Tropomi and fugitive methane emissions - recent insights

The Tropomi sensor on Sentinel 5p offers new insights into fugitive methane emissions in gas producing basins. But it is early days, and there is much to learn. Here I explore some implications of recent findings, integrating the new Tropomi constraints with gas production data from US shakle gas basins including satellite-based flaring estimates.

Tropomi

Methane release from large oil and gas fields can now be monitored from space using the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite.

In a recent study Schneising et al. (2020) concluded that

the average [methane] emissions for the time period 2018/2019 from the five most productive basins in the United States, the Permian, Appalachia, Eagle Ford, Bakken, and Anadarko are estimated to be 3.16±1.13 Mt yr⁻¹, 2.36 ± 0.88 Mt yr⁻¹ , 1.52 ± 0.68 Mt yr⁻¹ , 0.89 ± 0.56 Mt yr⁻¹, and 2.81 ± 0.77 Mt yr⁻¹ , respectively. This corresponds to CH4 leakage rates relative to the associated production between 1.2% and 1.6% for the first four production regions, which are consistent with bottom-up estimates and likely fall below the break-even leakage rate for immediate climate benefit.

The Schneising et al. (2020) study compliments a number of previous studies that have attempted to estimate the emissions associated with shale gas production using a variety of methods (Elvidge et al., 2015; Helmig et al., 2016; R. W. Howarth et al., 2011; Robert W. Howarth, 2014; Robert W. Howarth, 2019; Willyard & Schade, 2019).

Schneising et al. (2020) reference methane emissions rates with respect to the total energy production including both gas and oil. As discussed further below, and as is clearly visible by satellite in basins where oil production drives investment, such as the Bakken and the Permian, a significant proportion of produced shale-gas methane is flared and or vented. In such basins the percentage of vented methane referenced against total gas production is necessarily very much higher than referenced against bulk energy production. Moreover, the bulk sum of the gas flaring as well as direct venting is relevant to the “gas as a bridging fuel” debate (e.g., Robert W. Howarth, 2014) and the central question of the “break even rate” in the quote from Schneising et al. (2020). In addressing the challenges of climate change, there is a moral imperative to ensure the utilisation of all exiting fossil production. The additional cost of supply for presently wasted gas is likely to be small compared to cost in the future of remediating climate impacts.

Figure 1: VIIRS nightlights in Texas and adjacent states, illustrating gas related flares in the Permian and Eagle Ford.

Here I look at the emissions rates in several key US gas basins, in terms of total gas production, by comparing them with production data from publicly available sources, including flaring. While data reporting on flaring in US basins is highly variable (e.g. Willyard & Schade, 2019), the new Tropomi data helps to clarify the venting to flaring ratio - a critical poorly defined parameter relevant to emission trajectories for US shale gas production. I begin with some backround relating to US shale gas production and changes in atmospheric methane concentrations.

US shale gas

The advent of shale gas production in the mid 2000’s has dramatically increased US gas production from ~2000 Bcf per month in 2006 to a peak of ~3500 Bcf per month by the end of 2019, prior to the COVID-19 downturn in early 2020 (Fig. 2).

Figure 2: US gas production, sourced from EIA. b) Cape Grim Observatory CH₄ concentration, ppb., source from CSIRO. c) desasonalised annualised growth rates, US gas procuction (red), CGO CH₄ (blue).

In 2019, annual shale gas production averaged around 500 million tones (CH₄) (see appendix, Fig. A12) and accounted for all the growth in U.S. gas production since 2006. Intriguingly, the onset odf US shale gas production correlates with an increase in the rate of increase of atmospheric methane emissions (Fig. 2b). Fig. 2c shows that in detail the correspondence is quite remarkable, with the rate of increase in atmospheric methane tracking about 1/10^th the rate of increase in US gas production. There relationships exposed by Fig. 2c raise a number of fascinating questions, and provide strong incentives for resolving just how much venting occurs in US shale gas basins, and how the venting varies in time.

Data sources

Production and consumption data for U.S. shale production is comprehensively reported by both state authorities, by the EIA. Flaring data is more scattered, while venting data is generally not reported. The North Dakota Industrial Commission reports production, sales and flaring in the Bakken. Estimates of flaring for the Permian are provided by independent consultants Rystad. Independent estimates of flaring based on analysis of NASA/NOAA Visible Infrared Imaging Radiometer Suite (VIIRS) (Elvidge et al., 2015). At the time of writing, compilations of annual flaring volumes from VIIRS analysis as part of the global flares project are complete for the years 2012-2018, with an accuracy estimated to be ±9.5% (Elvidge et al., 2015).

the Bakken

Like many of the U.S. shale gas plays, oil is the principal commodity driving investment in the Bakken. In 2019, Bakken production accounted to ~ 18.3% of all U.S. tight oil, whereas it accounted for only 2.7% of U.S shale gas production (cf. Figs 12 & 13).

Figure 3: Distribution and volumes gas flaring in the Permian and Bakken for 2018, from VIIRS, in units of Mmcf per day

The Bakken dominates hydocarbon production in North Dakota, which is third largest state oil producer. Monthly data for North Dakota production, sales and flaring in is reported by North Dakota Industrial Commission. Typically about 4-5% of production remains unaccounted for in terms of either sales and flaring.

Figure 4: Bakken gas production, NDGG. EIA bakken production in black line

Figure 5: Bakken

Figure 6: Estimates of gas flaring in the North Dakotan production by quarter, data from NDIC, https://www.dmr.nd.gov/oilgas/stats/Gas1990ToPresent.xls. Diamonds are flaring estimates from VIIRS satellite analysis, for the North Dakota flaring. Crossed square is the projected VIIRS flaring based on historic ratio for the priod 2013-2018.

Table 1 lists the values of production, sales, venting and unaccounted production in million tonnes per year, as well as the proportion of flared and unaccounted production as a percentage of total production.

Table 1: Yearly average North Dakota production data in million tonnes per year.

type	2006	2007	2008	2009	2010	2011	2012	2013	2014	2015	2016	2017	2018	2019	2020	2021
produced	1.31	1.47	1.82	1.91	2.38	3.25	5.39	7.26	9.66	12.18	12.69	14.35	17.95	22.12	20.55	22.07
sold	1.11	1.13	1.19	1.35	1.66	2.04	3.52	4.85	6.6	9.41	10.68	11.85	13.92	16.75	17.45	19.55
flared	0.14	0.29	0.56	0.5	0.65	1.12	1.74	2.23	2.71	2.22	1.46	1.86	3.1	4.28	2.07	1.38
unaccounted	0.06	0.06	0.06	0.06	0.08	0.09	0.13	0.18	0.35	0.55	0.55	0.64	0.93	1.09	1.03	1.14
flared %	10.5%	19.3%	30.5%	26.1%	26.8%	34.1%	32.5%	30.6%	28.6%	18.3%	11.5%	12.9%	17%	19.4%	10%	6.27
unacc. %	4.3%	3.7%	3.5%	3.3%	3.4%	2.8%	2.4%	2.5%	3.6%	4.5%	4.3%	4.4%	5.2%	5%	5%	5.15

Figure 7: NDGC North Dakota unsold production. Dashed line shows volumes adjusted for historic VIIR flaring estimates at ~127% reported the level of gas flaring- see text for further disussion.

VIIRS

The estimates of flaring in the Bakken are consistently higher than the flaring volumes reported by the North Dakota Industrial Commission, by a significant amount. For the period 2013 to 2018, the NVIIR estimates average 127%

The distribution plots (Fig. 8 ) show that the less 13.5% of sites account for 50% of flaring volumes

Figure 8: Cumulative distribution of VIIRS production by sites for 2018.

CO₂-e emissions

For the Bakken, Schneising et al. (2020) estimates total methane venting form all sources across 2018 and 2019 average 0.89±0.56 millions tonnes per year. As shown in Table that is simmilar to wht 1.02 million tonnes average of the “unaccounted” gas. Assuming that the “unaccounted” gas in the North Dakota is a proxy for the venting then we can make an estimate of the CO₂-equivalent budget summing the flared gas as CO₂, assuming 100% efficiency, and the methane venting at an appropriate time scale. Figs 9 & 10 show the CO2-e using global worming potential for CH₄ appropriate to 20 years (x86 CO₂ GWP) and 20 years (x 34 CO₂ GWP)

As flaring is generally not 100% efficient,

Figure 9: Bakken

Figure 10: Bakken

the Permian

The Permian Basin covers parts of Texas and New Mexico.

Figure 11: Distribution and volumes gas flaring in the Permian and Bakken for 2018, from VIIRS, in units of Mmcf per day

Rystad flaring estimates

Rystad estimates an average of over 810 Mmcf per day flaring across 2019 (Fig. ??).

(#fig:fig-ry )Estimates of gas flaring in the Permian by quarter. data sourced from https://www.rystadenergy.com/newsevents/news/press-releases/a-downturn-silver-lining-permian-gas-flaring-has-decreased-and-is-expected-to-fall-further-in-2020/. Diamonds are flaring estimates from VIIRS satellite analysis.

VIIRS flaring estimates

The VIIRS estimates of flaring in the Permian are similar to the flaring volumes reported by Rystad. For the period 2013 to 2018, the NVIIR estimates average 97% Rystad.

Discussion

Appendices

Several other data sets are available.

## EIA {.appendix}

Figure 12: US shale gas production by basin, EIA

Figure 13: US tight oil production by formation, EIA. The Permian includes the Wolfcamp, Spraberry, and Bone Spring Formations

Figure 14: Bakken gas production, EIA