Use of earth field spin echo NMR to search for liquid minerals

Patent · Mon Jan 01 00:00:00 EST 2001

OSTI ID:873510

Stoeffl, Wolfgang ^[1]

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1. Livermore, CA

An instrument for measuring the spatial, qualitative and quantitative parameters of an underground nuclear magnetic resonance (NMR) active liquid mineral deposit, including oil and water. A phased array of excitation and receiver antennas on the surface and/or in a borehole excites the NMR active nuclei in the deposit, and using known techniques from magnetic resonance imaging (MRI), the spatial and quantitative distribution of the deposit can be measured. A surface array may utilize, for example, four large (50-500 diameter) diameter wire loops laid on the ground surface, and a weak (1.5-2.5 kHz) alternating current (AC) field applied, matching the NMR frequency of hydrogen in the rather flat and uniform earth magnetic field. For a short duration (a few seconds) an additional gradient field can be generated, superimposed to the earth field, by applying direct current (DC) to the grid (wire loops), enhancing the position sensitivity of the spin-echo and also suppressing large surface water signals by shifting them to a different frequency. The surface coil excitation can be combined with downhole receivers, which are much more radio-quiet compared to surface receivers, and this combination also enhances the position resolution of the MRI significantly. A downhole receiver module, for example, may have a 5.5 inch diameter and fit in a standard six inch borehole having a one-quarter inch thick stainless steel casing. The receiver module may include more than one receiver units for improved penetration and better position resolution.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• DOE Contract Number: W-7405-ENG-48
• Assignee: Regents of University of California (Oakland, CA)
• Patent Number(s): US 6177794
• OSTI ID: 873510
• Country of Publication: United States
• Language: English

Related Subjects

earth
field
spin
echo
nmr
liquid
minerals
instrument
measuring
spatial
qualitative
quantitative
parameters
underground
nuclear
magnetic
resonance
active
mineral
deposit
including
oil
water
phased
array
excitation
receiver
antennas
surface
borehole
excites
nuclei
techniques
imaging
mri
distribution
measured
utilize
example
50-500
diameter
wire
loops
laid
ground
weak
5-2
khz
alternating
current
applied
matching
frequency
hydrogen
flat
uniform
duration
additional
gradient
generated
superimposed
applying
direct
dc
grid
enhancing
position
sensitivity
spin-echo
suppressing
signals
shifting
coil
combined
downhole
receivers
radio-quiet
compared
combination
enhances
resolution
significantly
module
inch
fit
standard
six
one-quarter
thick
stainless
steel
casing
units
improved
penetration
resonance imaging
inch thick
wire loop
magnetic resonance
direct current
magnetic field
stainless steel
alternating current
nuclear magnetic
surface water
ground surface
field applied
wire loops
position sensitivity
receiver antenna
diameter wire
phased array
underground nuclear
including oil
improved penetration
mineral deposit
active nuclei
active liquid
surface receive
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