TA的每日心情 | 慵懒
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本帖最后由 兰凯 于 2014-8-28 21:24 编辑 3 T6 T$ h3 _- m" Q9 o3 q, L$ \
不爱吱声 发表于 2014-8-28 02:24
* H% j+ N7 a% a; g康奈尔那位的文章吧？
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现在气井开采有严格的regulation，天然气开采泄露和烧煤产生二氧化碳是两回事儿， ...
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有关天然气开采泄露的总量的问题似乎还有争议, 并不仅仅是康奈尔的Howarth一人, 这是我最近看到的一个评论：' h$ K' p4 l( v6 a; W
% ^, P0 k8 i ]2 W" M9 b2 |9 \About 29% of U.S. methane emissions are from leakage in the oil and gas production and distribution chain, according to the Environmental Protection Agency’s Greenhouse Gas Inventory. That makes the oil and gas industry the nation’s second-largest source of methane releases, ranking barely a percentage point below emissions from livestock.
3 M. h9 m. ]7 c$ Y; @# ~- ^ T3 @Oil and gas drilling and field production constitute nearly half this loss, according to Paul Gunning, director of EPA’s Climate Change Division in the Office of Air & Radiation, who spoke at a recent webinar. The rest is divided among gas processing, transmission, storage, and distribution.
( [( Q2 q) ^. R' _( ~% \The actual methane leakage numbers—stated as a percentage of production—are between 1 and 2%, according to EPA’s annual inventory, based on the agency’s interpretation of industry-reported data. This number varies yearly and has shown a decline over time, according to EPA’s assessment of industry reports.+ b: P% l, K1 D5 I0 i! W, R
+ T+ g1 R. K( B+ XGlobal methane concentrations remained steady at about 0.7 ppm for hundreds of years, then began to rise quickly during the modern industrial age.NOTE: Data for 1750–1982 are from CSIRO Marine & Atmospheric Research. Data for 1983–2014 are from NOAA.SOURCE: Ed Dlugokencky/NOAA# t3 f4 q* j U
However, many atmospheric scientists question these numbers, saying they are too low, and point to a host of new studies conducted in recent years.
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9 F I$ |+ S" F( j# [First to voice a strong challenge to EPA’s data was Robert W. Howarth of Cornell University. Three years ago, Howarth warned that overall methane emissions from natural gas activities could be 7.9% of production, far above EPA’s calculation. He blamed EPA’s low estimate on missed releases during fracking, when methane and other hydrocarbons flow to the surface, carried up by fracturing fluids when wells are initially drilled and fractured (Clim. Change Lett. 2011, DOI: 10.1007/s10584-011-0061-5).7 z' [1 r" t5 Q- x
1 G, z5 O% H. H/ h& |2 pA study published in 2012 appears to support Howarth. Scientists from the National Oceanic & Atmospheric Administration (NOAA) and the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado, Boulder, accidentally discovered high methane levels being released from a Colorado oil and gas field. They were conducting tower-based air measurement experiments near a freeway (J. Geophys. Res. 2012, DOI: 10.1029/2011jd016360).
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The group continued their methane experiments and shifted to a large oil field in Utah, where they used aircraft to take air samples over natural gas and oil fields in Uintah County. There, the research team, led by Anna Karion, found methane leakage rates of 6 to 12% of production. The study was published last year (Geophys. Res. Lett. 2013, DOI: 10.1002/grl.50811).
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9 |3 D m! k- f3 T, F- B9 | MThis group of researchers also conducted a follow-up study to the earlier one in Colorado and found methane levels that were at least three times higher than EPA’s estimate. Their data were published last month in the Journal of Geophysical Research (2014, DOI: 10.1002/2013jd021272). These studies are highly structured and adjust for other sources of methane near the oil and gas fields, the researchers note.7 T$ V2 Y" Z K8 I. D' ~
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A growing body of literature supports the view that methane emissions are higher than levels reported by industry and EPA. A study released earlier this year by a team led by Adam R. Brandt of Stanford University examined some 20 years of technical literature and 200 papers and found that federal officials have consistently underestimated actual methane emissions, which the report says are some 50% higher than EPA’s estimates (Science 2014, DOI: 10.1126/science.1247045).
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: d# p! x" {' t4 ~ N3 g. zOther peer-reviewed studies have raised similar challenges to EPA’s estimates, all pointing to levels above the agency’s estimates.
* T( Z/ b" h, P/ u3 s2 \However, not all studies found problems in EPA’s data. An examination by scientists at the University of Texas, Austin, backed EPA’s numbers (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1304880110).9 q- p" x1 P2 ?3 D& e2 x- b7 q
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The Texas researchers found methane leakage levels from drilling and production to be near or even slightly lower than EPA’s estimates. The study, funded and organized by the Environmental Defense Fund (EDF), an environmental group, and several oil and gas companies, measured methane emissions from operations on the ground at the oil and gas fields, rather than air measurements taken during flights over the sites.+ k& }0 t, ?7 P" G+ ]
This study is the first in which oil drillers, which control the sites, granted access to nonindustry researchers. Consequently, this study provides on-the-ground measurements. But like EPA’s inventory, it carries the stigma of industry control.5 d: j! D/ F& t. e
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Industry and researchers negotiated to select the test sites, noted David T. Allen, a UT Austin chemical engineering professor, who led the study. Speaking at the webinar, Allen acknowledged that the tests may be measuring best conditions—sites with so-called green completions that use new technologies to capture methane leakage during drilling and fracking. Still this study advances the discussion by measuring on-the-ground emissions, he said.
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0 t6 S: d0 I* C- ZThe difference has been characterized as “top-down versus bottom-up”—field measurements at a specific site versus measurements from above in an aircraft or tower.
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* p; l: F9 Y7 UAllen, Gunning, and other researchers attribute the high losses that NOAA and CIRES found to so-called superemitters—badly run, old, and leaking well sites or abandoned wells from partially depleted fields.
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- F( S- Y8 O$ w" l4 F- E+ xThey stress the difficulty in measuring emission from huge fields holding tens of thousands of operating wells and an unknown number of closed sites. EIA estimates that there are some 500,000 wells operating at some level of production in the U.S.; C: K3 u0 ~/ w. o9 g/ g
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The disparity might be resolved by upcoming research that will merge top-down and bottom-up approaches to emissions measurements. Those studies are just getting under way, notes Drew Nelson, EDF senior manager for natural gas projects. EDF and the gas and oil industry are funding 16 studies involving 90 academic and industry collaborators, and results are expected this year, Nelson says.
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Several of these studies will be done by the NOAA-CIRES team of scientists, says Jeff Peischl, CIRES associate scientist. Their plan, he says, is to conduct top-down measurements of an oil and gas field by aircraft and back up this data with mobile lab measurements on the ground. NOAA-CIRES will use two aircraft and four mobile units and will look for other hydrocarbons as well as methane. The researchers will start these investigations within a month, he adds.
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7 ~& F; s G1 m9 N6 o% d" H/ yBottom-up measurements are difficult, Peischl says, but combining them with top-down measurements may help solve the puzzle. “You find a leaking valve in an oil field and you measure it, but you have to ask—will this be the same for thousands of other valves in a field, or is it just one valve that someone forgot to tighten?”
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Cornell’s Howarth remains convinced of his early argument. In a recent paper, he says that EPA and Allen are “measuring the best possible performance by the industry” by relying on industry data and giving industry control of sampling points. He also stands by his earlier conclusion that natural gas and coal have similar greenhouse gas impacts when methane leakage is included with CO2 from burning methane. He warns that rather than a bridge fuel, natural gas is “a bridge to nowhere” (Energy Sci. Eng. 2014, DOI: 10.1002/ese3.35). |
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雷达卡
发表于 2014-7-19 10:38:04
显身卡
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