Gas NMR Characterization of
Oil Shale
Eric Sorte
Brian Saam
Gernot Laicher
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 US$70 to US$95 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.
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
OUTLINE
I.
NMR Overview
II.
Gas Diffusion NMR vs. Traditional NMR
III. Experimental Setup/Procedure
IV. What’s Next
Nuclear Magnetic Resonance
(NMR)
N
S
V
Polarization (I = ½):
 =  ħI
H = - • B = - ħIz Bz
E = ħL where  L =  Bz
E
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
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
Experimental Setup
V
Spoon
Vcal
Imaging Superconducting Magnet
V
Freeze chamber
V
V
V
Probe
Oil shale
Liquid nitrogen bath
C2F6
What’s 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**
NMR Imaging
T=xB
• Precession Frequency Determined by Nucleus and
Magnetic Field
 L =  Bz
Pressure Probe and Circuitry
Circuit to match and tune coil
to maximize signal