Diamondoids: A Driller’s Best Friend
Diamonds may be a girl’s best friend, but diamondoids are a driller’s best friend, especially when it comes to exploration and production of unconventional gas. So said Jeremy Dahl, Research Associate at Stanford University Department of Advanced Materials, who spoke at the Tight and Shale Gas Summit in Budapest, Hungary.
Diamondoids are in fact extremely small diamonds, about a nanometer in size. He showed a photo image of a smiling female. “She’s happy because I’ve given her a spoonful of diamonds.” he quipped, explaining: “Because of their stable diamond structure they are the ultimate oilfield nano sensor.”
“As explorers we want to be in the right part of the shale,” he explained. “In the US you want to be where the liquids are. We’re going to talk about how you determine what part of the shale you want be in and which areas to avoid.”
Mr. Dahl said that via “nano diamonds,” he and his colleague Professor Mike Moldowan of Stanford University’s School of Earth Sciences had developed a method to map out the distribution of dry gas versus gas and light oil versus heavier liquids in tight shales. The method can also be used to calculate maximum pressures generated through oil cracking.
He explained that to evaluate a shale play one had to map out rock and organic matter properties, like natural fracturing.
“You want to understand your shale so you know where to go.”
Dahl mentioned INGRAIN Digital Rock Physics Lab, a company that can measure porosity on the nano scale.
“They are the experts on organic matter,” he commented. “What you want to look at is first of all is the total organic carbon, make a map of it, then look at the generation potential of the organic matter. Then you want to determine how much gas and oil have already been generated from the kerogen. Then you want to look at how much of the oil has been cracked to gas.”
Regarding thermal maturity, he questioned “how much of the oil and gas has already been generated?”
He listed methods and said that basically the object was to map out this thermal maturity.
“For mapping out oil cracking, we’ve developed a method based on diamondoids. Admantane, the simplest diamondoid, is present in every petroleum in the world,” he said.
He showed the delegates some other naonmaterials.
“Take your oil shale,” said Dahl. “It contains liquids and if we heat it up enough, if you get above that activation energy they crack down to methane and graphite.”
He contrasted, “Diamondoids are not going to crack - mother nature’s internal standard to monitoring this reaction here.”
Then, he showed an area of Mexico where there was heavier oil, dry gas and light oils and condensates.
“You’re converting a liquid to a gas, so we have to make quite a few assumptions and you can get some idea of how much natural pressure is being generated,” he said, explaining that different diamondoids could be used to determine a source.
“Get as many maps as you can, because you’ll be way ahead of the game,” continued Dahl. “You’ll be able to map out the distribution of dry gas versus gas and light oil versus heavier liquids in tight shales.”
His colleague Mike Moldowan added more insights.
“Parts of tight shale can act more like conventional reservoirs,” he said. “We see this very strongly in studies we’ve done in the Williston basin.”
According to Moldowan, it was a matter of pinning down fluid sources and unravelling mixtures.
“It’s important to note that the diamondoids survive the oil cracking process. The original diamondoids can give you the original source. You can use the diamondoids as a fingerprinting method,” he explained.
Moldowan said the Williston was a complex basin with as many as 12 proven sources. “If you know that you’re in one prospect and see oil or gas from another prospect then you know you can go deeper.”
In addition to the cracking, which was important for tight shale analysis, he said this could be an added feature for knowing what was mixing, i.e. what the sources were.