Gas NMR Characterization of Oil Shale

Eric SorteBrian 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

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

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

• Pore size/structure of interest

OUTLINEI. NMR Overview

II. Gas Diffusion NMR vs. Traditional NMR

III. Experimental Setup/Procedure

IV. What’s Next

Nuclear Magnetic Resonance (NMR)

E

VN S

= ħI

H = - • B = - ħIz Bz

E = ħL where L = Bz

Polarization (I = ½):

T1 ProcessesIn 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.

Mz = Mo ( 1 - exp(-t/T1 ) )

Spin recovers with time constant T1

B1

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?

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

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

ProblemLow densities lead to weak signals

Solutions and advantages

- Shale in situ is pressure fractured with CO2

- Hyperpolarized noble gases

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

Experimental Setup

C2F6

Vcal

V

V

V

V

Probe

V

Imaging Superconducting Magnet

Spoon

Liquid nitrogen bath

Freeze chamber

Oil shale

What’s NextDiffusivity 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 kerogenextraction for conversion to oil**

NMR Imaging

• Precession Frequency Determined by Nucleus and Magnetic Field

T = x B

L = Bz

Pressure Probe and Circuitry

Circuit to match and tune coil to maximize signal