Frozen Gas Hydrates Off New Zealand Holds Substantial Gas Resources

Frozen gas hydrates which lies just below the seabed deep off New Zealand's East Coast may contain a future resource of over 8 trillion cubic feet of natural gas, says Stuart Henrys, a senior research scientist at GNS Science.

Research shows that sheets of gas hydrates, made up of ice-like crystals of water and methane molecules intermixed with sediments, are found over 50,000 sq km from offshore Marlborough to offshore Gisborne.

Dr. Henrys says that New Zealand possesses a world class gas hydrate province from about 600 m depth down to the Hikurangi trench.

There is also an area of gas hydrates about 2,500 sq km known at the south west of the South Island near Fiordland.

Methane gas which comes to the surface along the East Coast sea floor is believed to be squeezed out of the earth’s crust as the Pacific Plate is thrust up along the accretionary margin of the East Coast and begins its slow subduction under the northern half of New Zealand.

A combination of very cold currents near the seafloor and the pressure of seawater above leads to the formation of gas hydrates in sediments under the sea bottom off New Zealand.

Dr Henrys says research so far has pinpointed some "sweet spots" where gas hydrates exist in high concentration such as off Cape Palliser in southern Wairarapa and off Cape Campbell in Cook Strait.

Study of the East Coast margin area suggests about 4% of the whole area is sweet spots (indicated by strong bottom simulating reflections from seismic data). Assuming the hydrates were present in a 10 m thick layer with methane saturation of 30% of the pore space, this might contain about 8.5 to 21 trillion cubic feet of potentially recoverable natural gas.

However Dr. Henrys stated that research carried out last year in the area suggested that these sweet spots may contain much more hydrate than assumed in the earlier calculation.

He says more studies have begun on these sweet spots with 3D seismic surveys and drilling the long-term aim. He estimates gas hydrates research could be handed over to commercially driven investment within the next 10-15 years.