According to the U.S. Environmental Protection Agency’s (EPA) “Inventory of U.S. Greenhouse Gas Emissions and Sinks,” methane accounts for about 10% of U.S. greenhouse-gas (GHG) emissions. Of this, one-quarter is from the natural gas industry.
Expressed as a percent of natural gas production, this equates to 1.3% of production. While other studies have suggested much higher emissions levels, some as high as 7.9%, the most recent and most comprehensive non-EPA study—a multiyear study organized by the Environmental Defense Fund and involving various universities and research organizations—found emissions only slightly higher at 1.7%. The paper tabulates emissions for both crude oil and natural gas systems at 2.3% of gas production. Consulting service ICF International estimates that the natural gas portion equates to 1.7% of emissions.
ICF has been a leader in measurement and mitigation of methane emissions from the oil and gas industries for more than 20 years. This has included work for the industry, regulators and nongovernmental organizations ranging from policy analysis and development to direct support for industry operations.
Over the last five to 10 years, the company has seen increasing focus on methane emissions from these industries for several reasons. Among those is that the climate-forcing effect of methane is greater than that of CO2. The global warming potential (GWP) describes the ratio of methane equivalent to 1 ton of CO2 and can range from 34 to 86, depending on the timescale being considered.
On the positive side, this means that reducing 1 ton of methane is equivalent to reducing 34 to 86 tons of CO2. In addition, there are available methane reduction technologies for most of the emission sources.
When methane emissions can be captured and sold, the value of the gas offsets the cost of the reduction measure. In some cases, the value can be greater than the cost. That said, the value cannot always be directly monetized by the operator due to regulated pricing structures (e.g., for pipelines and distribution companies).
On the other hand, reducing methane emissions is complicated by the fact that the natural gas industry is actually several different industries with different types of emission sources and ownership and regulatory structures.
The EPA inventory includes more than 100 different industry segment/emission source categories. The nearby graphic shows the EPA estimate of emissions in the various industry segments. Gathering and boosting is the largest, followed closely by development and production, and then transmission and storage.
Methane emissions from oil and gas operations have declined significantly since the EPA started tracking them, decreasing from almost 200 million tons of CO2 equivalent (MMtonCO2e) in 1990 to 164 MMtonCO2e in 2016.
According to the EPA, the unit CO2e represents an amount of greenhouse gas emission whose atmospheric impact has been standardized to that of one unit mass of CO2, based on the global warming potential of the gas.
Moreover, natural gas production has increased significantly during that same period, so emissions per unit of production have been declining continuously, falling by 45% from 9 kilograms CO2e/Mcf in 1990 to 5 kilograms CO2e/Mcf in 2016.
There are several reasons for this continuing decline.
As equipment is replaced and new equipment comes online, the new equipment is typically cleaner and more efficient. The industry has also made significant voluntary reductions, including those made in cooperation with the EPA Natural Gas STAR program, which has reported more than 28 billion cubic meters(equivalent to 1 trillion cubic feet) of methane reductions.
In recent years federal regulation (e.g., New Source Performance Standards) and state regulation (e.g., Colorado Reg 7 and Pennsylvania GP-5) also have resulted in reductions. Nevertheless, there are still opportunities for further reductions.
In 2014, ICF completed a study that quantified the opportunities and costs for methane reductions in the natural gas industries. Since then, the quantification of baseline emissions technologies has improved, new regulations have changed the baseline, mitigation technology costs have declined and new technologies have been developed. Although the specific results of the study could bear updating, they are useful for an initial survey of current opportunities for reductions.
Some of the opportunities, while still cost-effective, are no longer as large because they have now been implemented at many facilities or are now required by regulation. For example:
- Emissions from well completions for hydraulic fracturing are regulated to a high degree of reduction;
- Many high-bleed pneumatic devices have been replaced and low-bleed pneumatics are now required for many applications;
- Instrument air is required in certain applications as a replacement for gas-powered equipment;
- Scheduled rod packing replacement is now required for reciprocating compressors in some applications; and
- Wet-seal compressor emissions are lower than previously thought.
Although many of these opportunities might be smaller than projected a few years ago, some of them still might be attractive. In addition, other opportunities that have changed less present good possibilities.
One is leak detection and repair programs and control of nonstandard emission events. Structured periodic inspection and leak detection programs are important to maintaining good equipment performance, identifying equipment problems that create emissions and avoiding intermittent malfunctions that can result in large emissions.
Another such opportunity might be better control of liquids unloading. Well venting to control liquids is a potentially large source of emissions. There are a variety of alternative measures depending on the age and other characteristics of a well, so there is no one solution, but lower emitting solutions exist and should be pursued. New approaches might be required for horizontal wells as they age.
A third opportunity could be replacement of pneumatic pumps. Electric pumps or instrument air can be highly cost-effective alternatives where electricity is available, either from the grid or onsite gas- or solar-powered generators.
Vapor recovery from tanks is still an important option even though more tanks have been regulated in recent years.
Finally, flaring of stranded gas from oil wells could be an opportunity for implementation. Even as flaring is being reduced via improved infrastructure and due to regulation, there are still opportunities to reduce flaring through onsite gas use and/or capturing the gas via compressed natural gas methods or LNG.
Although the emissions are small in the overall inventory, reduction of methane from the natural gas industries can be a cost-effective option. While much progress has been made and is continuing to be made in GHG sustainability strategies, there are additional cost-effective opportunities to pursue.
Joel Bluestein is a senior vice president of ICF International
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