FY2010 - Oak Ridge National Laboratory

Seed Money Fund—
Materials Science and Technology Division
05882
Using Small Angle Neutron Scattering (SANS) to Determine Gas
Hydrate Pore-Scale Distribution
Claudia J. Rawn, Gernot Rother, Kenneth C. Littrell, Tommy J. Phelps, and William F. Waite
Project Summary
Understanding the pore-scale distribution of methane hydrate formed within sediment is crucial to safe
energy extraction. The laboratory synthesis of sediment samples containing methane hydrate that closely
mimic those found in nature is a key challenge to furthering scientific understanding of how methane is
geologically accommodated. Hydrate in nature is likely to occur as pore fill, in contrast to laboratory
samples, where hydrate more commonly cements sediment grains together. These differing distribution
scenarios result in vastly different mechanical properties. We hypothesize that small angle neutron
scattering (SANS) experiments on gas hydrate and sediment mixtures can be used to accurately determine
the distribution of gas hydrate and sediment. These experiments are challenging to conduct in situ due to
the pressure, temperature, and time requirements needed for hydrate formation, thus requiring a proof of
principle prior to proposing a full study for the anticipated DOE Office of Science initiative in gas hydrate
research.
Mission Relevance
Gas hydrates are solid, crystalline structures in which water molecules arrange to form polyhedral cages
large enough to hold low-molecular-weight molecules. These low temperature, modest pressure
compounds occur in continental margin and terrestrial permafrost sediments where there are adequate
sources of H 2 O and hydrate-forming molecules (usually alkanes, and most commonly, methane). Gas
hydrates are of interest from both economic and environmental standpoints, first as a potential source of
natural gas and second as a reservoir of greenhouse gases (methane and carbon dioxide). Understanding
the pore-scale distribution of methane hydrate formed within sediment is a variable crucial to the safe
energy extraction and prediction of greenhouse gas releases resulting from climate changes.
The U.S. Geological Survey (USGS) is also a major player in the area of gas hydrates research. USGS
scientists as well as scientists in academia, the gas and oil industry, and other national laboratories will
use our results.
Results and Accomplishments
The account funding this project was opened on June 24, 2010. The focus of the project to date has been
to build a system to use with the existing SANS pressure/temperature cell. The system was designed to
deliver methane through one port, H 2 O/D 2 O mixtures through a second port, have a vacuum connected to
a third port, and pressure transducer to the fourth. Most of the components to build a stand-alone system
that could be portable to various SANS beamlines (e.g., CG2 in the cold guide hall of the High Flux
Isotope Reactor at ORNL or one of SANS instruments at the National Institute of Standards and
Technology) were ordered and received by September 30, 2010. In addition to the new components, an
existing syringe pump was refurbished and software was written to control the pump and to track the
water flow needed to keep the system at a constant pressure. A proposal for general user beamtime on the
CG2 SANS at ORNL was written and submitted for consideration.
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