Abstract: Time-Lapse Seismic Analysis of the North
Sea
Fulmar
Field
JOHNSTON, DAVID H., ROBERT S. MCKENNY, Exxon Production Research Co., and TUCKER D. BURKHART, Pennsylvania State University
Summary
Time-lapse seismic analysis has been applied to two 3-D seismic
surveys acquired over the Central North
Sea
Fulmar
Field
— a
pre-production survey shot in 1977, reprocessed in 1987, and a 1992
survey. The Upper Jurassic reservoirs in the
field
have been under
production since 1982. Water is the main drive mechanism, supported
by flank injection. Although the
field
is currently at over 80%
water cut, there are infill opportunities. Petrophysical analyses
for Fulmar indicate that water replacing oil will result in an
increase in seismic impedance. In addition, a pressure decline of
about 1000 psi during the time between the two seismic surveys will
result in a further impedance increase. These impedance changes are
observed between the two seismic surveys. In order to overcome
inherent differences in the seismic data due to acquisition and
processing differences, the data are equalized and then inverted to
obtain impedance which is then averaged between the top of the
reservoir and the position of the original oil-water contact.
Differences in averaged impedance between the 1977 and 1992 surveys
clearly show the effects of water influx and pressure decline. The
changes observed in the seismic data are overall consistent with
predictions obtained from a full-
field
, history-matched flow
simulation. Differences in details may suggest areas of bypassed
oil. However, data quality is not sufficient to serve as the sole
basis for drilling decisions.
AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah