Earth degassing in the Arctic: comprehensive analysis of factors of powerful gas emission in the Laptev Sea

Abstract

Interpretation was conducted for 28 CDP seismic time sections with total length of 5930 km acquired by JSC “MAGE” in the Central Laptev Area, where a zone of powerful gas emission had been discovered earlier. 519 anomalous objects were revealed in near-bottom deposits with an average distance on seismic lines of 11,4 km, potentially connected with accumulations of gas and its migration paths. As a result of comprehensive analysis, for the first time, connection of gas seeps with deep-seated faults in the study area was justified. Highly likely forecast was made that in the area of the discovered seeps (seafloor depths from 50—60 m to 110 m), permafrost and gas hydrates are absent, and the seeps are caused by direct migration of gas from great depths. On the continental slope of the Laptev Sea, a bottom simulating reflector (BSR) was distinguished in CDP seismic sections, associated with the base of gas hydrates.

Permanent Gas Emission from the Seyakha Crater of Gas Blowout, Yamal Peninsula, Russian Arctic

“…In recent decades, studies of the near-surface gas content (shallow gas-depth of few hundred meters) in the land and offshore areas of the Arctic, as well as gas emissions into the hydrosphere and atmosphere have been actively developing. This emission is caused mainly by the climate warming in the postglacial period (the last 15,000 years), having the strongest influence on the Arctic and leading to the degradation of permafrost (PF) [7,18,22,43,44,46,51,57,58]. At the same time, large volumes of gas (mainly methane) are released from or contained within the PF strata, as well as being found under it in a free or hydrated state [3,[5][6][7][8][9][10]12,22,27,28,31,38,[41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]59].…”

“…This emission is caused mainly by the climate warming in the postglacial period (the last 15,000 years), having the strongest influence on the Arctic and leading to the degradation of permafrost (PF) [7,18,22,43,44,46,51,57,58]. At the same time, large volumes of gas (mainly methane) are released from or contained within the PF strata, as well as being found under it in a free or hydrated state [3,[5][6][7][8][9][10]12,22,27,28,31,38,[41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]59]. Furthermore, near-surface gas pools pose threats for the drilling of oil and gas prospecting wells-blowouts and fires often lead to the wreckage of drilling rigs and the deaths of personnel [4][5][6]8,9,[15][16]…”

“…As a result of the CDP seismic data analysis in the Laptev, Bering, Okhotsk, Chukchi and Beaufort seas, 1727 anomalous objects potentially associated with gas saturation of near-bottom deposits were identified along seismic lines, with a total length of about 28,000 km (on average every 16.2 km) [17,21,22]. It has been specified that in the Arctic seas, 75-82% of the uppermost potential gas pools are located at depths of less than 200 m from the bottom [17,21,22]. In addition, near-surface deposits with subaqueous PF have large gas resources in the hydrated state [12,17,21,22,40].…”

“…It has been specified that in the Arctic seas, 75-82% of the uppermost potential gas pools are located at depths of less than 200 m from the bottom [17,21,22]. In addition, near-surface deposits with subaqueous PF have large gas resources in the hydrated state [12,17,21,22,40].…”

Forecast of Distribution and Thickness of Gas Hydrate Stability Zone at the Bottom of the Caspian Sea

“…In addition, dissociation of GH can contribute to global climate warming, since methane is a strong greenhouse gas [16,17]. This is particularly important for the Arctic land and shallow offshore areas, where GH can exist on smaller depths of seafloor due to low temperatures of near-bottom water, and as result of dissociation, gas can partially reach the atmosphere [18,19].…”