The petroleum industry is a business
built on pushing the technological envelope, and today one
of the cutting edge technologies that is changing the face
of well logging is NMR, or nuclear magnetic resonance.
A lot of people might know that is happening,
but not many know exactly how - or why. In fact, the very
words "nuclear magnetic resonance" can humble oil company
personnel with anything less than a Ph.D. in physics.
But that might be changing.
NMR experts are getting better in pointing
out how the enormous benefits this technology brings to
the table make the time and effort to understand and apply
NMR worth the effort. Not surprisingly, NMR is beginning
to hit its stride in the industry as more and more companies
recognize the information this tool provides that cannot
be acquired with any other technique.
"Our colleagues in the industry are basically
looking to answer four questions in a reservoir," said Dave
Marshall, manager of reservoir description for NUMAR, a
product service line within Halliburton Energy Services.
Those questions are:
What's the storage capacity or porosity?
Is there a method by which those fluids can be delivered?
In other words, is there permeability?
What kind of fluids are going to be delivered?
If hydrocarbons are delivered, will there be any water
delivered as well?
"The NMR tool has the ability to answer all
four questions," Marshall said. "Many people see the technology
as extremely complex, but in reality it can answer all the
questions that for years it has taken a whole array of tools
As Greg Gubelin, NMR products manager with
Schlumberger, said, "Answers from NMR are used by the petrophysicist,
geologist and completion and reservoir engineer as an innovative
way to cut coring and testing costs and to optimize completion
strategies and reservoir production."
A Successful Decade
NMR techniques were first studied as early
as the 1950s with the first attempt at commercial use in
1961 - but those early attempts used the earth's magnetic
field, which is rather weak, so they were not wildly successful,
said Brian Stambaugh, president of Houston-based NMR Petrophysics
Stambaugh authored a paper last spring for
the Oil and Gas Journal on the potential benefits of NMR
Schlumberger first became involved with NMR
measurements in the 1960s when the company licensed a tool
that was developed by Chevron.
"We designed a next generation tool that
was used in the 1970s and 1980s," Gubelin said, "but it
was with the advent of pulsed acquisition NMR in the early
1990s that the industry was able to take that quantum step
with the technology."
The 1990s marked NMR's rebirth.
"Initially the technology was very slow,
which was a drawback," Stambaugh said. "But in the early
1990s there were some successes using NMR tools in East
Texas and on the Gulf Coast where conventional formation
evaluation was difficult."
Those successes opened the development door.
"Industry began to see that NMR provided
textural information on the rock," Stambaugh said, "much
like medical MRIs provide textural information of human
NUMAR developed a mandrill type tool in the
early 1990s that employed a permanent magnet and a single
radio frequency, which provided effective porosity measurements
that were lithology independent as well as a bulk volume
irreducible component of porosity, according to Charley
Siess, MRIL product manager with NUMAR.
"That's about all the tool provided in the
early 1990s," Siess said, "and it was exceedingly slow,
with operating speeds of about one foot per minute."
About that same time Schlumberger designed
its new tool that allowed the firm to increase the logging
speed and get a more accurate measurement of complete formation
porosity, Gubelin said.
By 1995 the next generation of NMR tools
were developed, employing multiple frequencies. These tools
achieved operating speeds of up to five feet per minute
and allowed for clay porosity in the measurements, which
meant total porosity measurements, not just effective porosity,
"Also, with the new tools we were able to
start recording multiple wait time measurements and multiple
echo spacing measurements," Siess said. "These new measurements
allowed NMR to move into new and different applications."
By 1997-98 NMR was becoming a primary formation
evaluation instrument and consisted of nine operating frequencies
with increased operation speeds.
"With these new developments we could now
in a single pass do dual wait times and echo spacing measurements
for direct hydrocarbon typing, as well as obtain all the
fundamental reservoir properties achieved with earlier versions
of the technique," Marshall said.
"We have finally reached the point where
we can run NMR tools at as high a logging speed as possible
while keeping the quality of the data as high as it can
Basically, NMR logging involves three steps,
First, a permanent magnet aligns or polarizes hydrogen
nuclei and this polarization involves an exponential
Second, a transmitted radio frequency field manipulates
the nuclei. Each radio frequency pulse "flips" the nuclei
and after each flip, energy returns to the antenna or
receiver coil as spin echoes.
Finally, after the radio frequency pulsing terminates,
the nuclei realign with the permanent field during the
Gubelin spoke of NMR's two key functions:
"We actually measure the response from the
fluids in the pore space of the rock, so we get what's known
as a mineralogy independent porosity," he said. "Also, NMR
measurements give operators a producibility answer in which
the porosity is broken down into its constituent parts -
bound and free fluids - to get a measurement of how the
formation will produce."
The two key applications for NMR logging
Reservoir characterization, including total and effective
porosity, bound and free fluid volumes, permeability,
pore size distribution and clay characterization.
Fluid characterization, which encompasses direct hydrocarbon
typing or detection.
Stambaugh said log results are presented
as NMR field log, integrated saturation analysis products
and fluid identification from NMR.
The NMR field log generally includes NMR
total and effective porosity, bound fluid or free-fluid
volumes and permeability. It may also include quality control
curves. The integrated saturation analysis logs uses resistivity
analysis to determine whether the free-fluid volume contains
hydrocarbons or water.
Marshall said the technology's most important
advancements have been in the areas of improved permeability
derived measurements as well as direct hydrocarbon typing.
"NMR is the first tool that allows us to
directly measure permeability," he said. "Prior to the advancement
of this technology whole core was the only means to get
"Today we can directly correlate NMR downhole
measurements with core laboratory measurements," he continued.
"The significance of this correlation is we can make any
petrophysical measurement we want in the laboratory and
then take those measurements to gather the same type of
information with the downhole tool, thereby building a model
to use directly for the downhole tool to measure permeability.
"Prior to NMR technology there was never
a reliable way to directly tie core laboratory permeability
measurements with measurements from the logging tool."
Ron Bonnie, NUMAR Team One senior NMR research
and applications scientist, said NMR is the only technology
currently available that measures the pore size distribution
of a sample and pore size distribution is what determines
NMR technology provides four direct hydrocarbon
identification and saturation techniques, according to Stambaugh.
The technique used depends on the tool, the formation evaluation
problem and the amount of time available for logging, as
well as other factors.
The four techniques provided are:
Time domain analysis uses data recorded at two different
polarization times for light hydrocarbon typing and
Density magnetic resonance compares NMR porosity to
density porosity for gas identification.
The shifted spectrum technique uses multi-echo spacing
data and is applicable in certain light-oil viscosities.
The enhanced diffusion method uses a dual wait time
with longer inter-echo spacing to enhance the oil signal's
visibility and is used in direct fluid identification
of light oils.
"For these methods to work properly there
must be some amount of residual hydrocarbon available for
measurement in the sensed volume of the NMR devise," Stambaugh
said. "This eliminates formations with low gas pressure,
low porosity or complete flushing."
Plenty of Work Waiting
While NMR technology is beginning to catch
on throughout the industry, developers are not resting on
"Our NMR program is guided by our customer
feedbcack," Gubelin said, adding that Schlumberger meets
"regularly with NMR experts in our customers' organization's"
to identify problems and needs.
Schlumberger is currently introducing its
CMR Plus tool that, while maintaining the features of the
CMR tool, has improved on three key features: three to five
times faster logging speed, better data precision through
improvements in tool hardware (the magnet, the electronics
and acquisition), and the capability of logging in slimholes
as small as 5 7/8 inches.
"In a recent well in the North Sea where
the logging interval was about 1,000 feet, we completed
the logging process in a little less than an hour," Gubelin
said - a saving of about four hours.
"The savings in rig time alone was more than
$30,000," he added.
"Also, we are currently investigating deeper
depth of investigation measurements, and it's our philosophy
to transport all wireline measurements onto the drill pipe,
so we are working on an NMR while drilling tool."
NUMAR's Siess said that "next year NMR-WD
(while drilling) will be available to oil companies ...
(which) will provide all the traditional NMR applications
and information - but it will provide that information while
drilling the borehole as well as supplemental measurements
in the sliding mode, or measurement after drilling mode."
This new technique will not only provide
the standard T2 measurement - the amount of time it takes
for the magnetization component to deteriorate and which
always has been available with NMR - but also a T1 measurement,
which is the amount of time it takes for the magnetization
component to occur.
"Also, NMR while drilling allows us to take
NMR measurements early in the process, before the affects
of invasion," he said. "Plus, NMR-WD, like any measurement
while drilling technique, provides time and cost savings
to a project."
Another technological advancement scheduled
for commercial use in 2001 is a magnetic resonance fluids
analyzer. This instrument will be part of a new reservoir
description tool and will essentially make laboratory quality
T1 type measurements in reservoir conditions.
For example, he said, an institute in France
that monitors the quality of wines made all over the country
has acquired a few NMR spectrometers. They run the wines
through the spectrometer and can not only tell which winery
the wine is from but whether the grapes were grown on the
north flank of a mountain or the south flank.
"This technology is that much more discriminating
than optical analyzers," he said.
Marshall said NUMAR has been preparing a
catalog of mud filtrates to use for comparative purposes
in conjunction with the new magnetic resonance fluids analyzer.
The intent is to take measurements on fluids
as they come into the formation test tool, monitoring the
change and very clearly determine when we are at optimum
"Ultimately this should lead to directly
providing measurements of viscosity and gas-oil ratio,"
Marshall said, "which in turn can be incorporated into a
company's producibility and rates predictions, how they
set facilities and what type of facilities they set."
Continuing technological advancements and
education make the future for NMR tools very bright.
"We continually work with clients to show
what NMR can do," Siess said. "Typically, after they see
the benefits for themselves they are sold. But, honestly,
it has taken more time than any of us anticipated to educate
the industry on the advantages."
NUMAR recently established a team approach,
providing a group of experts to help clients determine objectives
and define how NMR can help.
Gubelin said Schlumberger did the same.
"We have a network of experts," he said.
"This group's chief responsibilities are making sure every
job is properly pre-planned, acquisition and interpretation
is handled correctly, and to follow-up with customers."
The company has done about 4,000 NMR loggingjobs
in the last four years, from China to the North Sea to Venezuela,
"The service companies are unwavering in
their belief of the power of this tool," Siess added. "Halliburton
(is) aware that it will take time to establish the fundamental
change in thinking that will lead to common use of NMR tools,
and every day we work on new ways to cross the chasm with
this new technology."
Stambaugh said all the major service companies
have large staffs focused on NMR, so this technology should
"NMR is by no means fully developed," he
said, adding that there will be "major improvements" in
areas such as better bed resolution and advances in fluid
"We must continue to advance the technology,
prove the value of the measurement and deliver complete
service," Gubelin said, "and NMR will reach its full potential."