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.