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Lesson in the leaves
A deep understanding of materials science makes it possible to design molecules — and coatings for the oil and gas industry — that perform in desired ways.
Molecular science opens a host of possibilities for improving tool performance using specialised coatings and materials. Well-designed coatings can extend equipment life or improve a tool’s effectiveness. And it begins with modelling at the molecular level, says Sven Krueger, chief scientist at Baker Hughes.
“We do a lot of modelling at the molecular and atomic levels to really understand the physics and the behaviour of molecules at that level, and from there build the materials that we need,” Krueger says.
For example, it is possible to make a molecule that would normally attract water hydrophobic, or water repellent.
Hydrophobic surfaces are common in nature — scientists sometimes refer to the “lotus effect”, after the lotus leaf, which is covered with nanostructures that cause water to bead up and roll off. As an added benefit, the droplets pick up dirt and other contaminants, making the plant essentially self-cleaning.
Researchers are replicating that hydrophobic behaviour in the lab. “It’s a principle that we know from Mother Nature. If you look to the lotus leaves, they have a hydrophobic behaviour,” Krueger says, noting that hydrophobic coatings are sometimes referred to as lotus coatings.
“The real challenge is how do you make this work in the downhole environment. The potential is there for us to avoid operational problems, increase the reliability or extend the lifetime of a downhole tool. We can take it much further,” he says.
“Downhole conditions means high temperatures. Our temperatures in standard wells go up to 200 degrees Celsius and beyond. It’s high pressure, up to 30,000 psi.”
"We can change material properties that we could not change before."
Additionally, hydrophobic coatings need to survive corrosive, erosive and abrasive environments.
“We can almost make every material hydrophobic. We can change material properties that we could not change before,” Krueger says.
To ensure the engineered coatings meet operator requirements, the service company tests its hydrophobic coatings in downhole conditions at Baker Hughes’ Technology Center in The Woodlands, Texas.
One place where the right coating makes a difference is on the drillbit. For example, using a PDC bit with water-based mud in shale zones means there is a tendency for the cuttings to become sticky, which can lead to balling and plugging in the nozzles.
The cuttings build up and can slow the rate of penetration significantly, requiring the drillstring to be pulled to clean or replace the drillbit.
There are different ways to attack this problem, such as dosing the drilling fluid with certain additives, using electrical charges at the drillbit — which is more experimental at this point — or changing the surface property of the drillbit using a hydrophobic coating, Krueger says.
In 2016, Baker Hughes applied a hydrophobic coating to an 8 ½-inch drillbit that was used to drill a 1400-foot-long section, including a 400-foot shale section, in the Gulf of Mexico.
“You would have expected some bit balling issues. In our case, there was almost no difference in the drilling behaviour, which means the coating performed very well. When we pulled out of the hole, the drillbit was almost clean.
There were no shale cuttings that were sticking to the drillbit,” he says, adding the client was “happy with the success.” Most of the coating, he says, was still intact, meaning it resisted erosion and abrasion. He believes such anti-balling coatings will be used more often for drillbits.
On the completions side, a hydrophobic coating with anti-scale properties has been applied to a downhole safety valve, which can be used in the case of an emergency to close a well from the surface.
However, in certain locations, particularly in the North Sea and Canada, the subsurface safety valves are prone to scaling from carbonate and sulfate deposits in the production environment, which can compromise the valve’s functionality.
When such a problem is detected, it requires a workover to clean it. But coating the valves can prevent the build-up and can ensure a valve that is “functional for years,” Krueger says. “It extends the interval that you need to do the cleaning operation.”
Host of possibilities
Such engineered coatings could be applied across the industry, from drilling and wireline tools and permanent installations to surface installations.
“We can think of additional possible applications,” Krueger says. “We could imagine that we coat surfaces that we find in the subsurface environment.”
The vision is ambitious — to coat the rocks downhole to modify the reservoir’s wettability and thereby increase the recovery rate. “We would bring certain fluids downhole, inject them, coat the sand, with the ultimate goal to make it easier to recover the hydrocarbons that are in the formation,” he says. “That is a very cool idea, a very ambitious idea, but it is not impossible.”