A new surface coating developed by researchers with the Massachusetts Institute of Technology (MIT) (Cambridge, Massachusetts) causes water to bead on the inner surface of a pipe rather than spreading out. This prevents the buildup of hydrate ices that slow or block oil and gas flow and lead to a clog in an oil pipeline or well, which can cause expensive shutdowns to clear a pipe, or worse, a pipeline rupture from a pressure buildup.
When the Deepwater Horizon oil rig suffered a catastrophic explosion and blowout on April 21, 2010, the well’s operators thought they would be able to block the leak within a few weeks. On May 9, they succeeded in lowering a 125-ton containment dome over the broken wellhead. If that measure had worked, it would have funneled the leaking oil into a pipe that carried it to a tanker ship above. So why didn’t the containment dome work?
According to MIT, the culprit was an icy mixture of frozen water and methane, called methane clathrate (4CH4·23H2O). Because of the low temperatures and high pressure near the seafloor, the slushy mix accumulated inside the containment dome and clogged the outlet pipe, which prevented it from redirecting the flow. If it hadn’t been for the 4CH4·23H2O, the containment might have worked.
The new coating prevents clogs by promoting a water-barrier layer along the pipe’s inner surface. The coated surface attracts liquid hydrocarbons that are already present in the flowing petroleum, and creates a thin surface layer that naturally repels water. This barrier layer, the team found, can effectively prevent the adhesion of any ice particles or water droplets to the wall, which impedes the buildup of clathrates that could slow or block the flow. Unlike other methods that can be expensive or potentially polluting, such as heating of the pipe walls, depressurization, or using chemical additives, the new coating method is completely passive. Once in place, it requires no additional energy or material.
Critical to preventing these icy buildups is stopping the very first particles of clathrate from adhering to the pipe. Once they attach, they attract other particles of clathrate, and the buildup takes off rapidly, the researchers say. Their goal was to determine how to minimize the initial adhesion on the pipe walls.
“If the oil [in the pipeline] is made to spread more readily on the surface, then it forms a barrier film between the water and the wall,” explains Kripa Varanasi, MIT associate professor of mechanical engineering. In lab tests, which used a proxy chemical for the methane because the actual methane clathrates form under high-pressure conditions that are hard to reproduce in the lab, the system performed very effectively. “We didn’t see any hydrates adhering to the substrates,” Varanasi says.
The coating is described in the March 10, 2017 issue of ACS Applied Materials and Interfaces article, “Designing Ultra-Low Hydrate Adhesion Surfaces by Interfacial Spreading of Water-Immiscible Barrier Films,” by K. Varanasi, et al. The research was funded by the Italian energy company Eni S.p.A. through the MIT Energy Initiative.
For more information, visit news.mit.edu.