Now, a detector to distinguish 'sour' oil from 'sweet'

In what could help the crude oil exploration and production companies to zero in on a clear oil fields, scientists have now created a nanoreporter, a device to detect the presence of hydrogen sulphide in crude oil and natural gas while they are still in the ground.

Even a one percent trace of sulphur turns oil into what's known as "sour crude", which is toxic and corrodes pipelines and transportation vessels, said James Tour from Rice University.

The cost of turning the sour into "sweet" crude is very high.

The nanoreporter developed by the scientists is based on nanometre-sized carbon material.

When exposed to hydrogen sulphide, the fluorescent properties of nanoparticles immediately change.

When pumped out of a production well, the particles can be analysed with a spectrometer to determine the level of contamination.

Modifying the particles with common polyvinyl alcohol (PVA) was the key to making the nanoreporters stable in temperatures as high as 100 degrees Celsius.

Testing in beds of sandstone or with actual Kuwaiti dolomite, to mimic oilfield environments, helped the team perfect the size and formula for nanoreporters that are most likely to survive a trip through the depths and return with data, said the study.

"The method of detection is so sensitive that large amounts of nanoreporters need not be pumped downhole," Tour said.

"This is enormously important for workers in the field to know for aspects of safety, lifetime of equipment and value of the afforded oil," he said.

Limited exposure to hydrogen sulphide causes sore throats, shortness of breath and dizziness, according to the researchers.

The study appeared in the journal ACS Applied Materials and Interfaces.