Cement's properties depend strongly on the mix's molecular-level composition and its reactions with water to form a hydrated solid. The strength of the cement develops with hydration reactions that promote molecular cross-linking, Chmelka says. "Given the complexity of the mixture, we thought it would be an unresolvable distribution of components that we couldn't identify, but that's not the case," he adds. The research team reported in its first study, published in May in the Journal of the American Chemical Society (JACS), its use of solid-state nuclear magnetic resonance (NMR) spectroscopy to distinguish among different molecular rearrangements that occur as a result of cement hydration and setting.
Still, the molecular compositions, structures and changes that occur as a result of hydration are poorly understood, because cement has a composition that is partially crystalline, partially disordered, and holds multiple components that also change with time, Chmelka says.
Chmelka and his colleagues are trying to gain an understanding of cement at the molecular level to determine properties such as how calcium and magnesium ions are affected by and participate in the hydration process as well as how cement setting can be slowed or better controlled. For their next paper the researchers are specifically studying retardants—how they inhibit solidification and how sugars bind to and affect the different components used to make cement, Chmelka says.
The results of this research could be put to good use, helping companies like BP and Halliburton better design a reliable cement for sealing oil wells deep beneath the ocean and, hopefully, avoid catastrophes such as occurred in the Gulf this year. Cement used at underwater drilling sites is designed to flow down the center of a well bore so that it does not set on the way down. In the case of the Deepwater Horizon, Halliburton added nitrogen gas to the mix to improve the cement's ability to flow. Once at the bottom, the cement needed to overcome pressure from the well bore and flow up the annulus (the space between the casing and the sides of the bore hole), where it should have set and blocked any oil or gas from escaping.
The commission obtained samples from Halliburton of the cement recipe used on the failed well, including the same proportion of nitrogen gas used as a leavening agent, along with a number of chemicals used to stabilize the mixture, according to an October 28 letter (pdf) from Fred Bartlit, the commission's lead investigator. The foamy cement mixture was sent to a laboratory owned by BP-rival Chevron for independent testing. Chevron conducted a series of postmortem tests and reported being unable to generate stable foam cement (one that would set properly in the annulus) in the laboratory using the materials specified by Halliburton and available design information regarding the cement used at the Macondo well, according to the commission. Chevron conducted nine separate stability tests intended to reproduce conditions at the BP well, and the cement failed them all.
Halliburton defended itself by pointing out that "significant differences" between its internal cement tests and the commission's test results may be due to differences in the cement materials tested, according to a statement posted on the company's Web site. The commission's tests were not an apples-to-apples comparison because they used off-the-shelf cement and additives, whereas Halliburton tested the unique blend of cement and additives that existed on the rig at the time the latter's tests were conducted, the company claims.
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7 Comments
Add CommentThe problems Halliburton had with their cement in Iraq should have given you a clue in how they do business and you should had stayed away from them.
Reply | Report Abuse | Link to thisDon't you have to burn the limestone instead of just heating it up a little bit? How is cement going to hold under water if you put all those chemicals in it to keep it fluid? Isn't it obvious now that the chemicals and minerals in the seawater reacted against those chemicals and developed a problem?
Didn't Chevron conduct their tests according to the specifications of Halliburton. It is going to be a bit difficult for Halliburton to lie their way out of this one and place the blame on Chevron's store bought cement.
I was told that the secret of the roman's cement was lost, as well as the way they produced the red pottery "terracota". Is this still true ?
Reply | Report Abuse | Link to thisFor all the obvious potential of this research, it's worth noting one thing. All the science in world won't help if well operators can ignore findings they don't like, and get away with it. We'll have more blowouts until the culture changes.
Reply | Report Abuse | Link to thisI doubt that the well operators(those on the rig)will knowingly endanger themselves by using unsafe materials or practices .
Reply | Report Abuse | Link to thisThe men on the rigs are skilled intelligent and to suggest that stupid like alflanagan is being dim.
Sounds like we have a smoking gun to me... Haliburton may have been paid to sabotage the well and create a disaster, or a diversion.
Reply | Report Abuse | Link to thisTo clarify a misquote attributed to me in the 4th paragraph of the article:
Reply | Report Abuse | Link to thisThere has of course been a great deal of scientific study conducted on cement chemistry and properties; this is evident in a number of scientific journals that focus on the science, research/development, and/or technologies of cement, including for example the Journal of Cement and Concrete Research.
The quote in the first sentence of the 4th paragraph should have properly stated:
"It's pretty amazing that, given the importance of it, much still remains unknown at a molecular level, which current research seeks to address."
A great deal remains still to be learned, especially at a molecular level and under the harsher and more specialized conditions associated with increasingly diverse applications, including for deepwater oilwells.
Roman cement was a mix of volcanic ash and hydrated lime. Very slow set time but very strong. When heating limestone, the CO2 is “burned off” and you have lime (quicklime). It must be hydrated to work as cement. Lime cement is not hydraulic (it will not set under water). The volcanic ash mixed with the hydrated lime made a pozzolin, i.e., a material, with calcium hydroxide that will set under water. Its name comes from Pozzuoli, Italy where it was first used by the Romans.
Reply | Report Abuse | Link to thisPortland cement is made from limestone and clay and needs a much hotter oven to make.