ICE LOADING EFFECTS IN SEDIMENTARY BASINS WITH REFERENCE TO THE BARENTS-SEA

During the late Cenozoic numerous glaciations affected the Svalbard/Ba rents Sea region. Ice thickness reached 1-3 km during peaks of glaciat ion periods, and the frequency of cyclic glaciations was variable spat ially across the region. In order to illustrate the broad impact of ic e loading and unloading on a sedimentary basin like the Barents Sea ba sin, a 2-D study of the evolution of a synthetic basin was performed. A 60-km wide synthetic basin section covers a basin center and margin. The lithologies are shares with a large central sand body in contact with a rich source rock in the deepest pa rt of the basin. The synthet ic basin evolution started at 130 Ma, but emphasis is placed on the de velopment of the last 2.5 My, the glaciation period. Five different ca se histories were run for the last 2.5 My period: a base case without ice sheets forming; a steadily growing ice sheet; cyclic glaciations; and two cases of combined steadily growing and cyclic glaciations affe cting basin center and margin and vice versa. The effects of the diffe rent case histories were recorded as excess pressure development, temp erature development, hydrocarbon accumulation, porosity-permeability c hanges and basin geometry changes. The experiments performed demonstra te that both large ice sheets and, in particular, variability in cycli c glaciation frequency across a basin, have major influences on the ph ysical conditions in the basin and on basin structuring. Among the mos t important effects are leakage of water, oil or gas as a result of ov erpressure development, and associated fracturing and/or flexuring of basement and overlying sediments. Variable frequency of ice loading cy cles across a basin can lead to spatial temperature field distortions and changed hydrocarbon generation rates and oil to gas conversion rat es. This situation can also change hydrocarbon migration pathways, and cause spill and a change in hydrocarbon accumulation amounts in a res ervoir. Another interesting aspect is the leakage of gas which can be trapped under low permeability ice and form gas hydrates. Gas hydrates can reinforce the low permeability barrier under ice during glaciatio n periods and may act as a top seal for hydrocarbon accumulations if c old water still preserves their stability field. (C) 1997 Elsevier Sci ence Ltd.