The
Effects
of Glaciations on the Petroleum Systems in the
Barents Sea
Fjeldskaar, Willy 1; Amantov, Aleksey 2;
Loetveit, Ingrid F.1
(1)Tectonor, Stavanger, Norway. (2) Marine
geology, VSEGEI, St. Petersburg, Russian Federation.
Glacial climate changes over the last million years have
influenced the distribution of oil and gas reserves, mainly in high latitude
and arctic basins. Hydrocarbon exploration in the Norwegian part of the Barents
Sea has been rather unsuccessful so far
; numerous glaciations during the last 3
million years are regarded to be a major cause for this.
Rapid erosion and subsequent differential uplift and tilting is
commonly envisioned to have led to spillage of hydrocarbons, phase transition
from oil to gas, expansion of gas, seal failure, and cooling of source
rocks.
In addition to glacial erosion, repeated ice and sediment loading had great
influence on and the temperature history, i.e. hydrocarbon maturation
hydrocarbon and migration routes. Detailed control on the glacial history,
glacial erosion and sediment deposition is therefore an important factor for
identification of the remaining hydrocarbon resources in the Barents Sea.
The effects
of glaciations on the temperature regime in a
sedimentary basin can be significant. Glaciations affect the thermal
conductivities of the sediments and the surface temperatures. Both will also
influence the reservoir temperatures. A typical glacial period cycle lasts for
100 000 years, which is sufficient time to lower reservoir temperatures to
depths of 5 km by reductions in mean surface temperatures. Ten glacial periods
could lower the reservoir temperature by up to 10°C. Increased thermal
conductivities due to frozen pore water will also contribute to the cooling of the
subsurface. Subsurface temperatures during a cold (permafrost) glaciation could
be as much as 25°C lower than the subsurface temperatures in a non-glaciated
case.
Glaciers, sediments and erosion act as loads on the Earth’s
surface - positive or negative. Both glaciers and glacial erosion will lead to
significant isostatic tilting of the reservoirs. Glacial erosion leads to
significantly lower sub-surface temperatures, and will thus deactivate source
rock hydrocarbon generation.
Changes in local stresses and associated fluid pressures in petroleum reservoirs generated by glaciers and/or rapid glacial erosion may reactivate or initiate faults and other fractures, allowing oil and gas to escape from reservoirs.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.