Carbon Intensity: A New Metric for Evaluating Energy
Methane emissions and carbon intensity from oil and gas production in the Gulf of Mexico (GoM) may be much higher than U.S. government estimates indicate, and also much higher than onshore emissions.
Carbon intensity (CI) – a metric for proportional emissions relative to units of energy – is defined as “grams of CO2e of greenhouse gas emissions per megajoule of energy produced.” CI can help companies, regions, and nations compare the relative climate impact of energy production.
Offshore Intensity: Deep vs Shallow Water
The relatively lower CI of GoM deep water production is primarily the result of combustion (flaring), while shallow water production facilities have much higher CI due to fugitive methane emissions (venting and leakage) from central gathering and processing infrastructure.
CI can be difficult to accurately evaluate, as emissions can be intermittent or persistent, and measurements of both CO2 and CH4 from offshore oil- and gas-focused operations are difficult to perform. The challenges of reaching remote locations and capturing emissions data safely are pushing organizations to implement remote sensing and data measurement technologies (drone-, plane- and satellite-based).
One recent study, based on U.S. Bureau of Ocean Energy Management (BOEM) data as well as new aerial data collected from about 8% of Gulf shallow water assets, calculates the CI of deep water production at 1.1g CO2e/MJ and the shallow water production CI between 16 and 43 g CO2e/MJ. Some of the observed shallow water central hubs, particularly those with older infrastructure, were categorized as super emitters.
Comparing Carbon: Onshore vs Offshore Production
As with onshore marginal wells, shallow water wells with low production correlate to proportionally higher emissions. High resolution imaging revealed that shallow water facility tanks, pipelines, and satellite wells were the primary sources of observed methane emissions. Methane loss rates from onshore operations (Permian basin) are estimated at about 3.3% to 3.7% while shallow water methane escape (loss) rates may be from 23% to 66% in the Gulf.
Shallow water operations are creating substantially more climate impact, which can be addressed through efficient flaring in place of venting, repairs of leaking equipment, and well plugging and sealing. As with onshore sites, understanding the volume and sources of the offshore emissions is still a work in progress.
Closer Look: Sources, Concerns, and Mitigation
The substantial shallow-water CI is likely the result of “cold venting” of excess gas, potentially as a result of non-optimal product volumes through the central handling facilities and/or leaks in aging transport and storage infrastructure. Some of these releases may be going undetected, and therefore not reported and included on federal or state databases.
An additional hazard of these large-volume methane emissions around GoM platforms is the risk of engine shutdown from methane intake in the helicopters transporting supplies or transferring personnel. This potential danger to flights is still being researched. More accurate measurements and indicators of methane releases could alert pilots and avert catastrophic engine failure.
Once persistent emissions sources are identified, targeted mitigation efforts can create rapid methane reductions, lowering the CI of energy production. Mitigation can include refurbishment or replacement of pipelines and storage tanks as well as plugging and sealing of marginal wells. As companies and governments look for ways to cost-effectively reduce methane emissions, lowering the CI of GoM production offers a rapid positive climate impact.
While BioSqueeze® has not yet been implemented in an offshore environment, it has proven to be the most effective solution for eliminating annular methane leaks and gas migration issues in onshore oil and gas wells. BioSqueeze Inc. is currently seeking partners for shallow water GoM offshore field trials to start in late 2024.
