Gas NMR Characterization of Oil Shale

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Gas NMR Characterization of Oil Shale
Eric Sorte Brian Saam Gernot Laicher
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Oil Shale

• Fine sedimentary rock, contain kerogens
• Estimated 2 trillion barrels of oil in shale
  reserves in Wyoming, Utah, Colorado 400 year
  supply
• Extraction of oil involves pressurized pyrolysis
  and/or solvent processes of reactive chemicals
• Research goes back more than a century
• According to a survey conducted by the RAND
  Corporation, crude oil extraction is unlikely
  to be profitable unless crude oil prices range
  between US70 to US95 per barrel.

Bartis, James T. (2005). "Oil Shale Development
in the United States. Prospects and Policy
Issues. Prepared for the National Energy
Technology Laboratory of the U.S. Department of
Energy. The RAND Corporation. ISBN
978-0-8330-3848-7 Retrieved on 2007-06-29.
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Why Study Oil Shale

• Pore size/structure of interest

• Characterize rock at each stage of chemical
  treatment,
• sequentially removing internal matrix and
  revealing structure

• Changes of porosity/structure as function
• of pressure and temperature

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OUTLINE

• NMR Overview
• Gas Diffusion NMR vs. Traditional NMR
• Experimental Setup/Procedure
• Whats Next

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Nuclear Magnetic Resonance (NMR)
N
S
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T1 Processes
In equilibrium, magnetization lies along z-axis
It is possible to change the net magnetization
by exposing the nuclear spin system to energy of
a frequency equal to the energy difference
between the spin states.
B1
Spin recovers with time constant T1
Mz Mo ( 1 - exp(-t/T1 ) )
We can characterize porosity, permeability,
tortuosity, and surface to volume ratios once we
know T1
- R.L. Walsworth - Dean O. Kuethe
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Why Gas Diffusion NMR?
Problem
Low densities lead to weak signals
Solutions and advantages

• Weak signal overcome by multiple spins per atoms
  (C2F6)

• Inert fluorinated gases have very short
  relaxation times (signal avg.)

• Densities 1000 lower than liquids allow
  exploration of small porous
• regime where diffusive displacement is on order
  of pore size

• Shale in situ is pressure fractured with CO2

• Hyperpolarized noble gases

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Experimental Setup
V
Spoon
Vcal
Imaging Superconducting Magnet
V
C2F6
Freeze chamber
V
V
V
Probe
Liquid nitrogen bath
Oil shale
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Whats Next
Diffusivity studies on raw shale
Characterize rock at each stage of chemical
treatment, sequentially removing internal matrix
and revealing structure
Determine pressure, temperature dependence
Understand fluid flow in shale under different
conditions
Find simple, cheap, low-impact method of
in-situ kerogen extraction for conversion to oil
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NMR Imaging
T ? x B

• Precession Frequency Determined by Nucleus and
  Magnetic Field

? L ? Bz
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Pressure Probe and Circuitry
Circuit to match and tune coil to
maximize signal