Sense the core

Noninvasive technology to study geological samples

By Salonie Chawla
Published: Tuesday 31 August 2010

imageROCKY layers of earth hold details about geological formations, their history and composition.

The information is particularly valuable for mining companies to ascertain the quantity of minerals present in the earth's crust. To evaluate this, geologists carve out a cylindrical piece of subsurface material, called core sample, by a special drill that works much like an apple corer. While coring is expensive to the tune of tens of millions of dollars, obtaining an unbroken sample, hundreds of metres long is also rare. So core samples are carefully stored for future reference and studies.

But most existing ways of studying the samples involve cutting them into slabs or drilling them. These methods are of high risk to core samples obtained from oil and gas reserves, whose fluid content is unavoidably altered to some extent when cut for exploration. Scientists at energy giant Chevron and technology service provider Schlumberger Oilfield Services in USA have developed a device that helps estimate the amount of oil and gas present in the sample without damaging it. The device uses the anisotropic property of the core, which means in samples with oil the conductivity in one direction, for example, parallel to a layer, is different from that in another, for example, when perpendicular to the layer.

The device is a 60 cm nonconductive fiberglass tube, bent in the shape of a ring, with transmitters and receivers. Once the core sample is placed in it, transmitter induces current in the sample and generates a voltage. The voltage fluctuation can be analysed to ascertain which layer contains oil. "It can make continuous measurements on cores that are hundreds of metres long," lead researcher John Kickhofel noted in Review of Scientific Instruments on July 2. "The device works in the same way as MRI does in human body, without any physical or chemical intervention," said S K Tandon, professor of geology at University of Delhi.

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