HARD SCIENCE: Research to better understand cement and how to control it could be put to good use, helping companies like BP and Halliburton design more reliable cements for sealing oil wells deep beneath the ocean and, hopefully, avoid catastrophes such as that which occurred in the Gulf this year. Image: COURTESY OF BART COENDERS, VIA ISTOCKPHOTO.COM
After months of hearings and finger-pointing, a Deepwater Horizon investigative commission formed by President Obama has begun to shed light on what led to the April 20 explosion that killed 11 and initiated a deep underwater gusher that spewed more than 750 million liters of crude into the Gulf of Mexico. Yet one of the biggest mysteries remains—why did the drillers use cement designed to shore up the well despite warnings that the mixture would not hold?
The National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling earlier this week concluded in their report (pdf) that there were clear indicators of problems with the cement mixture prior to the explosion. In particular, negative-pressure tests designed to determine whether the well casing could provide a barrier to the gas and oil failed, meaning there was a danger of hydrocarbons escaping up to the rig and catching fire, according to the seven-member, bipartisan commission, which President Obama appointed in May.
Judged through the lens of science, the commission's report is less a condemnation of well owner BP or cement contractor Halliburton than an indicator that, even though the binding agent has been in wide use since Roman times, the chemical properties of the material itself is still largely a mystery.
"It's pretty amazing that, given the importance of it, not a lot of scientific study has been done of cement," says Brad Chmelka, a chemical engineering professor at the University of California, Santa Barbara. "We're asking it to do things in extreme conditions that it wasn't designed to do and isn't optimized for."
Cement begins as a powdery mix of grains made by grinding and then heating limestone with small amounts of other materials such as clay. The addition of water to the powder initiates a chemical reaction that causes the grains to adhere to each other and form strong, stable bonds. For this reason, cement is used as the main binding agent in concrete, a building material that also includes sand, gravel and other granular substances. Certain formulations of cement, those used for deep sea drilling, for example, have the ability to harden and set even underwater.
The way cement is currently used in different industries is the result of a tremendous amount of accumulated wisdom, says Chmelka, who is part of a team that for several years has been studying the molecular properties of cements. That team includes researchers from the University of California, Santa Barbara, Princeton University, Imperial College London, Roberts Consulting Group in Acton, Mass., RTI International in Research Triangle Park, N.C., and Halliburton, which has provided much of the project's funding. Halliburton's ongoing role in the research has been to inform the researchers on the conditions that matter when formulating and working with cement, such as realistic temperatures and cement compositions, Chmelka adds.