Quantification of Methane from California's Plugged & Abandoned Gas Wells: Effects of Land Subsidence and Other Factors
Improving our understanding of methane eimssions from abandoned and plugged oil and gas wells in California
Regents of the University of California, Davis
Recipient
Davis, CA
Recipient Location
3rd
Senate District
4th
Assembly District
$409,146
Amount Spent
Completed
Project Status
Project Result
The team measured emissions at 97abandoned and plugged gas wells and 24 wells that were either not properly retired (n=1), idle (n-17), or active (n-6). As documented in the final report (published August 2020), only one abandoned and plugged well was found to be leakingabove the research team's highly sensitive detection threshold of 1 g/hr. In contrast, the majority of the other (unplugged, idle, or active) wells were associated with leaks above the detection threshold. These results suggest that idle and active wells may account for mostemissions from all well status designations.
The Issue
Gas leakage from abandoned oil and gas wells is a concern because the primary component of natural gas is methane, a potent greenhouse gas. Previous work found that abandoned wells in Pennsylvania emit substantial amounts of methane, accounting for 5 to 8% of Pennsylvania's methane emissions from human activity. Regular monitoring of oil and gas wells is only mandatory during the active lifetime of the well. Because California has around 120,000 abandoned and plugged wells, there is an interest in quantifying methane emissions from those wells.
Project Innovation
This project measured emissions from a sample of 121 wells using ground-based instruments. These highly sensitive instruments provided three to nine orders of magnitude greater sensitivity than a prior survey by NASA/JPL that used aerial measurements to detect super-emitters from various sectors across the state. This project team measured emissions at 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.
Project Benefits
This work provides results on methane emissions from an initial sampling of abandoned and plugged wells in California that suggests emissions are small compared to other oil and gas methane sources and even smaller compared to other sources such as agriculture. These results indicate that current practices for abandoning wells may be adequate with no need for modifications whose costs could be borne by ratepayers. However, given the small sample size and without samples from major oil and gas fields, additional inquiry may be merited.
Affordability
These results indicate that current practices for abandoning wells may be adequate with no need for modifications whose costs could be borne by ratepayers. However, given the small sample size and without samples from major oil and gas fields, additional inquiry may be merited.
Safety
This agreement provided information to CalGEM (formerly Division of Oil, Gas, and Geothermal Resources) to prioritize technical review and maintenance of abandoned natural gas wells in the areas where land subsidence has occurred. The agreement also provided additional data to suggest that abandoned and plugged gas wells are not a substantial source of methane emissions in California.
Key Project Members
Marc Fischer
Subrecipients
Lawrence Berkeley National Laboratory
The Leland Stanford Junior University
