Heat Flow Measurements at the Danube Deep-Sea Fan, Western Black Sea

Abstract

Seafloor heat flow measurements are utilized to determine the geothermal regime of the Danube deep-sea fan in the western Black Sea and are presented in the larger context of regional gas hydrate occurrences. Heat flow data were collected across paleo-channels in water depths of 550–1460 m. Heat flow across levees ranges from 25 to 30 mW m−2 but is up to 65 mW m−2 on channel floors. Gravity coring reveals sediment layers typical of the western Black Sea, consisting of three late Pleistocene to Holocene units, notably red clay within the lowermost unit cored. Heat flow derived from the bottom-simulating reflector (BSR), assumed to represent the base of the gas hydrate stability zone (GHSZ), deviates from seafloor measurements. These discrepancies are linked either to fast sedimentation or slumping and associated variations in sediment physical properties. Topographic effects account of up to 50% of heat flow deviations from average values. Combined with climate-induced variations in seafloor temperature and sea-level since the last glacial maximum large uncertainties in the prediction of the base of the GHSZ remain. A regional representative heat flow value is ~30 mW m−2 for the study region but deviations from this value may be up to 100%.

Black Sea hydrate production value and options for clean energy production

“…63 The average porosity was assumed to equal 0.45 accounting for the general trend of porosity decrease with the depth increase and that the BSR1 depths in the Danube area are >450 mbsf. 64 Although drilling was set to characterize hydrates in channel-levee sediments with favorable conditions for higher hydrate saturation all data suggest no gas hydrate is present at drill sites. the average GHSZ depth of the GHD in the BEEZ is ∼350 mbsf; 60 the shallowest (main) BSR occurs in the area at depths 320-380 mbsf 59 (average 350 mbsf); at a water depth of 765 m (close to the shallowest water depth of the GHD in the BEEZ) the BSR depth is 144 mbsf 63 and only the maximum BSR1 depth in the Danube area is > 450 mbsf.…”

“… 63 The average porosity was assumed to equal 0.45 accounting for the general trend of porosity decrease with the depth increase and that the BSR1 depths in the Danube area are >450 mbsf. 64 Although drilling was set to characterize hydrates in channel-levee sediments with favorable conditions for higher hydrate saturation all data suggest no gas hydrate is present at drill sites. 63 …”

“…the average GHSZ depth of the GHD in the BEEZ is ∼350 mbsf; 60 the shallowest (main) BSR occurs in the area at depths 320-380 mbsf 59 (average 350 mbsf); at a water depth of 765 m (close to the shallowest water depth of the GHD in the BEEZ) the BSR depth is 144 mbsf 63 and only the maximum BSR1 depth in the Danube area is > 450 mbsf. 64 5.3.4. Lateral area of the GHD.…”

Black Sea gas hydrates: safe long terms storage of CO2 with environmentally friendly energy production

“…Riedel et al 77 analyzed in situ heat flow measurements data. They used a heat flow probe to determine the geothermal regime of the Danube deep-sea fan, and gas hydrate occurrences.…”

Bulgarian gas hydrate development program: scientific basis

“…Резултатите от сондиране с MeBo200 от 3 сондажа в РИИЗ на дълбочини до 147,3 mbsf при дълбочини на водата 765-860 m показват среден дълбочинен профил на пористостта със стойности близо до морското дъно до ~0,9, които рязко намаляват до ~0,5 на 20 mbsf и са с малки вариации между 0,4 и 0,5 на дълбочини 40-150 mbsf (Riedel et al, 2021b). Средната пористост приемаме равна на 0,45, отчитайки тренда на намаляване на пористостта с увеличаване на дълбочината и максималните дълбочини на BSR в района от 450 mbsf (Riedel et al, 2021a). Средната дълбочина на BSR приемаме 350 mbsf (Василев, А., 2006).…”