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:

"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 to answer."

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 Inc.

Stambaugh authored a paper last spring for the Oil and Gas Journal on the potential benefits of NMR tools.

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 tissue."

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, were possible.

"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 be."

Step-by-Step

Basically, NMR logging involves three steps, Stambaugh said.

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 technology are:

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 permeability information.

"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 permeability.

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:

"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 their laurels.

"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 clear sample.

"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."

Looking Ahead

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, Gubelin said.

"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 evolve quickly.

"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 identification.

"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."