Researchers have developed a new laser-based system that can pinpoint exactly where tiny methane leaks are over a surface area of several square miles. This system could be used to monitor methane leaks at oil and gas production sites.

This optical head holds the laser launching system that launches laser light out to retroreflectors located 1 kilometer away. It is shown operating during a test conducted at the Table Mountain Test Facility in Colorado. (Source: Sean Coburn, University of Colorado in Boulder)

Often methane gas leaks develop during gas and oil production or unknown leaks occur in production infrastructure. These leaks can be costly and dangerous for the people working on the machinery. Methane leaks contribute to climate change as well. The current method to find a methane leak is long and tedious. A team of workers has to travel to a site and use a special camera that is specifically sensitive to methane to check for a leak.

"Our approach allows measurements to be autonomous, which enables continuous monitoring of an area," said the co-lead author of the study Sean Coburn, from the University of Colorado in Boulder. "This technology could play a significant role in reducing methane emissions from production activities, easing tension between urban development and oil and gas production and helping avoid disasters like the 2015 Aliso Canyon methane storage leak that released 90,000 metric tons of methane into the atmosphere."

The new system detects slow and low volume methane leaks from almost a kilometer away. The team demonstrated this system to detect leaks with a flow rate equal to 25 percent of a person’s breathing rate. This method could be used to measure other gases as well and it is believed that the system could be helpful in air pollution research.

"Our system is based on frequency comb laser spectroscopy, which stemmed from the Nobel-prize winning work of Jan Hall at the University of Colorado," said Coburn. "Because of recent advances, we were able to take this technology out of the lab and use it in the field for the first time. Combining this precision spectroscopy technique with new computational methods allowed us to pinpoint methane sources and determine emission rates with unparalleled sensitivity and range."

Methane absorbs light at a specific infrared wavelength. This creates an absorption spectrum, like a fingerprint, which is used to detect gas. The new system uses a scanning laser beam that has discrete reflectors placed on the field. These reflectors determine how much methane is in the air which is intersecting the beam’s path. By comparing measurements from two laser beam paths, the system detects if a leak is present. It determines the location and size of the leak with new methods that take advantage of atmospheric models. These models simulate how the gas moves across the field.

The frequency comb laser is the key to this machine's operation. It emits hundreds of thousands of infrared wavelengths, as opposed to the one wavelength that traditional lasers emit. This kind of laser spectroscopy allows the system to gather measurements quickly over many wavelengths. This was important to the system because this is what distinguishes methane from other gases.

"The change in methane concentration downwind from a small leak is about the same as the change in methane due to dilution by water vapor that occurs when a rainstorm starts," explained Gregory Rieker, principal investigator on the methane sensing technology development project. "Laser frequency comb spectroscopy allows us to simultaneously, and accurately, measure water vapor and methane. This lets us correct for water in the air, which is critical for detecting very small increases in methane over a large area."

The system also has the ability to calculate background methane concentration, like changes in wind shifts, which is a major part of distinguishing a small leak from a larger, dangerous leak.

"A large proportion of the methane emissions that contribute to greenhouse gas emissions from oil and gas are thought to be from intermittent leaks," said Caroline Alden, co-lead author on the study. "To detect and analyze these types of leaks continuously, we developed computational methods that provide a history of how emissions vary over time."

The system was tested a few times. In these tests, the team mimicked scenarios that may happen in an oil or gas field. The team placed the frequency comb laser in a mobile trailer and then generated multiple beam paths that attempted to detect the gas leaks. The paths covered a kilometer of area.

In one experiment the system was configured to quantify small controlled leaks from around 50 meters from the laser beams. This showed that the system could determine when the leak was active, how emission rates changed in 20 hours even with emissions as low as 2 grams per minute.

In a different test, five methane leaks from different locations between laser beam paths were released for the system to attempt to detect. The system could pinpoint which sources were leaking as well as finding what the emission rates of the leaks are.

The team aims to refine the system by testing it in different scenarios. They also plan on working with industry partners to find if the system can work in actual oil and gas production sites. They are working with Longpath Technologies to commercialize the tech as a detection service.

The paper on this research was published in Optica.