HR: 08:15h
AN: GC31A-02    [PDF]
TI: 4D Geophysical Monitoring of the Carbon-dioxide Plume at Sleipner, North Sea: a Status Review
AU: * Chadwick, A
EM: rach@bgs.ac.uk
AF: British Geological Survey, Kingsley Dunham Centre Keyworth, Nottingham, NG12 5GG United Kingdom
AU: Arts, R
EM: r.arts@nitg.tno.nl
AF: TNO-NITG, Princetonlaan 6, Utrecht, 3508 TA Netherlands
AU: Eiken, O
EM: oei@statoil.no
AF: Statoil, Rotvoll, Trondheim, N-7005 Norway
AU: Zweigel, P
EM: peter.zweigel@iku.sintef.no
AF: Sintef Petroleum Reserach, S.P. Andersens Vei 15b, Trondheim, N-7465 Norway
AB: CO2 produced at the Sleipner natural gas field is being injected into the Utsira Sand, a major saline aquifer. The SACS project and its successor CO2STORE, aim to monitor the injected CO2 by time-lapse geophysical methods. Time-lapse (4D) seismic data were acquired in 1999 and 2001, with respectively, 2.35 and 4.26 million tonnes of CO2 in the reservoir. The CO2 plume is imaged as a number of bright sub-horizontal reflections, growing with time, underlain by a prominent velocity pushdown that locally attained 60 ms in 2001. The reflections are interpreted as tuned responses from thin (less 8 m thick) layers of CO2 trapped beneath thin intra-reservoir mudstones and the reservoir caprock. The data show that no detectable leakage of CO2 into the caprock has so far occurred. Seismic modelling aimed at verifying the in situ injected mass of CO2 has utilised both inverse and forward modelling techniques. Recent inverse modelling of the 1999 plume has produced a three-dimensional CO2 saturation distribution that can account for the known injected mass of CO2, within the limits of parameter uncertainty. Signal attenuation effects in the 2001 plume render it less suitable for direct inversion. Synthetic seismic (forward) modelling of a flow simulation of the 2001 plume has produced an acceptable fit to the observed reflectivity, but significant discrepancies with the observed velocity pushdown remain. Signal attenuation is likely to become a more significant factor as the plume grows further, perhaps reducing the efficacy of quantitative seismic verification techniques. Other time-lapse geophysical methods may become increasingly useful at this stage. To this end, an initial seabed microgravity survey has recently been acquired at Sleipner.
DE: 0935 Seismic methods (3025)
DE: 1600 GLOBAL CHANGE (New category)
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting