Gas hydratws

Gas Hydrates of Russia

Internet Geology News Letter No. 5, August 9, 1999

One volume of gas hydrate can contain up to 220 volumes of gas, suggesting the possibility for exceptionally high concentrations of gas resources at shallow depths. Zones of hydrate do not coincide with zones of permafrost. The tops of the hydrate zones are almost everywhere within permafrost at depths of 200-400 m. The hydrate then extends on below the permafrost to depths of up to 1000 m, favored by temperatures not greater than 10-15 degrees C, elevated formation pressure, and low mineralization of formation water.

Total area of zones of possible gas hydrate formation in the oil-gas regions of Russia exclusive of the Far East is 1,800,000 sq km. This includes 170,000 sq km in Timan-Pechora province, 590,000 sq km in West Siberia province, 376,000 sq km in Yenisey-Anabar province, 374,000 sq km in Lena-Vilyuy province, and 285,000 in the rest of East Siberia. Gas hydrates are present also in the northwest part of the Far Eastern Region (Petroleum Geology, vol. 21, no. 2 and vol. 30, no. 1).

Gas hydrate deposits of West Siberia are discussed here. First, the permafrost. Three zones are present. A zone of continuous permafrost extends from Kara Sea southward to approximately latitude of Salekhard. There it splits into two layers separated by 20-100 m of thawed rock, the upper layer extending from the surface to depths of 30-80 m, and the lower (a relict of earlier glaciation) at depths of 250-400 m. Then farther south is a third zone where only relict permafrost is present.

The zone of gas hydrate formation extends over the northern half of the West Siberian oil-gas province. Depth to its top is 200-500 m, standing highest along the middle course of the Ob River. None is found at depths less than 200 m. Bottom of the hydrate zone is at depths of 400-1000 m, and its thickness ranges from zero to 500-600 m.

Messoyakha gas field in the Cenomanian Stage in the northeast of the province is said to be the first gas-hydrate field in the world to be produced. This field was developed to supply gas to the Noril'sk mine and smelter. The pool is divided into two parts: hydrate-bearing above and gas-bearing below. Gas, hydrate, and water occur in phase equilibrium in the hydrate-bearing part. Similar gas-hydrate pools are possibly present at Zapadno-Messoyakha and Vostochno-Messoyakha (West and East Messoyakha). Gas resources at Zapadno-Messoyakha are assessed at 1-2 tcf, and at Vostochno-Messoyakha - 2-4 tcf.

The Greater Urengoy region appears to be very favorable for exploration for commercial gas hydrate. Thickness of the zone thermodynamically stable for hydrates is as much as 300400 m, and the top is at depths of 200-250 m. Thickness of the permafrost seal is 200-250 m. The large Cenomanian gas pools are 600-700 m below the base of this zone of possible hydrate (Petroleum Geology, vol. 30, no. 4, 1996 and vol. 31 no. 4, 1997)