25th International Meeting on Organic Geochemistry IMOG 2011

P-307
Basin modelling of the Hammerfest Basin and Loppa High
(Southwestern Barents Sea); investigating the leakage of
hydrocarbons in a glacially influenced marine environment
Enmanuel Rodrigues 1 , Rolando di Primio 1 , Zahie Anka 1 , Daniel Stoddart 2 , Brian
Horsfield 1
1 GeoForschungsZentrum, Potsdam, Germany, 2 Lundin Norway AS, Lysaker, Norway (corresponding
author:rodrig@gfz-potsdam.de)
The Barents Sea has a complex geologic history,
especially during the Cenozoic period, because at this
time the area was clearly influenced by tectonic,
paleoceanographic and paleoclimatic events 1,2 . These
events were determinant as they have caused the
redistribution and leakage of the hydrocarbons in the
system 3 . Present-day accumulations are underfilled
and are known to have leaked in the past; however
the timing and extent of the leakage are largely
unconstrained. This study aims to assess and
quantify the amount of hydrocarbons generated by
the main source rocks in the Barents Sea (focussed in
the Hammerfest Basin and the Loppa High), and
determine the proportion leaked to the hydro- or
atmosphere. The effects of glaciation and
deglaciation, and the formation of gas hydrates
together with their possible destabilization, which also
leads to the sequestration and release of gaseous
hydrocarbons, were included in this study. A
quantification of the amount of hydrocarbons leaving
the system was made for the Hammerfest Basin and
is currently carried out for the Loppa High.
The Hammerfest Basin (HB) model reproduces most
of the known oil and gas accumulations in the area
(Snøhvit, Albatross, Askeladden and Goliat fields),
mainly in the most important reservoir: the middle
Jurassic Stø Formation. The main source rocks for
our models are the Jurassic Hekkingen Formation
and the Triassic Snadd and Kobbe formations. The
phase state in the HB accumulations corresponds
mainly to gas with a thin oil leg, except for the Goliat
field, which is filled with oil and has a very thin gas
cap. According to the volumetrics, the present-day
accumulations in the Stø Fm. unit are around 314
Mton (314 x 10 9 kg) for the liquid phase and around
300 Mton (300 x 10 9 kg) for the vapour phase, with
about 213 Mton (213 x 10 9 kg) corresponding to CH4.
The model predicts a slight overpressure in the main
reservoir (Stø Fm.) during glacial loading. The cyclic
loading and unloading of the basin during glacial and
interglacial periods generated pressure fluctuations
(overpressure) which reached up to 5 MPa in
magnitude.
Our preliminary results allow to investigate how ice
loading and unloading affected the reservoir fill,
resulting in spill and leakage. Also the temporal
variability of gas hydrate stability conditions can be
inferred for the HB model, in the timespan between
1.00 Ma and 11,500 years. Investigation of sediment
surface temperature and depth during the glacial and
interglacial periods shows that during the glacial
periods the shallowest parts of the HB were well
within the gas hydrate stability zone, while during
interglacial periods conditions are generally outside
the stability boundary. Moreover, leakage from the
reservoir is predicted to occur preferentially at the
transition from glacial to interglacial times. Leaking
gas was likely sequestered in gas hydrates below the
decaying ice sheet and then released during the
following marine transgression. Modelled cumulative
lost or leaked volumes of CH4 from the reservoir are
in the range of 200 Mton (200 x 10 9 kg). These results
support the possible sequestration of CH4 in gas
hydrates during the glacial periods in the HB, their
likely destabilization during the interglacials, and the
possible leakage to the surface. Methane is known to
be a potent greenhouse gas and atmospheric
contents have been reported to increase since begin
of the last interglacial 4 . Accordingly, our results
contribute to the understanding of global-paleoclimatic
changes.
References
1. Dimakis, P., B.I. Braathen, J.I. Faleide, A. Elverhøi, and
S.T. Gudlaugsson, 1998, Cenozoic erosion and the
preglacial uplift of the Svalbard–Barents Sea region:
Tectonophysics, v. 300, p. 311-327.
2. Vorren, T.O., G. Richardsen, S.-M. Knutsen, and E.
Henriksen, 1991, Cenozoic erosion and sedimentation in the
western Barents Sea: Marine and Petroleum Geology, v. 8,
p. 317-340.
3. Ohm, S.E., D.A. Karlsen, and T.J.F. Austin, 2008,
Geochemically driven exploration models in uplifted areas:
Examples from the Norwegian Barents Sea: AAPG Bulletin,
v. 92(9), p. 1191-1223.
4. Maslin, M., M. Owen, S. Day, and D. Long, 2004, Linking
continental-slope failures and climate change: Testing the
clathrate gun hypothesis: Geology, v. 32, p. 53-56.
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