The glacial hydrocarbon pump; Investigating the impact of ice sheet oscillations on offshore hydrocarbon stability and leakage

Objective:

During the last 2.7 million years, the Barents Sea shelf bearing vast amount of hydrocarbons experienced up to 30 cycles of glaciation and deglaciation. Throughout these cycles, grounded ice sheets eroded underlying deposits and rocks, causing exhumation and tilting of hydrocarbon traps. Moreover, ice thickness changes affected hydrostatic and lithostatic pressure gradients within the underlying rocks that control migration of hydrocarbons. Cold-based ice sheets frozen to the substrate increase the load on the lithostatic column, while their warm-based counterparts with a liquid water interface contribute to hydrostatic pressure. The former scenario affects sediment compaction and reservoir porosity, while the latter drives phase changes of pore fill (e.g. formation of gas hydrates). Recently, we discovered that the latest deglaciation some 20,000 years ago caused extensive hydrocarbon gas leakage in several locations across the Barents Sea shelf (Serov et. al., 2017; Andreassen et al., 2017). In this project, we aim to investigate the cumulative effect of up to 30 glaciations and deglaciations on hydrocarbon fluid dynamics in the Barents Sea shelf.

Investigating a history of leakage from hydrocarbon traps is an important aspect for petroleum exploration as it might lead to accumulations in shallower subsurface than anticipated and eventual depletion of deeper reservoirs. Moreover, as intense fluid flow has the potential to reach the water column and atmosphere across large areas, our investigations will be important for assessing long-term methane carbon feedbacks driven by cycles of repeated glaciations.

Figure 1 – location of known major fluid release sites associated with the last deglaciation. Red dotted line shows the ice sheet limits during the Last Glacial Maximum (Patton et al., 2016). Yellow stars indicate locations of preliminary study sites.

References:

Serov, P., et al. (2017), Postglacial response of Arctic Ocean gas hydrates to climatic amelioration, Proceedings of the National Academy of Sciences, 114(24), 6215-6220, doi:10.1073/pnas.1619288114.

Andreassen, K., et al. (2017), Massive blow-out craters formed by hydrate-controlled methane expulsion from the Arctic seafloor, Science, 356(6341), 948-953, doi:10.1126/science.aal4500.

Patton, Hubbard, Andreassen, Winsborrow, and A. P. Stroeven (2016), The build-up, configuration, and dynamical sensitivity of the Eurasian ice-sheet complex to Late Weichselian climatic and oceanic forcing, Quaternary Science Reviews, 153, 97-121,

doi:http://dx.doi.org/10.1016/j.quascirev.2016.10.009.