Validation and sensitivity analysis of gas ebullition prediction by biogenic gas fracture mechanics theory
Abstract
Gas ebullition from cohesive sediments results primarily from biogenic methane production at rates sufficient to cause bubble nucleation, sediment fracture, and bubble growth and rise. Our previous work has determined that gas ebullition can mobilize sedimentary pollutants to the water column at rates greatly exceeding other release mechanisms. Biogenic gas fracture mechanics theory (BGFMT) is a mechanistic model of gas ebullition based on linear elastic-fracture of sediment in response to porewater transport of biogenically produced gas. According to BGFMT, gas production kinetics and sediment strength play key roles in controlling gas ebullition in cohesive sediment. However, the relative impact of environmental factors on overall process kinetics is not clear. Thus, our objective in this research is to quantitatively assess the impact of model parameters on BGFMT-predicted gas ebullition.
Our approach to achieve this objective is to perform a Global Sensitivity Analysis (GSA) on all parameters that contribute directly or indirectly to bubble formation in the BGFMT model. In GSA, all biogeochemical parameters are varied simultaneously within the defined threshold ranges for cohesive sediment, which can then be used to assess the interaction of these parameters as well as their individual contribution to output variance. For validation of BGFMT, a large homogenized pool of test sediment was used in experiments to measure sediment properties and biogenic methane production rate. We then measured evolved gas from sediment columns of various depths in the laboratory to assess gas ebullition rate and compared results to BGFMT model predictions. Together, these experiments allow us to elucidate the impact of gas production biokinetics, confining pressure, and sediment mechanical properties on gas ebullition rate and determine the relative importance of these parameters by sensitivity analysis. These results can then be used to focus field characterization efforts to predict ebullition kinetics and guide remedial efforts.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H31J2054K
- Keywords:
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- 1829 Groundwater hydrology;
- HYDROLOGYDE: 1831 Groundwater quality;
- HYDROLOGYDE: 1832 Groundwater transport;
- HYDROLOGYDE: 1847 Modeling;
- HYDROLOGY