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January 2017

Vol. 22, No. 4 Week of January 22, 2017

Research reveals Japanese gas hydrates

Multiple deposits detected off country’s west coast hold huge quantities of natural gas but development potential unknown

ALAN BAILEY

Petroleum News

The latest edition of the National Energy Technology Laboratory’s Fire in Ice publication has reported results from research into subsea methane hydrate deposits off the west coast of Japan. The report says that hydrates have been cored from some of the deposits, thus confirming the presence of the hydrates and allowing some estimates of hydrate quantities.

Methane hydrate is an ice-like solid with methane, the primary component of natural gas, trapped in a lattice of water molecules. The material, which can hold high concentrations of methane, is stable within a certain range of relatively high pressures and low temperatures. The hydrates occur naturally in various parts of the world, in situations where pressure and temperature conditions are appropriate to the material’s stability. The material could become a source of natural gas as fuel, if a workable and economic production technique could be developed - hence Japan’s interest in its methane hydrate resources.

Gas chimneys

The Fire in Ice report says that, unusually, the Japanese deposits are found in huge subsea gas chimneys, features where natural gas has in the past bubbled up through the subsurface rocks and presumably formed hydrates when mixed with water in the cold, relatively high pressure environment below the sea floor. Apparently the gas chimneys have given rise to distinctive mounds on the seabed. Research over the course of several years has revealed the existence 1,742 of these gas chimneys offshore Japan’s west coast and around the island of Hokkaido, at the northern end of Japan. Individual chimneys may be anywhere from a few hundred meters to a kilometer in diameter, the report says.

Downhole logging while drilling into 33 of the chimney structures has indicated that the base of the zone in which methane hydrates would be stable may lie at a depth 100 to 120 meters below the seafloor. An investigation of one presumed hydrate mound using intensive logging while drilling techniques indicated the existence of massive hydrate deposits throughout the gas chimney above the stability zone base. Moreover, the coring of material within multiple gas chimneys resulted in the recovery of 27 hydrate-bearing cores. An analysis of these cores suggests that 35 to 86 percent of the material penetrated at each drill site consists of methane hydrate, the report says.

Successful tests

In 2013 Japan successfully conducted a test involving the production of methane from one of its offshore hydrate deposits by drawing down the pressure in the deposit over a period of a few days. And, according to a Platts report published a few months ago, the country is gearing up for another similar test.

But it appears that researchers are still a long way from proving the possibility of continuously sustained gas production at an economically viable cost.

Methane hydrate deposits occur in vast quantities near the base of the permafrost, onshore in Arctic North America, including under Alaska’s North Slope. In 2007 the drilling of the Mount Elbert methane hydrate stratigraphic test well in the Milne Point unit on the North Slope tested and evaluated a hydrate deposit. In 2008 a depressurization methane hydrate production test in the Mallik well in the Mackenzie River Delta of northern Canada lasted six days. A further production test on the North Slope in 2012, involving the Ignik Sikumi No. 1 well, lasted a record 30 days.

And, intriguingly, methane hydrate disassociation has been credited for sustained gas production from the East Barrow gas field at the western end of the North Slope. If this theory for gas production from the field proves correct, the phenomenon would demonstrate the possibility of continuous gas production from hydrates through depressurization of the hydrate resource.






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