In 2016, regulatory authorities in North America started taking seriously the fact that methane is a very powerful greenhouse gas in its raw, or unburnt, form. They also took note that recent advances in thermal imaging technology had lent credence to the assertion that fugitive emissions, or unintentional gas leaks, are happening on a much greater scale than ever before.
Combined with an unprecedented expansion in U.S. onshore extraction and processing of natural gas, a basis for a perfect storm exists. An estimated $2 billion of natural gas is lost each year to leaks.
The idea of natural gas as a clean fuel that can contribute to a reduction in urban pollution and greenhouse gas emissions is well-accepted both within the oil & gas industry and beyond. Even the most prominent voices advocating for non-fossil-fuel renewable technology, including Greenpeace, publicly have accepted the important role natural gas plays in acting as a clean fuel stepping stone from energy based on coal or oil toward energy less reliant on fossil fuels.
This strategy of expanded exploitation of natural gas is working, and globally so. For example, on April 21, 2017 the UK enjoyed its first 24 hour power generation period completely free of coal since the year 1880. In the U.S., natural gas has surpassed coal as the nation’s leading power generating fuel source, with its growth rate surpassing any other energy source for power generation.
Reasons for uncertainty
Climate change commitments have been made by many western, economically developed countries. Gas is a key weapon in the fight against CO2 emissions. In Asia, growing unease about air quality in post-industrial China has led to some impressive deals with natural gas supply countries such as Russia and Australia, but it is also this very supply chain that sometimes calls into question the greenhouse gas reducing credentials of natural gas and its categorization as a clean fuel.
In the U.S., awareness of the raw methane emissions environment in the natural gas production and supply value chains has been growing. Emissions traces seen from space mirror the concentrations of activity around unconventional oil & gas production.
Raw methane is 86 times more potent as a greenhouse gas than CO2 when impact is considered over a 20-year period.
Methane is a powerful greenhouse gas in its unburnt form. Ultimately experts agree that if natural gas is to rival coal as a means of reducing greenhouse gas emissions, then emissions of raw methane in the supply chain must be held to less than 1% of total production.
In the U.S., raw methane emissions estimates have been ranging from a lower level estimate of 2% of overall production to around 17%. Alarmingly, the U.S. Environmental Protection Agency (EPA) in recent years has increased its estimate of emissions in upstream gas operations by 134%, bringing the overall total to 1.4% of total production (which from time to time they flag as a possible underestimation), or 40% higher than the target that must be met for gas to provide comparative advantage over coal.
Methods of measurement
But why do these estimates vary so widely? To answer this question, it is essential to also examine the "method of measurement" itself, and there are several different methods used.
One method to estimate leak emissions rates from equipment items having the potential to leak in any plant environment is simply to apply emissions factors and schedules provided by regulators. The emissions-per-equipment item then can be aggregated to a plant total to produce a volume for undesirable leaks, or fugitive emissions. This method takes no account of the actual leak rates, or if in fact the equipment is leaking at all.
The second, so-called incumbent, method is what is referred to as EPA Method 21. A measurement instrument, i.e., a flame ionization detector, is held near the stream of a suspected leak and measures the concentration of the fugitive gas in the atmosphere (typically on a parts-per-million basis).
It is difficult to underestimate the impact of Method 21-type emissions measurements on the oil & gas industry in recent decades. This method verifies that there is in fact a leak — vital information that can be passed on to repair programs. In this way, significant greenhouse gas reductions have been possible over the years, not to mention the valuable gas retained in the supply chain for end use.
However, the historic success of Method 21 testing still does not explain the wide variances in estimates for fugitive greenhouse gas emissions, nor adequately explain why, if the method is as effective as supposed, a methane emissions footprint is visible from satellites to an extent that alerts regulators to a growing problem. These questions themselves illustrate our increasing sophistication, in terms of technology and otherwise, in informing ourselves as to the nature of fugitive gas emissions.
Seeing is believing
One technology — which the EPA refers to as optical-gas imaging (OGI) — recently has been added to the list of regulator-allowable methods of measurement. It is essentially an infrared (IR) sensor capable of operating within the thermal spectrum. It generates an image of a gas leak that can be seen with the human eye.
For the first time, users see what a gas concentration reading from a Method 21 test never could allow them to see: a gas cloud.
Millions of TV-news viewers were introduced to OGI when they saw EPA footage of the Aliso Canyon gas leak on October 23, 2015. It was reported to be the worst gas leak in U.S. history, with 97,100 tons of methane and 7,300 tons of ethane released into the atmosphere. Comparisons have been made to the equivalent carbon footprint of 1.4m cars or six coal-fired power plants.
The Aliso Canyon leak showed us the important role OGI can play in measuring a leak in terms of how much — something that Method 21 could not do. However, the more OGI is deployed the more practitioners realize that, contrary to what EPA schedules of leak estimates assume, a small number of very large leaks often are responsible for most of the emissions in a defined scope of study. Further, many of the other equipment items are either not leaking at all or have such small emissions rates that they are not economically viable to fix.
Compare this to the inability of the incumbent method of measurement, Method 21, to provide a mass leak rate. You could survey your entire plant and a) not know which leaks are large or small, and b) be unaware of a super-leak coming from a part of your plant not surveyed at all.
This inability to provide data that supports insight into the impact of a leak-repair program, for example in terms of priority, is cause for serious concern. There is growing acceptance that the scenario has led to significant underestimations. Additionally, the idea that 80% of the emissions can be caused by 20% of the leaks has led to about reducing overall emissions totals — if those leaks are not detected and dealt with.
Which way now?
While OGI has been a massive leap forward and broadly welcomed by the industry, one fact remains: an IR sensor cannot provide quantitative information about a fugitive emission. It can only provide a qualitative image of a leak — and one that is periodically apt to either show false positives (e.g., of a moisture vapor cloud) or false negatives (e.g., because of range, focus, shadows or other issues).