Grants and Contracts Details
Description
Geochemical Analyses of Surface and Shallow Gas Flux and Composition Over a
Proposed Carbon Sequestration Site in Eastern Kentucky
Fractured organic-rich Devonian shale in mature gas fields in eastern Kentucky is being evaluated as a
possible reservoir for carbon sequestration. Injection of C02 into the shale reservoir will produce free
C02 and CH4 gases. Buoyancy forces and reservoir pressurization will provide driving forces for
migration of these gases. Monitoring thus becomes a critical and necessary task in evaluating the fate of
C02 and assessing the efficacy and safety of the sequestration project. The importance of monitoring is
the motivation for this proposal. Specifically we propose to measure and document rates of surface gas
flux and the composition of surface and shallow soil gases in areas overlying possible carbon
sequestration sites in eastern Kentucky. The documentation provides: (1) a database for interpreting the
atmospheric, biologic, and geologic (microseepage) contributions to gas flux pre-injection, (2) a screening
tool for selecting possible sequestration sites, and (3) a background database for monitoring changes in
surface and shallow gas flux and composition that might occur during a sequestration project.
The project will be implemented in three sequential and partly overlapping phases. GIS databases will be
constructed for three previously selected possible sequestration sites during Phase I. The databases will
include GPS coordinates for gas wells in the field, gas monitoring locations (Phase II) and wells (Phase
III), water well and spring locations, gas production histories with an emphasis on gas composition, and
water chemistry data. The GIS databases will be used to spatially analyze the gas production and water
chemistry data, and data generated from monitoring activities in this project.
Phase II work will measure: (1) surface flux of C02 and CH4 using closed chamber methods, (2)
concentration of C02 and CH4 in the shallow soil zone « 1 meter) using gas chromatograph methods
(GC), and the stable isotope (carbon and oxygen) composition of C02 in the soil using mass
spectrometer methods. In an effort to analyze a range of soil gas character, measurements will be
performed in a reconnaissance manner among the three possible sequestration sites. Measurements will
be performed in the summer and winter. Because of reduced biologic input to soil gas flux, winter
measurements will be critical for detecting the subtle geochemical signature of microseepage. Data from
the first year of measurements will be used with other geologic, engineering, and geochemical data, and
cultural considerations in selecting a "best available" sequestration site. Surface and shallow gas
measurements will continue over the "best available" site during the second year of work.
Phase III work be performed in area of the "best available" site during the second year. This work will
examine changes in gas character over a significant vertical soil profile in five wells drilled to 10 meters.
Based on Phase II analysis, the wells will be located in areas that likely do and do not have
microseepage. The goal of Phase III work is to more definitively evaluate the presence of microseepage.
As with the shallow gas work, measurements will be done seasonally and include measuring the
concentration of C02 and CH4 and the stable isotope composition of C02. In addition, the concentration
of light alkanes (C2H6, C3H8) will be measured using GC methods. Light alkanes are often associated
with thermogenic gases and their presence would thus be strong evidence for microseepage. The stable
carbon isotopic composition of CH4 will be measured to look for shifts in gas isotopic composition, which
might signify microseepage. Radiocarbon (14C) measurements of C02 will be conducted on samples
collected during the last sampling. Radiocarbon measurements, expressed in percent modern carbon
(PMC), provide a measure of the degree to which carbon in C02 is young (Le. radiogenically rich) versus
old (Le. radiogenically dead). C02 derived from older geologic sources (Le. microseepage) would be
expected to have low PMC values, whereas C02 derived from soil biologic activity would be expected to
have high PMC values.
Status | Finished |
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Effective start/end date | 7/15/05 → 12/13/08 |
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