Mikhail E Permyakov 1 , Albert D Duchkov 1 , Andrej Yu Manakov 2

1. Possibility of use of the geothermal method to search for scattered hydrates in sub-bottom sediments Mikhail E Permyakov1, Albert D Duchkov1, Andrej Yu Manakov2 1Institute of Petroleum Geology and Geophysics 2Institute of Inorganic Chemistry Siberian Branch of Russian Academy of Sciences Novosibirsk

2. Sub-bottom gas hydrates Favorable P-T-conditions for stable gas hydrate are at a depth of 400 m and more water 1 – phase diagram of methane hydrate; 2 – thermogram; BSR – Bottom Simulating Reflector; ЗСГ – Methane hydrate stability zone; ЗСГО – Methane hydrate stability zone in sediments sedimets Methane hydrates are widely distributed in the upper layer of bottom sediments of deep lakes. They accumulate methane gas from deep fluid flows. The total reserves of methane in hydrate deposits may reach according to some estimates as high as 1013 m3. So the development of geophysical methods for exploration and contouring of the relatively small size hydrate bodies lying under a thick water layer is an urgent task.

4. Suggested procedure of geothermal method of searching the sub-bottom hydrate accumulations 1 – sea (lake) expedition organization; 2 – in-situmeasurements of sediment thermal conductivity using different specific heat power; 3 – detecting irregular features in thermograms (decreasing Т, increasingλ), which show the presence of hydrate; 4 – based on the thermal conductivity measurements contouring the bottom area with hydrate-bearing sediments At least two thermal conductivity measurements using different heat power (Q1 < Q2) should be conducted in situ at the same site. One must pick up the value of Q1 so that heating would not lead to hydrate dissociation. The second measurement should be conducted using heat power that is sufficient to melt the hydrates scattered in the sediment near the probe. Picking up the heat power is determined by water depth and bottom sediment temperature (the deeper water and lower the temperature the more stable hydrate in sediments and more heat is necessary for their dissociacion).

5. sediments without hydrate sediments with hydrates Thermograms acquired while measuring in situ thermal conductivity of sediments in northwestern part of the Black Sea (Kutas et al., 2005)

6. Regular thermogram,  1W/(м·K) Abnormal thermogram, = 3,2 W/(м·K) Black Sea, region of mud volcano Dvurechenskii, the Crimean peninsula. In situ thermal conductivity measurements (R. Kutas, J. Poort et al., 2005).

7. Laboratory setup for simulating hydrate-bearing sediments 1а 1 – high pressure chamber (diameter 4 cm, height 15cm,P - 40 MPa); 2 - thermostat;1a и 3 – thermal conductivity measurement device;4 – PC, 5 – discharge valve; 6 - manometer; 7 – gas cylinder

8. Specimen simulating technique mineral particles water ice gas gas hydrate Chamber is filled with the mixture of quartz sand (~ 200 g) and ice (~3 mass %) and pressurized by methane gas. Tinit = -10ºC, Рinit= 4-7 MPa. Hydrate formation process lasts for 20-30 hrs. The technique yields hydrate-bearing specimens with hydrate content of 2-3 mass%

9. specimen content (% by mass): sand - 96,2; water – 1,6; hydrate - 2,2. specific power of the probe heaterQL = 1,3 W/m.

10. initial pressure~11.2 MPa initialtemperature ~3 °С

11. T = Q/(4·π·λ) Ln[(4·k·t)/(1,7811·r02)] (1) λ = [Q·ln(ti/ti-1)]/[4·π·(Ti – Ti-1)] (2) Q = [λ·4·π·(Ti – Ti-1)]/ln(ti/ti-1) (3)

12. Conclusion: Our experiments and elementary analysis showed that interpretation of two different thermograms that are acquired both for stable and unstable hydrates allows to suggest if there is hydrate in the specimen (sediment) and also to estimate the quantity of dissociated hydrate