Skifergas er større klimasynder end kul

Skifergas er større klimasynder end kul

Flere steder i Danmark leder man efter gas i dybe skiferlag, men nu peger et nyt amerikansk studie på, at udvindingsmetoden for skifergas medfører så høj udledning af drivhusgassen methan, at gasfyring overhaler kulfyring i udledning pr. produceret enhed.

Dybtliggende skiferlag, der gemmer på store mængder af naturgas, bliver både i USA og Europa set som en vigtig, ny energikilde, der kan erstatte kul.

Men nu tager en ny analyse fra Cornell University i staten New York noget af luften ud af denne vision.

Analysen dokumenterer, at udvinding af skifergas medfører så store udslip af den potente drivhusgas methan, at det samlede CO2-udslip ved forbrænding af skifergas er højere end ved forbrænding af kul.

Læs også: Se hvordan hydraulisk frakturering udvinder skifergas

Ifølge analysens ledende forfatter, professor Robert Howarth fra Cornell University er dette den første grundige analyse af CO2-fodaftrykket fra skifergas:

»Vi har brugt de bedste tilgængelige data og kommer til den konklusion, at skifergas kan være ganske ødelæggende for klimaet; sandsynligvis lige så ødelæggende som kul - eller værre,« siger han til BBC News.

Værre end almindelig naturgas

Rapporten fra Cornell University, som fredag offentliggøres som et læserindlæg i Springer-bladet Climate Change, står i høj grad på skuldrene af en ny rapport fra US Environmental Protection Agency fra 2010.

Denne rapport konkluderer også for første gang, at udslippet af flygtige gasser fra selve udvindingen af ukonventionelle gasforekomster sandsynligvis er større end for konventionelt udvundet naturgas.

Ifølge Cornell-analysen er udledningen af methan, omregnet til CO2 ækvivalenter, mellem 30 og 50 procent større end ved udvinding af konventionel naturgas.

Det betyder samlet set, at produktion af strøm ved hjælp af skifergas udleder 20 procent mere CO2 (ækvivalenter) end ved fyring med kul, hvis man sammenligner udslippene over de første 20 år.

Hvis man i stedet ser på sagen over 100 år, så er udslippet ved forbrænding af de to energikilder af samme størrelse.

Methan strømmer op med vandet

I praksis sker en stor del af methan-udledningen via det vand, som man sprækker klippen op med for at komme ind i naturgassen.

Efter opsprækningen af skiferlagene, der sker under højt tryk, returnerer en stor del af vandet i løbet af de første få dage og bringer store mængde methan med op - faktisk mellem 0,6 pct og 3,2 pct. af totalproduktionen på to konkrete brønde.

Sammen med andre, lignende resultater får det forskerne til at estimere et gennemsnits-tab på 1,6 pct.

Også selve boringerne giver anledning til methanudslip, og i alt anslår man - konservativt - at 1,9 pct. af den totale producerede gasmængde fra brønden slipper ud ved tilbageløb og de nødvendige udboringer. Det tilsvarende udslip fra konventionel gasudvinding er 0,01 pct.

Og når produktionen så kører, slipper der methan ud ved diverse sprækker i udstyr og rutine-udblæsninger af systemet, og endelig giver en eventuel opgradering af gassen samt transport, lagring og distributionstab også anledning til ekstra udslip.

25 gange så barsk for klimaet

Når methan udslip er så afgørende, så hænger det sammen med, at methan er en yderst potent drivhusgas - cirka 25 gange kraftigere end CO2.

Dens opholdstid i atmosfæren er til gengæld kort, og derfor er drivhusgas-påvirkningen 22-43 pct. større for skifergas end for konventional gas over en 20 års horisont, men den er noget lavere 14-19 set i et 100 års perspektiv.

Ifølge rapporten eksisterer der muligheder for at reducere methan-udslippet i de nævnte processer, men industrien har indtil videre vist meget ringe interesse i at anvende dem.

Det er ikke kun i USA, at interessen for skifergas er stor. I Europa er der lovende geologiske forhold, der kan rumme skifergas, og i Danmark er tre selskaber aktuelt i gang med at undersøge mulighederne i den danske undergrund. Det sker i Nordjylland, i Nordsjælland og ved Køge.

I Storbritannien er man også med på vognen.

Her påpeger geolog og forsker Euan Nisbet fra Royal Holloway, University of London, at Howarth og hans team med deres analyse af skifergassens CO2 fod-aftryk stiller vigtige spørgsmål om dette 'nye Bonanza', som han kalder det:

»Jeg tror, at debatten om dette vil blive lang og svarene vil være forskellige for hver skifergasdannelse, men det er vigtigt, at vi tager fat på denne debat,« siger han til BBC.

Dokumentation

Analysen fra Cornell Universitetet

Kommentarer (15)

Det første jeg tænker er at de sidste 2% er udvindingsfirmaerne interesserede i at få fingre i og udnytte og sælge. Måske teknologien kan modnes således udvindingen også inkluderer "sidegevinsten".

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(min [b]frem[/b]hævning:)

[b] VANITY FAIR, June 21, 2010 : A Colossal Fracking Mess[/b]

The dirty truth behind the new natural gas

http://www.vanityfair.com/busi...1006

Early on a spring morning in the town of Damascus, in northeastern Pennsylvania, the fog on the Delaware River rises to form a mist that hangs above the tree-covered hills on either side. A buzzard swoops in from the northern hills to join a flock ensconced in an evergreen on the river’s southern bank.

Stretching some 400 miles, the Delaware is one of the cleanest free-flowing rivers in the United States, home to some of the best fly-fishing in the country. More than 15 million people, including residents of New York City and Philadelphia, get their water from its pristine watershed. To regard its unspoiled beauty on a spring morning, you might be led to believe that the river is safely off limits from the destructive effects of industrialization. Unfortunately, you’d be mistaken. The Delaware is now the most endangered river in the country, according to the conservation group American Rivers.

That’s because large swaths of land—private and public—in the watershed have been leased to energy companies eager to drill for natural gas here using a controversial, poorly understood technique called hydraulic fracturing. “Fracking,” as it’s colloquially known, involves injecting millions of gallons of water, sand, and chemicals, many of them toxic, into the earth at high pressures to break up rock formations and release natural gas trapped inside. Sixty miles west of Damascus, the town of Dimock, population 1,400, makes all too clear the dangers posed by hydraulic fracturing. You don’t need to drive around Dimock long to notice how the rolling hills and farmland of this Appalachian town are scarred by barren, square-shaped clearings, jagged, newly constructed roads with 18-wheelers driving up and down them, and colorful freight containers labeled “residual waste.” Although there is a moratorium on drilling new wells for the time being, you can still see the occasional active drill site, manned by figures in hazmat suits and surrounded by klieg lights, trailers, and pits of toxic wastewater, the derricks towering over barns, horses, and cows in their shadows.

The real shock that Dimock has undergone, however, is in the aquifer that residents rely on for their fresh water. Dimock is now known as the place where, over the past two years, people’s water started turning brown and making them sick, one woman’s water well spontaneously combusted, and horses and pets mysteriously began to lose their hair.

Craig and Julie Sautner moved to Dimock from a nearby town in March 2008. They were in the process of renovating their modest but beautifully situated home on tree-canopied Carter Road when land men from Houston-based Cabot Oil & Gas, a midsize player in the energy-exploration industry, came knocking on their door to inquire about leasing the mineral rights to their three and a half acres of land. [b]The Sautners say the land men told them that their neighbors had already signed leases and that the drilling would have no impact whatsoever on their land. (Others in Dimock claim they were told that if they refused to sign a lease, gas would be taken out from under their land anyway, since under Pennsylvania law a well drilled on a leased piece of property can capture gas from neighboring, unleased properties.)[/b] They signed the lease, for a onetime payout of $2,500 per acre—better than the $250 per acre a neighbor across the street received—plus royalties on each producing well.

Drilling operations near their property commenced in August 2008. Trees were cleared and the ground leveled to make room for a four-acre drilling site less than 1,000 feet away from their land. The Sautners could feel the earth beneath their home shake whenever the well was fracked.

[b]Within a month, their water had turned brown. It was so corrosive that it scarred dishes in their dishwasher and stained their laundry. [/b] They complained to Cabot, which eventually installed a water-filtration system in the basement of their home. It seemed to solve the problem, but when the Pennsylvania Department of Environmental Protection came to do further tests, it found that the Sautners’ water still contained high levels of methane. More ad hoc pumps and filtration systems were installed. While the Sautners did not drink the water at this point, they continued to use it for other purposes for a full year.

[b]“It was so bad sometimes that my daughter would be in the shower in the morning, and she’d have to get out of the shower and lay on the floor” because of the dizzying effect the chemicals in the water had on her, recalls Craig Sautner, who has worked as a cable splicer for Frontier Communications his whole life. She didn’t speak up about it for a while, because she wondered whether she was imagining the problem. But she wasn’t the only one in the family suffering. “My son had sores up and down his legs from the water,” Craig says. Craig and Julie also experienced frequent headaches and dizziness. [/b]  
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Citat "Rapporten fra Cornell University, som fredag offentliggøres som et læserindlæg i Springer-bladet Climate Change, står i høj grad på skuldrene af en ny rapport fra US Environmental Protection Agency fra 2010."

Det hedder vel en "artikel" i et "videnskabeligt tidssrift" - det lyder lidt som om der er tale om et brevkasseindlæg i Alt for Damerne. Desuden er det vel også lidt overflødigt om det er Springer eller Elsevier eller en helt tredie, som udgiver tidsskriftet.

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