Methane Emissions from Leaking Idle Oil Wells

Carbon Mapper Data Dispatches are regular communications highlighting insights and information from the Carbon Mapper Data Portal. We believe transparency is critical in the global fight against climate change. That’s why Carbon Mapper is committed to delivering accessible data on methane and CO2 emissions so that it can be used by policymakers, regulators, operators, and civil society to guide science-based action to reduce emissions.

Data Highlight

What we See 

The images in Figure 1 are the result of Carbon Mapper analysis of data collected by overflights on May 20, 2022, with JPL’s next generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG). The false color image of the invisible plumes indicates the extent of methane above the detection limit of this instrument and is representative of other detections on the same date. Preliminary methane emission rate estimates for the combined source are in the range of 45-114 kilograms per hour. These estimates may be refined with subsequent analysis and uncertainty quantification. The plume origins are consistent with leaks at two idle oil wells (identifier numbers 04-029-08792 and 04-029-71724) reported by California Geologic Energy Management Division (CalGEM) based on site surveys conducted on May 21.

The methane plumes at these locations were not detected by our subsequent overflights on May 23 and May 30, likely as a result of the wells subsequently being plugged based on reports attributed to CalGEM.

The images provide quantitative information about the methane emissions from these leaks which translate to surface concentrations of the gas, and potential flammability hazard at various locations. Surface concentrations of methane gas depend on the emission rate, wind speed, direction, distance from the source, and potential for accumulation in enclosed spaces.

Deriving precise estimates of surface concentrations under all wind conditions can require complex computer modeling. However, in this case, our remote sensing observations provide some bounds on potential methane surface concentrations using nearby wind measurements and some assumptions about plume thickness at different distances for the emission sources. For example, our observations of methane concentration pathlengths are consistent with surface concentrations of around 50,000 parts per million (ppm) right at the leak assuming an initial methane plume thickness of about 5 centimeters. However, at a distance of 100 meters downwind from the leak, we would predict surface concentrations of about 10 ppm assuming a plume thickness of 10 meters (more likely lower if the plume spreads out in response to winds and diffusion). 

Why it Matters

This example highlights why sustained, wide area monitoring from high resolution methane sensing satellites is important to supplement periodic surface site surveys and continuous sensor networks to provide timely detection, quantification, and communication of high-emission methane events.

Assessing immediate local impacts of methane leaks

These observations provide a direct estimate of methane emission rates at the source of the leaks that can be used to provide a visual and quantitative assessment of gas concentrations and the flammability hazard in the surrounding areas. For reference, the lower explosive limit of pure methane in the atmosphere is 5% by volume (50,000 ppm). While not a substitute for surface sensors used by public agencies and first responders to detect the presence of high gas concentrations at a given location, remote sensing can provide additional quantitative information for those agencies and improve understanding by surrounding communities.

Understanding longer-term climate and air quality impacts

This data provides an initial snapshot of emission rates for the overflights conducted on May 20, 2022. Translating these to estimates of long-term total release of methane and potentially other co-emitted pollutants (not directly detectable with these measurements) is challenging given the lack of continuous methane monitoring in most areas and incomplete information on the composition of associated gas in oil fields.

Filling observation gaps efficiently and cost-effectively

There is currently a lack of direct monitoring for most idle and abandoned wells across most of the US, and additional observations are needed to accurately quantify the magnitude of methane emissions from this class of wells.

Figure 2 illustrates that this area was not surveyed by our California Methane Survey overflights between 2016 and 2021. While our previous overflights surveyed an estimated 88% of reported oil and gas infrastructure in California, those research studies were not designed to provide complete and continuous monitoring given the high costs and limited availability of aircraft with the necessary measurement performance. For example, that initial survey required several months of aircraft overflights spread over two years. In addition, conducting direct surface measurements of a larger selection of abandoned and idled wells in California is challenging logistically, particularly on private property, and could benefit from additional study.

Based on our preliminary emission rate estimates, these leaks and others in the future would be detectable by the Carbon Mapper satellites. This offers promise for future improvements in accurate accounting and mitigation of methane emissions to minimize global climate impacts as well as addressing health and air quality issues for local communities.