2. information. First, the authors show how the measurements can be
used for time-lapse Q-correction to improve 4D inversion and in-
terpretation in an underlying reservoir, and second, they attempt to
integrate the measured attenuation changes with changes in travel-
time to try and separate gas and water saturations in the reservoir.
He et al. present a field trial of time-lapse continuous electromag-
netic profile for monitoring gas reservoir production. The estab-
lished data acquisition procedure, data processing algorithm, and
the inversion-based interpretation have general applicability and
open new avenues for time-lapse electromagnetic monitoring of
oil and gas production.
Krahenbuhl et al. present a feasibility study on the application
of time-lapse gravity as a monitoring tool for a proposed CO2 se-
questration test site. The approach integrates the reservoir property
model and seismic imaging data with surface and borehole gravity
data for improved recovery of the injected CO2.
Roach et al. apply time-lapse processing to two vintages of seis-
mic data acquired prior to CO2 injection at the Aquistore CO2 stor-
age site using a sparse permanent land array. Time-lapse analysis
combined with fluid substitution modeling indicates excellent re-
peatability between surveys, adequacy in imaging of the subsurface,
and that the data should provide the required sensitivity for mon-
itoring CO2 in the reservoir.
Vanorio shows experimental evidence of time-lapse changes in
the transport and elastic properties of the rock frame due to the
chemo-mechanical interaction between fluids injected into the rock
and the rock matrix itself.
Capriotti and Li use time-lapse gravity data to invert for the
permeability distribution of a reservoir. By directly linking the
equations for fluid flow in porous medium to the time-lapse gravity
response, the authors are able to recover meaningful distributions of
permeability.
Reitz et al. present a feasibility study of monitoring steam-
assisted gravity drainage (SAGD) reservoirs using time-lapse gra-
vimetry and gravity gradiometry because advances in these technol-
ogies have made them viable monitoring tools. The results indicate
that under certain conditions SAGD production should produce a
detectable anomaly using both methods, but the level of detail that
can be recovered through inversion is site dependent.
Saul and Lumley present a new nonelastic method to describe
the pressure sensitivity of rock properties, including changes in
grain contact cement, and apply the method to a 4D seismic data
example from offshore Australia. The authors show that high-pres-
sure water injection may mechanically weaken the poorly consoli-
dated reservoir sands in a nonelastic manner, allowing them to
explain observed 4D seismic signals that are larger than can be pre-
dicted by purely elastic rock-physics theory.
White et al. use repeated 3D seismic surveys acquired with a
sparse permanent array of buried geophones to assess the level
of data repeatability. Signal-to-noise ratio and overall repeatability
are enhanced by the permanent array.
Young and Lumley discuss the recent development that highly
accurate seafloor gravity data can detect small density changes in
subsurface hydrocarbon reservoirs by precisely repositioning the
gravimeters on the seafloor. The authors use this method to assess
the feasibility of time-lapse seafloor gravity monitoring for the giant
gas fields in Australia’s premier hydrocarbon province and find that
several of these producing gas reservoirs can result in readily de-
tectable gravity signals (>5 μGal) within just a year or so of gas
production.
Doetsch et al. monitor geochemical changes induced by injected
CO2 in a shallow aquifer using time-domain spectral induced
polarization. The time-lapse full-decay induced polarization inver-
sions image the CO2 plume as a decrease in resistivity and an in-
crease in normalized chargeability, and the imaged plume agrees
well with electrical conductivity and aluminum concentration mea-
sured on water samples.
WAii Advances in time-lapse geophysics — Introduction
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