La strategia dei Maya: estrarre gas naturale dagli idrati di metano

Sono più di trent'anni che mi occupo di tecnologia e sono tanti anni che mi sento dire che basta un pò più di tecnologia per risolvere tutti i problemi. Petrolio agli sgoccioli? Riscaldamento globale? Che problema c'è? Un po' di ricerca e sviluppo e tutto si sistemerà.

Bene - ultimamente mi sembra di essere un sacerdote Maya che ha passato la vita a fare sacrifici umani e che continua a sentirsi dire "Tutti i problemi si risolveranno se facciamo un po' più di sacrifici umani. Che problema c'è? Basta far contento il Dio sole".




Questo mi è venuto in mente leggendo questo comunicato - che vi passo in fondo. In sostanza, c'è qualcuno che si è messo a fare ricerca e sviluppo sul modo di estrarre gas naturale dagli idrati di metano. Nel caso non lo sapeste, gli idrati (o clatrati) di metano sono formati da gas naturale intrappolato nel ghiaccio ad alta pressione come risultato dell'attività batterica di molto tempo fa. Ci sono grandi quantità di questi idrati sul pianeta ed è da tempo che si pensa di trovare il modo di estrarne gas in quantità commerciali. Sembrerebbe da questo comunicato che la cosa non sia impossibile; anzi, che lo si possa fare con un buon guadagno energetico; perlomeno per un certo tipo di idrati molto concentrati.

Bene; però con gli idrati c'è un piccolo problema. Il fatto è che il metano è un gas serra molto più potente del biossido di carbonio. Che si sfruttino o no gli idrati, il problema è che con l'aumento della temperatura terrestre, gli idrati potrebbero decidere di auto-estrarsi, ovvero liberare il metano nell'atmosfera via via che il ghiaccio si scioglie. Più metano si libera, più l'atmosfera si riscalda e più velocemente il ghiaccio si scioglie; liberando altro metano. Questo meccanismo genera una reazione quasi esplosiva. E' già successo più di una volta nel remoto passato, e il risultato è stato la catastrofe planetaria: estinzioni di massa, anossia atmosferica, surriscaldamento del pianeta e cosette del genere. Per fortuna, non potremo mai estrarre tutti gli idrati di metano che ci sono, ma anche l'estrazione di una piccola parte potrebbe fare grossi danni e mettere in moto un meccanismo spaventoso che poi non sapremmo più come fermare.

Mi immagino che in questo lavoro sull'estrazione degli idrati ci sia stata gente che ha fatto un bel lavoro, ci si è entusiasmata, anche. E tutto questo per peggiorare il problema, e di molto. Andare a stuzzicare gli idrati per risolvere i nostri problemi energetici non è più intelligente dell'idea dei Maya di risolvere i problemi della loro agricoltura con i sacrifici umani.


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Mining "Ice That Burns"

http://www.technologyreview.com/energy/22756/?nlid=2086

Trapped in molecular cages resembling ice, at the bottom of the ocean and in terrestrial permafrost all over the world, is a supply of natural gas that, by conservative estimates, is equivalent to twice the amount of energy contained in all other fossil fuels remaining in the earth's crust. The question has been whether or not this enormous reserve of energy, known as methane hydrates, existed in nature in a form that was worth pursuing, and whether or not the technology existed to harvest it.

Last Friday, the United States Geological Survey (USGS) announced the discovery of suitable conditions for mining methane hydrates 1,000 meters beneath the seabed in the Gulf of Mexico. Together with Chevron and the U.S. Department of Energy, the USGS discovered the reserve of hydrates in high concentrations in 15-to-30-meter-thick beds of sand--conditions very much like terrestrial methane hydrate reserves, which have already yielded commercially useful flow rates. These deposits are substantially different from the gas hydrates that have previously been discovered in U.S. coastal waters, which exist in relatively shallow waters at the surface of the seabed and have become a concern for climate scientists because of their potential to melt rapidly and release large quantities of methane into the atmosphere.

In the spring of 2008, a joint Canadian-Japanese expedition in Mallik in the Northwest Territories, Canada, established that methane hydrates could be harvested by using a water pump to depressurize a well already drilled into the reserve. This involved lowering the pressure pumping out the water that naturally accumulates in the well. Crucially, it required only 10 to 15 percent of the energy represented by the gas that flowed out of the well, making it a much more viable approach than earlier methods used to harvest hydrates, which involved melting them with warm water. Standard oil and gas drilling equipment was used to reenter an old well drilled to a depth of 3,500 feet and then "refurbish" it by casing the entire well with lengths of steel tubing that cemented into place in order to prevent it from collapsing.

Hydrates require both cold temperatures and high pressure to form; eliminating either condition frees the gas from its icy cage, but past attempts to do this by heating the hydrates proved prohibitively difficult. The Canadian-Japanese expedition successfully produced up to 4,000 cubic meters of gas a day during a six-day trial in 2008 using depressurization.

"I think [the Gulf of Mexico find] and Mallik are two revolutionary events," says Timothy Collett, a geologist with the USGS and one of the world's foremost authorities on gas hydrates.

While no one believes that all of the world's methane hydrates will be recoverable, the scale of global reserves has been described by the U.S. Department of Energy as "staggering." They occur anywhere that water, methane, low temperatures, and high pressure co-occur--in other words, in the 23 percent of the world's land area covered by permafrost and at the bottom of the ocean, particularly the continental shelf.

Increased interest in naturally occurring methane hydrates has been driven by the desire for energy independence from the Middle East and Russia and by the need to find energy sources with less of a potential impact on the climate than coal. (Natural gas produces half as much carbon as coal per unit of energy.) This is reflected by an exponential growth in the number of scientific papers published on the subject per year, according to Carolyn Koh, codirector of the Center for Hydrate Research at the Colorado School of Mines. More than a dozen expeditions designed to harvest or sample terrestrial and marine hydrate reserves have been launched since 2001, not only in the United States and Canada, but also in Japan, Korea, China, and India, according to Collett.

While the USGS has not yet calculated the total size of the potential methane hydrate reserve in the Gulf of Mexico, Collett and his colleagues have calculated the scale of another much more accessible reserve where they hope to perfect the technology required for long-term production of methane hydrates: Alaska's North Slope.

The North Slope is already home to a great deal of conventional oil and natural gas extraction (it's the northern terminus of the trans-Alaska pipeline), and it is, not coincidentally, just a few hundred miles west of Mallik.

The USGS used sophisticated three-dimensional modeling and assessment techniques to estimate the probable amount of recoverable gas from Alaska's North Slope: the median yield was calculated to be 85.4 trillion cubic feet, or four times as much natural gas as the United States uses in a year. The model was built using seismometers that peer into the earth like sonar, listening for the propagation of sound waves generated by a controlled source; recordings of that data can be turned into a complete picture of the size and shape of the hydrate reserves.

"This would be the single largest assessed volume of gas resources in the U.S.," says Collett, who cautions that his calculations reflect only what is technically producible from the field but don't take into account whether or not it will be economical to do so.

Mallik has taught scientists how to produce gas from methane hydrates, and the reservoirs in Alaska's North Slope and the Gulf of Mexico suggest that Mallik is not a unique case. The real challenge, however, will be figuring out how to extract sufficient gas economically. This depends on the proximity of the hydrates to existing pipelines and the price and availability of natural gas: no one will pay to develop new resources, after all, until the old ones have become sufficiently expensive.

To date, none of the world's extraction or assessment attempts have been primarily funded by industry. Companies that have participated in methane hydrate field research in North America include Chevron, ConocoPhilips, and BP.

"The question is, does the industry have the ability to stand on its own without government support?" says Collett. "At some point, they will be, and we think we're now nearing that breaking point."

The United States is not the only country with plans to attempt long-term production tests of methane hydrates. Japan is spending by far the most money on methane hydrate research; it provided most of the funding for the Mallik tests, which were sponsored by the Japan Oil, Gas and Metals National Corporation and by Natural Resources Canada, with field operations by Aurora College/Aurora Research Institute and support from Inuvialuit Oilfield Services.

According to the Center for Hydrate Research's Koh, Japan is investing heavily in attempts to harvest deep-sea hydrate reserves discovered off the southern coast of Japan in the Nankai Trough.

"The Japanese are planning commercial production from the Nankai Trough by 2017," says Koh. If they succeed, Japan will tap the first domestic fossil-fuel reserves the country has ever known.