GE Global Research announced it has signed a contract with the National Energy Technology Laboratory (NETL), part of the US Department of Energy (DOE) national laboratory system, to build a multi-point sensing system to monitor carbon dioxide (CO2) injected into geothermal containment wells. The use of these cavities, which extend 1-2 km below the surface of the earth, is being explored by the federal government and power producers as an option for the long-term storage of CO2.

Carbon dioxide emitted from the combustion of fossil fuels has long been an environmental concern. It represents 84 per cent of US greenhouse gases, according to a 2010 analysis by the US Environmental Protection Agency. Carbon capture and sequestration of highly pressurised CO2 in underground wells is viewed as a promising alternative to the release of CO2 gas into the atmosphere.

Highly accurate monitoring, verification, and accounting are critically important to ensure that CO2 pumped underground is confined to the potentially porous or fractured rock that contains each well. Currently, GE is testing a fibre optic cable with a sensor that can measure temperature and pressure at a single point inside the well. Readings from that pressure sensor have been calibrated to an accuracy of ±0.1 per cent. This follow-up project would add a yet-to-be-determined number of additional sensors along the length of a multi-kilometre cable, enabling engineers to track the disbursement and movement of CO2 within the sequestration well with even greater precision.

“Our goal is to develop an incredibly resilient cable and sensor system that can withstand an extremely harsh environment for an extended period of time – temperatures as hot as 250° C and pressures topping 10,000 psi,“ said Dr William Challener, principal investigator and physicist in the Photonics Lab at GE Global Research. “The work is very challenging. We have already developed a single sensor system that can tolerate temperatures as high as 374° C and 3,000 psi for short periods. Now, we’ll leverage that knowledge to build a package that is even more robust and that can be multiplexed along the cable.”

CONDITIONS EXTREME
To illustrate how extreme these underground conditions are, Challener noted that 250° C is about 40 per cent hotter than boiling water and 10,000 psi is equivalent to the pressure encountered 4.25 miles under the ocean. Additionally, some high-power industrial power washers exert a pressure of 10,000 psi and those are capable of slicing metal and concrete.

Another key component of the project is wireless communication. GE scientists will develop a remote monitoring system capable of activating and operating the sensors from an off-site control room.

“The end-goal is to ensure confidence in the long term stability of CO2 sequestration sites,” said Challener. “We believe the fibre optic cable and sensing system we’re tasked with fabricating will help make that goal a reality.”

Work on the two-year, joint venture between GE Global Research and NETL is slated to get underway in January, 2013.

GE Global Research is the hub of technology development for all of GE’s businesses and operates from sites in Niskayuna, New York; San Ramon, California; Bangalore, India; Shanghai, China; Munich, Germany, and Rio de Janeiro, Brazil.