[E&E seminars] Seminar on Marine Methane Hydrates (4/26)

[Karen Gibson]

Please join us Thursday, April 26 at 4:00 pm for a seminar by John  
Grace of Earth Science Associates on marine methane hydrates. These  
hydrates represent a potential future energy resource and modulator  
of climate change.

John D. Grace
Earth Science Associates
April 26, 2007
4:00 - 5:30 pm
E40-496

Methodology for High-Resolution Assessment of
Marine Methane Hydrates in the Gulf of Mexico


John D. Grace,[1] William Shedd,[2] John H Schuenemeyer,[3]
Jesse L. Hunt, Jr.[2] and Gordon M. Kaufman[4]

The concentration of marine methane hydrates (hydrates) in deep water  
along continental margins is a function of three general factors:  
thickness of the net hydrate stability zone (HSZ), the fraction of  
bulk HSZ volume that can be occupied by hydrates and the volume of  
methane charge to the HSZ. Theory and available empirical evidence  
provide ranges of values of variables that determine each of these  
three factors and, in turn, a range of possible volumes of hydrates  
in place.



In order to generate a probabilistic projection of the volume of in- 
place hydrates in the Gulf of Mexico our team built a probabilistic  
model for each general factor and combined them into an omnibus  
probabilistic model of GOM hydrates. With suitable modifications the  
model is applicable to the US Atlantic, Pacific and Alaskan margins.

Net HSZ thickness responds to water depth, geothermal gradient, water  
bottom temperature, proximity to salt and the thickness of the  
sulfate reduction zone below the water bottom, which is a function of  
methane flux through the section. Saturation depends on porosity and  
the ability of hydrates to occupy pore space, both differentiated by  
lithology.

Although both biogenic and thermogenic methane contribute to known  
hydrate exposures on the seafloor of the Gulf of Mexico, biogenic  
methane is assumed to dominate in the shallow subsurface in this  
phase of our work. Due to the complexity of using both thermogenic  
and biogenic charge and due to time constraints, only biogenic charge  
is considered at this time. Biogenic methane production is modeled as  
a function of a modified version of Arrhenius’ Law, scaled to data  
on the productivity of methanogenic archea in the subsurface and the  
influence of water flux (using permeability as a proxy) on  
productivity as it declines with burial. Charge is modeled by  
dividing migration of generated volumes between vertical and dip- 
driven, using the horizontal second derivative of the shape of the  
basement surface to approximate the latter.



Approximately 200,000 2.32 km2 cells cover the area of the Gulf of  
Mexico where water depths are great enough to support hydrate  
formation. The omnibus model produces a probability distribution of  
the total quantity of hydrates in place for each cell. Cell by cell  
probability distributions can be aggregated to larger regions in the  
Gulf or Gulf-wide. An important feature of our approach is that it  
supports high resolution mapping of intermediate and final results.

A probabilistic projection of the fraction of in place hydrates that  
are technically recoverable is supported by our model’s ability to  
provide high-resolution, probabilistic projections of in-place  
volumes. These projections are, in this first phase of the study,  
limited to hydrates in sand and recovery only through pressure  
depletion.

[1] Earth Science Associates, Long Beach, CA.
[2] US Minerals Management Service, New Orleans, LA
[3] Southwest Statistical Consulting, Cortez, CO
[4] Massachusetts Institute of Technology, Cambridge, MA


John D. Grace, Ph.D., a geologist and economist, has specialized over  
a 20-year petroleum industry career on geologic assessment of  
hydrocarbon resources, prospect evaluation and modeling regional oil  
and gas supply. He joined the MMS-academic-industry team assessing  
marine methane hydrates in 2005.


Light refreshment will be provided.
Sponsored by the MIT Laboratory for Energy and the Environment




Karen  L. Gibson
MIT Laboratory For Energy and the Environment
77 Massachusetts Avenue, E40-469
Cambridge, MA 02139  USA
(1 Amherst St., E40-469, Cambridge MA 02142 - for DHL and FedEx)
Tel:  +1 617 258-6368; Fax:  +1 617 258-6590
  
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