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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: The Future of 4-D Reservoir Monitoring: Advances in
Technology for Large Oil and Gas Fields
By
Lamont-Doherty Earth Observatory
Getting more oil out of old fields is the payout
of 4-D seismic
reservoir monitoring. 4-
D combines the analysis of
seismic
acoustic changes occurring over time with
other borehole and surface measurements.
4-D analysis has the ability to track time-dependent
changes such as pressure
changes and production histories. The
result is a coupled model of oil and gas
drainage and a more accurate simulation of
future production.
Evaluating the Subsurface over Time
Using Time-Lapse Seismic
The tools and techniques required to interpret
past acoustic changes that have
occurred in oil and gas fields perform two
essential tasks: 1) normalization of the seismic
images between snapshots taken at different
times, using different equipment and
different geometries of acquisition and then
processed differently at the computer center,
and 2)
interpretation
of the similarities
and differences in the acoustic signature of
oil, gas, and water in the reservoir as they
change over time.
More than twenty oil and gas fields from
(fig. 1, 2) the Gulf of Mexico and the North
Sea are the proving ground for new 4-D
technology developments. These fields
provide contrasts in acoustic response and
seismic
signal-to-noise, often between
reservoirs within the same field, that point
to important lessons for the planning of
future 4-D reservoir monitoring projects.
Conclusions to date are 1) pressure history
often affects
seismic
responses
as significantly as oil/gas/water mix changes and
2) volumetric "region-growing"
is a method to scan multiple
3-D
data
sets for changes at
a fast enough computational
rate to satisfy engineers in
charge of production. Region-growing
is a signal analysis
technique developed for the
detection of differences in
MRIs, CAT and PET scans,
and in anti-submarine warfare.
Region-growing is also very
useful for the isolation of 4-D
seismic
differences that are
meaningful in reservoirs.
Better understanding of the
pattern of drainage to the surface
will allow for better planning
and execution of recovery
programs in the future. Four-D
provides the "killer app" for
impedance inversions, which
are the most likely seismic
attributes that can detect
change over time in reservoirs.
As we get better at 4-D monitoring,
more original oil-in-place will be extracted from producing
reservoirs.
The 4-D Seismic
Reservoir
Simulation Loop
Seismic
inversions will be routinely used
on time-lapse
seismic
data
sets to produce
impedance differences. These become
geostatistical reservoir characterizations
and reservoir simulator
data
to quantify
the variations in fluid saturations with
time. New 3-D finite element models will
be developed to compute synthetic
seismic
responses to differences detected by
the real observations.
Seismic
-to-petrophysical
iterations are added to the simulation
loop. The continual updating of the
loop forms a planning tool for predicting
new drilling targets for recovery of
bypassed oil and gas. Repeated looping of
information leads to planning the time,
spacing, types of receivers and borehole
arrays that will be needed to successfully
monitor the oil and gas fields of the
future.
Figure 1. Production from a Gulf of Mexico well drilled after 4-D evaluation.
Figure 2. The field has added reserves after drilling wells based on 4-D.
End_of_Record - Last_Page 8---------------
Cover photo. 3-D graphic illustration courtesy Roger Anderson, Lamont-Doherty Earth Observatory, New York.