Seven years ago, the Deepwater Horizon oil well blew out, spilling an estimated 210 million gallons of oil into the Gulf of Mexico. Investigators found numerous mechanical and human errors, which led to the explosion at the concrete base of the rig. One of the possible failures included the foamed cement used to line the bore hole.
Shortly after the accident, researchers at the National Energy Technology Lab, or NETL, based in South Park, were mandated to become the leading experts in foamed cement.
“There was a lot that was assumed about its properties in a well,” said NETL Senior Research Scientist Barbara Kutchko. “Down in a well, you’ve got pressures, you’ve got temperatures, you’ve got very different environments than what’s up here at atmosphere.”
Foamed cement is used in about 90 percent of wells in the gulf. It’s basically concrete without any rocks or sand that has been laced with soap and injected with nitrogen, just like soda is infused with carbon dioxide.
Drillers change the ratios depending on what type of rock or soil has been cut by the drill.
“If the cement that they use is too heavy, it will fracture the formation and you’ll lose the cement.” Kutchko said. “If the cement isn’t heavy enough, then the opposite will happen. The fluids, the gases from the formation will enter into the cement before it’s set up. So you have to get that density just right.”
Think of the layers of earth like a cake. The foamed cement would consist of different formula for each layer, the spongy cake, gooey raspberry filling or creamy frosting. Depending on the pressure and density, the foamed cement might be formulated with larger or smaller bubbles.
Once the foamed cement cures it needs to be strong enough to keep everything in place long-term.
Kutchko said that means the bubbles need to be just right.
“You want them nice and small, you don’t want them touching each other,” she said. “The minute they start touching each other, they start forming up and coalescing then you get problems.”
The bubbles could form channels through which gas could migrate. The lines of bubbles could also form weak spots and maybe even fractures.
That’s why drillers make test batches of their foamed cement in their on-shore labs to try to find the right mix. But the change in pressure complicates that. At sea level, there is one atmosphere of pressure pushing on those nitrogen bubbles. But below the gulf, it could be 100 times that. It’s basically the opposite effect of opening a plastic bottle of soda in an airplane.
“Nobody has ever seen what these bubble look like generated under wellbore conditions,” Kutchko said.
But researchers can’t just go dig up a well casing and examine it, so Kutchko’s team worked with three energy companies to pump foamed cement into tubes at roughly 1,000 pounds per square inch.
Those 3-foot-long samples were allowed to cure before going through CT scans at the NETL Lab in Morgantown, W.V., while they were still under pressure.
“And what we’re finding is that (under) pressure, you get much smaller bubbles which is really good,” Kutchko said.
Researches mapped and measured each one of the roughly 170,000 bubbles per cubic centimeter found in the samples. Those samples were then taken out of the high-pressure casings and examined at the South Park lab for brittleness, flexibility and a long list of other properties.
“Instead of saying, ‘Oh well it’s always worked before, so we must be doing something right.’ Now you know exactly what you’re doing and why you’re doing (it) and how,” Kutchko said.
She said she would still like to examine the impact high temperatures have on the cement and how different flow rates could change its properties.
“Every bit of date that we’re producing in this lab, were putting it out as fast as we can and the service companies, the operators, they’re taking that data and they are using it to improve their models,” Kutchko said. “They’re using it to improve their designs. They’re using it to improves the cement itself.”
According to the EPA, storing carbon dioxide underground, in some cases in abandoned wells, could be a way to hedge against climate change. So, the lab is also looking at how contact with carbon dioxide would impact the foamed cement. Researchers are even looking at the possibility of using carbon dioxide instead of nitrogen to lock away the greenhouse gas today, rather than after a well has been drained.
Officials with the Marcellus Shale Coalition said they're not aware of any drillers in Pennsylvania using foamed cement.
In this week’s Tech Headlines:
- An annual report released by the industry group CompTIA found Pennsylvania's technology industry grew by 5,000 jobs last year, or about 2.2 percent. That puts the total number of tech jobs at nearly 240,000, which is the eight most of any state. However, when tech jobs are seen as a percentage of a state’s total workforce, Pennsylvania ranks 26th. The average tech job in Pittsburgh pays about $88,000 a year.
- Democratic Congressman Mike Doyle, of Swissvale, launched an online petition on Whitehouse.gov calling on President Trump to veto S.J. Res 34, which he said would negatively impact Internet privacy. The resolution would overturn the FCC’s recent regulations requiring Internet Service Providers to get a users’ consent before collecting and sharing sensitive personal data. No Democrats voted for the measure when it was passed in the House and Senate last month.