filling, trapping, and producible volumes is critical to the future economic success of EOR and the petroleum industry in general. In order to explore successfully for economically viable CO2 fields, one needs to understand the sources, emplacement history, and subsequent tectonic evolution of a CO2 reservoir. These factors can be determined by understanding the magmatic source of CO2 gases, the isotopic composition of the CO2 gas, the stratigraphic and structural conditions of reservoir trapping, and the volume of CO2 that is present in reservoirs today.
The Virunga Volcanic Province (VVP), located along the western branch of the East African Rift System (EARS), provides an example of a currently filling CO2 reservoir. As a result, it represents an appropriate place to study the source, migration, and emplacement of CO2 reservoirs and validate many currently applied geochemical techniques. Throughout the last forty years, the Virunga Volcanic Province has experienced intense volcanic activity, which has led to significant interest in volcanic hazard activity in this region. For this project, we examined the major and trace element geochemistry of volcanic products and fumarole gases to evaluate the source and emplacement of CO2 into the Earth's crust in the VVP. This study provides a comprehensive dataset of gas geochemistry for potential magmatic and geothermal sources, isotopic tracers of subsurface CO2 migration, reservoir infilling, and water-gas interactions. Specifically, my data include major gas compositions (CO2, N2, O2, H2), noble gases (abundance and isotopic composition such as (e.g., 3He/4He, CO2/3He, CH4/3He, 40Ar/36Ar, 40Ar*/4He)), and stable isotope geochemistry (δ13C-CO2) from fumaroles on Mount Nyiragongo and throughout the region to evaluate the sources that feed magmatic systems across the VVP and major and trace element data for a time series of lava samples taken from Nyamuragira (2006 and 2010 eruptions) and Nyiragongo (2002 eruptions and lava lake samples from 2005 and 2010).
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Keywords
noble gas, Nyiragongo, carbon dioxide, CO2 reservoir, emplacement history, Virunga Volcanic Province