Gathering and Processing Frequently Asked Questions
Who sponsored the study?
The Colorado State University-led gathering and processing study is sponsored by the Environmental Defense Fund and five energy companies, four of which have substantial operations in the gathering and processing segment of the natural gas industry. It is one of 16 studies organized by EDF and industry partners to quantify methane emissions across the country’s entire natural gas supply chain.
How many sites did the team visit?
The CSU-led research team, which also included researchers from Carnegie Mellon University and Aerodyne Research, measured methane emissions at 114 gathering facilities and 16 processing plants across 20 natural gas basins in 13 states. It is believed to be the first large-scale study to measure emissions at gathering facilities and the largest to date on the gathering and processing sectors.
How were the sites selected?
Partner companies provided the research team with a list of all of their gathering facilities and processing plants. Industry partners also provided site access and detailed facility data (natural gas throughput, gas type, gas composition, equipment inventories, compressor power, age, and inlet/outlet pressures.) The gathering facilities sampled were selected at random from the combined partner inventory of greater than 700 facilities. The 16 processing plants sampled represented all accessible partner processing plants. The origin of the gas entering the gathering facilities and processing plants included shale gas, coal bed methane, conventional gas and tight gas.
Can you tell me the location of the sites that were selected and which company operates each one?
That information is not publicly available. The partner companies involved in the study provided the research team with access to sites on the condition those locations not be made public.
How were measurements taken?
The research team used two independent, yet complementary, measurement techniques to quantify the methane emissions at each of the sites – infrared gas imaging and downwind dual-tracer flux. The methods were performed simultaneously so researchers could compare the quantitative results from the dual-tracer flux to the qualitative results from the infrared imaging, which indicated the major sources of leakage at each facility.
Why use two sampling methods?
The downwind dual-tracer flux method accurately captures the total emissions from each facility but does not pinpoint the source. The infrared imaging can pinpoint the source of a major methane leaks but it does not produce a quantitative measurement. The two measurements are complementary.
When were the measurements taken?
Measurements were taken between October 2013 and April 2014.
What is infrared gas imaging?
With this method, leak sources are identified using real-time infrared imaging.
What is downwind dual-tracer flux measurement?
Research personnel released specific “tracer gases” (acetylene and nitrous oxide) at carefully controlled rates from each facility. A second group of research personnel measured concentrations of the tracer gases, along with methane, ethane, carbon dioxide and other gases downwind of the site using high-time resolution instruments mounted in a mobile laboratory. Measurements of the tracer gases are correlated with the measurements of methane to estimate the amount of methane being emitted at the facility. Measurements of other gases, such as ethane, allow the researchers to distinguish between methane emitted from the facility versus methane emissions originated from other nearby sources. This method is used to measure the magnitude of overall methane emission for a facility.
How many samples were taken at each site?
The amount of data collected at a facility varied by the type and size of the facility, accessibility and other conditions. Multiple tracer gas plumes (10 to 100) were acquired from each facility and only those facilities where a sufficient number of plumes (>3 and typically 10 to 20) that passed the method’s quality control criteria were included in the final 130 facility dataset.
Are raw data publicly available?
Yes, raw and interpreted data from the onsite measurements and analyzed data from the tracer flux measurements will be made available on this website under the "Research Results" section upon publication of each manuscript.
Will the study team publish other papers on methane emission in the gathering and processing sectors of the natural gas supply chain? If so, when?
The study team has published three papers to date. The first paper focuses on the measurement methods and was published in Atmospheric Measurement Techniques on May 7, 2015. The second paper focuses on the experimental results from the field campaign and was published in the journal of Environmental Science and Technology on February 10, 2015.
A third paper published to date focuses on developing a national estimate of total methane emissions from gathering and processing and was published in Environmental Science and Technology on August 18, 2015.