Quantifying Methane from California’s Plugged and Abandoned Oil and Gas Wells
Several studies have examined methane emissions from abandoned oil and gas wells in the United States. California has more than 120,000 documented abandoned oil and gas wells, plus 30,000 idle and 70,000 active wells. To evaluate methane super-emitters in the state, NASA/JPL undertook an aerial survey of methane point sources. The survey included 88 percent of all documented California oil and gas wells and found that 107 wells were leaking methane above the threshold of detection (2 – 10 kilograms per hour). Complementing the aerial survey work, the project team for this study measured emissions from a sample of 121 wells using ground-based instruments. These instruments included a rapid and nonintrusive mobile plume integration instrument and highly sensitive static flux chambers. The measurements provided three to nine orders of magnitude greater sensitivity than the aerial measurements. The researchers adopted an upper limit “leak threshold” of 1 gram of methane per hour. The team measured 97 abandoned and plugged wells, finding only one that exceeded the leak threshold. The researchers also found leaks from 11 of 17 idle wells (mean emissions: 35.6 grams of methane per hour), 4 of 6 active wells (mean emissions: 189.7 grams of methane per hour), and 1 unplugged well (10.9 grams of methane per hour). Acknowledging the small sample size of wells not in the “abandoned and plugged” category, the project team suggests that idle and active wells may account for most emissions from all well status designations. Overall, the sample of wells in this project suggests little evidence for extensive leakage from plugged and abandoned wells in California. However, the researchers acknowledge the sample, obtained from small fields on public and private lands, may not represent most abandoned and plugged wells that are primarily located in active major oil and gas fields.