Sur­vey re­veals seabed gas hy­drate sys­tem

DEMM Engineering & Manufacturing - - NEWS -

A joint New Zealand-Ger­man re­search team has dis­cov­ered a net­work of frozen meth­ane and meth­ane gas in sed­i­ments and in the ocean near New Zealand’s east coast.

The team is us­ing 3D and 2D seis­mic and echosounder tech­nol­ogy to map both forms of meth­ane within the ocean and be­neath the seafloor.

The area off the North Is­land’s east coast is known to have very large ac­tive land­slides, up to 15km long and 100m thick, and the team set out to dis­cover what is caus­ing them to move.

What they dis­cov­ered was di­rect ev­i­dence of wide­spread gas in the sed­i­ment and ocean, and in­di­ca­tions of large ar­eas of meth­ane hy­drate, ice-like frozen meth­ane, be­low the seafloor.

The team has iden­ti­fied 99 gas f lares in a 50 km2 area, vent­ing from the seabed in col­umns up to 250m high. This is be­lieved to be the dens­est con­cen­tra­tion of seafloor gas vents known in New Zealand. Seis­mic data show that land­slides and faults al­low the gas built up in the sed­i­ment to be re­leased into the ocean.

This dis­cov­ery re­veals a hy­drate and gas field very dif­fer­ent from oth­ers known in New Zealand.

“Pre­vi­ously all gas vent­ing sites have been in deeper wa­ter and as­so­ci­ated with large earthquake faults.” says NIWA ma­rine ge­ol­o­gist and voy­age leader Dr Joshu Moun­tjoy.

“What we have found is high den­sity meth­ane f lares in very shal­low wa­ter, as well as gas build­ing up be­neath a large land­slide and be­ing re­leased along the land­slide mar­gins.”

In a sci­en­tific paper the team pro­posed that these land­slides might be the seafloor equiv­a­lent of glaciers, but with frozen meth­ane in­stead of wa­ter ice, or al­ter­na­tively that pres­sur­ized gas is caus­ing them to pro­gres­sively move downs­lope.

The re­sults from this ex­pe­di­tion in­di­cate that both of these are pos­si­bil­i­ties and pro­vide data to care­fully test these hy­pothe­ses.

The ex­pe­di­tion took the op­por­tu­nity to de­ploy the Ger­man re­search in­sti­tute GEO­MAR’s high res­o­lu­tion 3D seis­mic equip­ment known as the P-Ca­ble from NIWA’s re­search ves­sel Tan­garoa.

“This equip­ment is the best avail­able for imag­ing f luid sys­tems within the seafloor,” says co-leader pro­fes­sor Se­bas­tian Kras­tel of the Univer­sity of Kiel. “The sed­i­ment, rocks and f lu­ids we have mapped here are per­fectly suited to this equip­ment, and the area mapped is one of the big­gest ever mapped with the P-Ca­ble seis­mic sys­tem.”

The work forms part of a larger project fo­cused on un­der­stand­ing the dy­namic in­ter­ac­tion of gas hy­drates and slow mov­ing ac­tive land­slides. Dubbed SCHLIP (Sub­ma­rine Clathrate Hy­drate Land­slide Imag­ing Project), on­go­ing in­ves­ti­ga­tions in the project over the next decade will in­clud­ing drilling into the land­slides them­selves in 2016.

This first part of the project, SCHLIP3D, is a col­lab­o­ra­tion be­tween NIWA, GNS Sci­ence and the Univer­sity of Auck­land from New Zealand, GEO­MAR and the Univer­sity of Kiel from Ger­many, Ore­gon State Univer­sity from the USA, and the Univer­sity of Malta.

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