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Methane transport in agricultural soil after injection of isotopically-enriched methane in the sub-surface.

ABSTRACT: Small quantities of radioactive methane (14CH4) may be released over prolonged periods from geological disposal facilities for radioactive waste. The impact of this release depends on the capacity of soil to oxidise 14CH4 to 14CO2 during transport from the sub-surface to the atmosphere. We investigated this capacity by pulse-injecting isotopically-enriched methane 50?cm below the surface of an agricultural soil in central England. Three sequential injections were made during growth of a spring wheat crop. Samples of gas were taken from the pore space throughout the soil profile at predetermined time points after injection, accompanied by samples of the atmosphere above the soil collected in sampling chambers, deployed at scheduled intervals. Methane and CO2 were measured in soil and above-ground gas using gas chromatography; the isotopic composition of CH4 and CO2 was determined using gas chromatography with isotopic ratio mass spectrometry. Supporting measurements of environmental variables were made during the experiment. The data can be used to test mathematical models describing CH4 and CO2 transport and fate in temperate agricultural soils.

SUBMITTER: Shaw G

PROVIDER: S-EPMC6190747 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature

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Methane transport in agricultural soil after injection of isotopically-enriched methane in the sub-surface.

Shaw George G Atkinson Brian B Meredith William W Snape Colin C Lever David D Hoch Andrew A

Scientific data 20181016

Small quantities of radioactive methane (14CH4) may be released over prolonged periods from geological disposal facilities for radioactive waste. The impact of this release depends on the capacity of soil to oxidise 14CH4 to 14CO2 during transport from the sub-surface to the atmosphere. We investigated this capacity by pulse-injecting isotopically-enriched methane 50 cm below the surface of an agricultural soil in central England. ...[more]

PMID: 30325354

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Project description:Carbon dioxide (CO2) is both a primary greenhouse gas and a readily available energy source. In this study, a new underground coal permeability enhancement technique utilizing cryogenic liquid CO2 (L-CO2) cyclic injection is proposed. The key parameters that determine the feasibility of this technique are cycle period and cycle number within a fixed working period. The optimal value of these two parameters mainly depends on the pore structure evolution law of coal cores before and after cryogenic L-CO2 cyclic freeze-thaw. Accordingly, nuclear magnetic resonance (NMR) was employed to study the evolution characteristics of the fracture networks and pore structures in coal cores subjected to different freeze-thaw cyclic modes. The results demonstrated that the amplitude and width of all peaks of the T2 spectra of the three coal cores (lignite, gas coal, and 1/3 coking coal) increased with an increase in the number of injection cycles. Additionally, as the number of freeze-thaw cycles (Nc) increased, the total porosity and effective porosity of the coal cores increased linearly before stabilizing, while the residual porosity first steadily diminished and afterwards became constant. Furthermore, the variation in the total porosity and residual porosity of the coal cores continuously diminished with an increase in the level of metamorphism. The NMR permeability of the coal cores showed a similar pattern to the porosity. Accordingly, the optimal parameters for cryogenic L-CO2 cyclic injection during a complete working time were determined to be Nc = 4 and Pc = 30 min. A field test demonstrated that after L-CO2 cyclic freeze-thaw treatment, the average gas drainage concentration of a single borehole in the test region increased by 1.93 times, while the pure flow of a single gas drainage borehole increased by 2.21 times. Finally, the gas attenuation coefficient decreased from 0.036 to 0.012. We concluded that the proposed permeability enhancement technique transformed coal seams from hard-to-drain to drainable.

Project description:RationaleInformation on the isotopic composition of nitrous oxide (N2 O) at natural abundance supports the identification of its source and sink processes. In recent years, a number of mass spectrometric and laser spectroscopic techniques have been developed and are increasingly used by the research community. Advances in this active research area, however, critically depend on the availability of suitable N2 O isotope Reference Materials (RMs).MethodsWithin the project Metrology for Stable Isotope Reference Standards (SIRS), seven pure N2 O isotope RMs have been developed and their 15 N/14 N, 18 O/16 O, 17 O/16 O ratios and 15 N site preference (SP) have been analysed by specialised laboratories against isotope reference materials. A particular focus was on the 15 N site-specific isotopic composition, as this measurand is both highly diagnostic for source appointment and challenging to analyse and link to existing scales.ResultsThe established N2 O isotope RMs offer a wide spread in delta (δ) values: δ15 N: 0 to +104‰, δ18 O: +39 to +155‰, and δ15 NSP : -4 to +20‰. Conversion and uncertainty propagation of δ15 N and δ18 O to the Air-N2 and VSMOW scales, respectively, provides robust estimates for δ15 N(N2 O) and δ18 O(N2 O), with overall uncertainties of about 0.05‰ and 0.15‰, respectively. For δ15 NSP , an offset of >1.5‰ compared with earlier calibration approaches was detected, which should be revisited in the future.ConclusionsA set of seven N2 O isotope RMs anchored to the international isotope-ratio scales was developed that will promote the implementation of the recommended two-point calibration approach. Particularly, the availability of δ17 O data for N2 O RMs is expected to improve data quality/correction algorithms with respect to δ15 NSP and δ15 N analysis by mass spectrometry. We anticipate that the N2 O isotope RMs will enhance compatibility between laboratories and accelerate research progress in this emerging field.

Dataset Information

Methane transport in agricultural soil after injection of isotopically-enriched methane in the sub-surface.

Publications

Methane transport in agricultural soil after injection of isotopically-enriched methane in the sub-surface.

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