The goal of this project is to apply a multi-component, multi-dimensional reactive transport simulation code to constrain modern day methane fluxes and to reconstruct past episodes of methane flux that can be correlated with environmental changes.
Oregon State University – Corvallis, OR
The importance of understanding the role that gas hydrates play in the global carbon cycle and their potential as a future energy resource has long been recognized and is a key component of the Methane Hydrate R&D Program. Fundamental questions remain, however, as to the residence time of gas hydrates near the seafloor and deeper within the sediment column, the sources and pathways of methane transport, nature and driving mechanisms for flow, and changes in these variables over time.
In order to better understand these fundamental dynamics of methane in present and past environments, Oregon State University will model the complex nature of these interactions by adapting a comprehensive kinetic transport-reaction model based on the CrunchFlow code (Steefel, 2009) to simulate the processes occurring in the sediment column (diagenesis, sediment burial, fluid advection, and multi-component diffusion) and estimate net seafloor fluxes of solutes. CrunchFlow is a software package for modeling and simulation of reactive flow and transport through porous media including groundwater aquifers, soils, sediments, and crystalline rocks. The software can be used to simulate a range of important processes and environments, including reactive contaminant transport, chemical weathering, carbon sequestration, biogeochemical cycling, and water-rock interaction. CrunchFlow is available as a free download. The user's manual for CrunchFlow is available below under "Additional Information".
Development of a set of user-friendly CrunchFlow-based geochemical modules, tested and implemented using readily available field data (e.g., Cascadia, India, Ulleung Basin), will result in a more complete set of proxies to reconstruct changes in methane flux over time. A coherent set of simulation tools can be used in an integrated approach for future field projects such as those being proposed for the Arctic margin and other high methane flux sites and climate sensitive gas hydrate-bearing regions worldwide.
A complete kinetic model describing the biogeochemical cycling around the sulfate-methane-transition-zone has been formulated. The model accounts for changes in the concentration and isotopic profiles of various dissolved and solid species.
The kinetic model was applied to pore water data collected from eight sites drilled during the second Ulleung Basin gas hydrate drilling expedition (UBGH2) in South Korea in 2010. The model revealed very different biogeochemical environments between acoustic chimneys (three sites) and non-chimney sites (five sites). Organic matter decomposition is an important process for production of methane, dissolved inorganic carbon and consumption of sulfate in the non-chimney sites while anaerobic oxidation of methane (AOM) predominates both carbon and sulfur cycles in the chimney environment. AOM, mediated by methane, occurs in both settings however, the model revealed different sources of methane between the two settings. At non-chimney sites the internally produced methane (i.e., produced through CO2 reduction and methanogenesis) fuels AOM while in the chimney sites external sources of methane are required to support AOM.
OSU extended the Crunch Flow model to account for the precipitation/dissolution of authigenic barite. Records of authigenic barite distribution in the sediments can be used to infer the depth of sulfate-methane transition zone (SMTZ), which can be linked to the strength of methane flux in the past. The model results indicated that methane produced through methanogenesis was insufficient to account for the observed barite records in the Cascadia Margin and that additional methane from an external source is required (i.e., methane inflow from outside the model regime). Further, the model results indicate that this external pulse of methane occurred between 75.7 ka and 33 ka. This corresponds to a period of time bounded by two theorized slope failure events suggesting that the high methane flux was likely the result of sediment disturbance by slope failures.
Krishna-Godavari Basin, India
Using pore water profiles of sulfate and ammonium from sediments recovered during the 2006 Indian National Gas Hydrate Project (NGHP-01) expedition, OSU was able provide quantitative estimates of the thickness of individual mass transfer deposits (MTDs), the time elapsed after the MTD event, rate of sulfate reduction in the MTD, and time required to reach a new steady state. Model results suggest that the MTDs are 8 to 25 meters thick and 300 to 1600 years old. Within the MTD sections, sulfate reduction rates are 126 to 1215 mmol/m2yr; this reflects a much thicker sulfate reduction zone as a result of these MTDs compared to other regions.
A preliminary version of this model was tested with biogeochemical data collected from the K-G basin in India.
The kinetic model was applied to pore water data collected from eight sites drilled during the second Ulleung Basin gas hydrate drilling expedition (UBGH2) in South Korea in 2010. The model revealed very different biogeochemical environments between acoustic chimneys (three of the eight sites) and non-chimney or background sites (the remaining five sites). While anaerobic oxidation of methane predominates both the carbon and sulfur cycles in the chimney environments, organic matter decomposition is an important process for production of methane and dissovled inorganic carbon, and for the consumption of sulfate in the non-chimney sites. These modeling results have been submitted as a draft manuscript to Geochemica et Cosmochimica Acta.
The project is complete. The final report is available below under "Additional Information".
The results of this effort help to constrain the biogeochemical processes occurring in the sediments near the SMTZ and are important from a research perspective with regard to the role of methane hydrate in global greenhouse gas emissions and climate change. The project resulted in two submitted manuscripts:
Final Project Report [PDF-10.5MB] January, 2014