The theoretical part and the results

All accumulations of gas hydrates in the Sea of ​​Okhotsk are found in the areas of gas bubbles output from the sea bottom. The study of the distribution of methane and other gases in the Okhotsk Sea is based on gas-geochemical method developed by the Laboratory of Gas Geochemistry of POI [1]. This method aims are to identify the gas concentrations in the bottom water and upper layer of sediment. During the study period in the Okhotsk Sea more than 500 gas flares output from the bottom into the water column are discovered. The main gas from the vents is predominantly methane. Close to exits of gas bubbles the methane concentration reaches 20 000 nl / l, which exceeds the background value for more than 200 times. In our opinion, during seismic-tectonic activity in the region the layers of gas hydrate are destroyed and free gas which is stored under a gas hydrate cover migrates up to the surface.

We suggest that gas hydrates may be located under the commercial accumulations of gas. This fact is proved by high flows of methane from the seabed into the water column indicate. Their quantification is forthcoming.

Also during the field research conducted in the Sea of ​​Okhotsk continuous seismic profiling has been carried out to determine the location and structure of the BSR (bottom simulating reflectors). It is known that the lower section of the BSR, under the cover of gas hydrates, free gas deposits may occur. According to seismic data, sediments of the Okhotsk Sea in the upper part of the section are characterized by a contrasting border of the BSR. In the depth range of 60-1000 m multiple violations of subvertical orientation is fixed [3]. This is so-called "gas chimneys" through which natural gas comes from the bottom sediments into the water column. Confirmation of this is that the gas flares are discovered close to some gas chimneys.

It should be noted also that in the Okhotsk Sea gas hydrates are found only in the presence of thick strata of sediment (3000 m) extending from the shelf to the slope containing hydrocarbons.

Confirmation that the formation of gas hydrates is interrelated to oil and gas deposits can be seen in the geological features of oil and gas fields of the Prudhoe Bay and Kuparuk River, Alaska. Gas from deposits of oil and gas of these fields goes up through the zone of faults. In an area favorable for pressure and temperature, the gas hydrate layers are formed, which are both the reservoir and the cover for hydrocarbons.

Fig. Massive gas-hydrate layer (white colour) with the thickness of 35 cm recovered on NE Sakhalin slope.

Conclusion

Thus, by a number of features we can see that hydrate-saturated layers of sediments in the Okhotsk Sea may play the role of an impermeable cover which promotes the formation of hydrocarbon deposits. In our opinion, this phenomenon can be observed in other seas of the World Ocean where conditions are similar to those of hydrate formation in the Okhotsk Sea and on land in permafrost.

References:

1. Obzhirov A.I. Gasgeochemical fields of the bottom layer of the seas and oceans. Moscow: Nauka, 1993. 139.

2. Kurile Okhotsk Sea Marine Experiment (KOMEX II). Cruise Report: RV "Akademik Lavrentyev", cruise 29. Leg 1-2 / Eds. Biebow N., Kulinich R., and Baranov B. Kiel, Germany, 2002. 190 p.

3. Sukhoveev, E.N. Seismic stratigraphy of Gas hydrate deposits of the northeastern shelf of Sakhalin Island \ \ Oceanographic Research: Abstracts. Reports. 5th Conf. Young Scientists POI, 25-29 April 2011, Vladivostok, Russia. Vladivostok: Pacific Oceanological Institute, 2011. S. 76-77.

4. Collett T. Natural gas production from Arctic gas hydrates / / The future of energy gases. US geological survey professional paper. 1993. № 1570. P. 299-311.

Дата добавления: 2015-10-29