New Approaches to Experimental Studies of Hydrocarbon-Water Reactions

A recent study documented the stability ranges of the three crystal structures of methane hydrate at room temperature.

figureReactions between water and hydrocarbons have a major impact on the distribution of hydrocarbon in Earth, but fundamental aspects of their reactions and products have not been studied systematically. At low temperature and high pressure, methane and other low-molecular weight hydrocarbons can form hydrates, some of which are widely distributed on and beneath the seafloor at water depths greater than 800 m.  The recent study by a team of scientists from China and the U.S.A., including the Carnegie Institution of Washington and the U.S. Geological Survey (USGS), documented the stability ranges of the three crystal structures of methane hydrate at room temperature. This paper has set the stage for a next series of experiments to document hydrate stability over a wider range of temperature and pressure conditions.

At temperatures above those reached in the above study, particularly at temperatures at the upper stability limit of petroleum (~250C) and higher, hydrocarbon-water reactions may involve oxidation-reduction reactions that generate or destroy hydrocarbons, but these reactions have not been systematically investigated either.  To better understand these reactions, two types of optical cells were recently developed at the USGS; a new type of hydrothermal diamond-anvil cell (type V; Fig. 1) for experiments at P-T conditions near the Moho and a fused silica capillary capsule technique for P-T conditions in the crust (Fig. 2).  The latter technique is readily applied to studies of hydrocarbon pyrolysis and thermochemical sulfate reduction (TSR). Such optical cells allow studies of reaction mechanisms and kinetics with microbeam techniques such as laser Raman spectroscopy.  New optical techniques are currently being evaluated by USGS scientists for chemically specific three-dimensional imaging of experimental systems and natural samples.  Results of these investigations will improve understanding of reaction kinetics at phase boundaries and reactive transport of hydrocarbons in the deep Earth. This type of experimental work will be an important part of planned research to be conducted with support of the Deep Carbon Observatory.

The studies can be found online at:

Shu et al., Geosci. Front. 2, 93-100 (2011)
Chou et al., Goldschmidt Conf. Abstr. A178 (2010) and references therein
Chou et al., Geochim. Cosmochim. Acta 72, 5217-5231 (2008)
Shang et al., Geochim. Cosmochim. Acta 73, 5435-5443 (2008)
I-Ming Chou and Robert C. Burruss, U.S. Geological Survey, Reston, VA 20192

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