St. Louis — Sophisticated new remote sensing techniques are taking oil exploration back to its roots. This is just one way in which the ability to identify materials at a distance is revolutionizing oil and mineral exploration.
At the turn of the century, oilmen drilled at places where oil leaked to the surface. But the development of seismic methods - detonating surface explosions and measuring the reflected sound waves - supplanted the old approach because it allowed petroleum geologists to detect underground traps where oil is likely to accumulate.
Now, companies like Recon Exploration in Dallas have begun mounting sophisticated instruments called spectrometers in helicopters to locate minute quantities of hydrocarbons that can seep to the surface from as deep as 20,000 feet underground.
''Using this approach we have had over a 50 percent success rate on wildcat drilling,'' Dr. C. Keith Thompson of Recon reported at the annual meeting of the American Chemical Society, being held here this week.
The spectrometer divides light reflected from the ground into a large number of colors, or wavelengths. Then it measures the intensity of light in each of these color bands. Because each material has a unique spectral signature, scientists are able to detect minute amounts of hydrocarbons. And they have found that in many cases this corresponds with underground reservoirs of oil and natural gas.
Since the National Aeronautics and Space Administration launched the first earth resources satellite, Landsat 1, in 1972, it has proved particularly valuable in oil exploration, says G. Bryan Bailey of the US Geological Survey (USGS).
Although the original satellite was not designed with geology in mind, it had a spectrum analyzer that broke reflected light down into four broad color bands. This, combined with the panoramic view from space, gave geologists a unique tool that they have exploited to study broad geological structures. This has proved particularly useful for oil exploration, Dr. Bailey says.
Since then, four more Landsats have been launched, each with improved instruments that have provided greater detail for geologists in government, academia, and private industry to use.
Another geological use for remote sensing from satellites and aircraft is exploration for hard-rock minerals. Geophysical and Environmental Research Inc. (GER) is a New York company that specializes in this type of work.
''While the satellites have a few bands, we build custom instruments with hundreds of bands,'' William Collins of GER explains.
Mounting such instruments in a helicopter or airplane allows them to make detailed measurements of the chemistry of the surface below.
''Take gold, for instance. There is a characteristic clay associated with gold deposition. It doesn't look special even to a geologist. But our instruments pick it out quite well,'' Dr. Collins explains.
Most of their work is proprietary, so the scientist cannot talk about it. But his company surveyed Death Valley for the USGS and found a previously unknown geologic formation rich in silver and molybdenum.
Exploration of this sort has so far been largely confined to desert areas because the ground can be surveyed directly. Trying to figure out what is in the earth beneath a covering of thick vegetation is much more complicated. But here, too, steady progress is being made.
An example of this is work being done by E. A. Guinness of Washington University in St. Louis. He has been studying Landsat photos of southern Missouri and has found that the canopy of oak and hickory growing over granite areas look brighter in the infrared than it does when the trees are growing in softer, sedimentary rock areas.
''I don't have any idea what accounts for this difference,'' the scientist admits.
But the experts do know that the growth of trees and plants can be subtly effected by the mixture of minerals in the soil where they grow. (Another high-tech method of prospecting for gold is to collect material from plants and send them to a laboratory where they are analyzed. Plants growing in gold-rich areas pick up minute quantities of the precious metal, and this can be detected.)
With his custom-built spectrometers, Dr. Collins can detect evidence of certain metals in light reflected by vegetation. Lead, copper, and zinc, for instance, alter plants spectral signature because they are toxic. ''We have used this to map ore deposits in Montana and Appalachia,'' he says.
But the scientists say lack of information about how various plants interact with minerals in the soil makes this approach much chancier than prospecting in arid areas.
Those involved in remote sensing for mineral exploration have mixed feelings about President Reagan's plan to turn the Landsat system over to private enterprise. Currently, the administration is evaluating seven such proposals, which it solicited, and should be announcing a decision on them within a few months.
''For the purpose of our industry, it doesn't pay to spend $10 million to put an instrument in orbit. You can buy quite a bit of aircraft time for that sum,'' Collins says.
Another problem with the geological remote sensing, Thompson and he agree, is that instruments flown in space have not been optimized for their specific needs because they have been designed for a number of other purposes as well, such as crop inventorying.
''There is a need for both private and public satellite remote-sensing data worldwide,'' argues USGS's Bailey. ''If we don't do it, someone else will.''
Already the West Germans have developed an advanced spectral scanner, which they have flown on the shuttle, that can pick out features as small as 60 feet across.
The French have developed a similar system that has stereoscopic capability.
''We need a publicly supported system to push and improve the technology,'' Professor Guinness adds.
Despite the satellites, helicopters, and all the other fancy equipment, the scientists involved don't think the day will come when geologists will forsake the trusty hand pick they use to break apart interesting looking rocks for examination.
Remote sensing is not a substitute for on-the-ground surveys or drilling. But these techniques can direct field crews to the most promising locations, saving considerable time and money.