Phase III - Department of Mines and Petroleum

The GJV have focussed their priorities on the detection of early failure modes in the deep subsurface (in
and around the target reservoir). This is a sensible approach and to some extent, depending on the efficacy
of the deep monitoring tools, reduces the requirement for exhaustive shallow or surface monitoring
deployments.
More specifically, the monitoring strategy is guided by the requirements of the Uncertainty Management
Plan. Provided this is valid, and the highside/lowside outcomes are properly taken into account, then the
overall monitoring plan is largely robust. The major containment risks appear to have been satisfactorily
identified and the strategy of time-lapse 3D/2D surface seismic, observation wells and soil gas
measurements is, in principle, well suited to deal with these risks.
Figure 12 Output from the International Energy Association Greenhouse Gas R&D Programme (IEAGHG) monitoring
selection tool for a simplified Barrow Island (onshore) scenario with ‘basic’ filter. The tools that would normally be
considered essential are highlighted in red.
Time-lapse surface seismic is identified as the key monitoring tool. Its capability is, however, constrained
by the very variable seismic data quality so far obtained across Barrow Island and the stringent land-use
restrictions imposed on surface activities. A major project risk therefore is the significant possibility that
3D surface seismic may not be able to satisfactorily image the CO 2 plume everywhere. The GJV have
evaluated the main seismic quality parameters and a limited seismic pilot study has been carried out to
further optimise the baseline 3D survey and assess repeatability. This is commendable but spatial coverage
of such a test is limited. It is recommended that the report on the seismic pilot study and final specification
for the 3D seismic survey be reviewed in the Phase IV assessment.
The GJV has followed a thorough process in identifying the most suitable technologies and completion
geometries for monitoring saturation and pressure changes in both CO 2 injection wells and observation
(surveillance) wells. Clear, well defined objectives for each monitoring variable (pressure, temperature,
saturation, fluid sampling, etc.) have been documented. These objectives have been reflected in the
Uncertainty Management Plan with initial “signposts” or indicators of lowside and highside project
outcomes identified. These signposts are based on early simulation results and will need to be revisited in
light of the most recent project study findings (i.e., dynamic simulation model, geomechanics, geochemical
and injectivity reports) to ensure they remain reasonable indicators for the implementation of mitigation
plans. The monitoring of saturation and pressure changes in the observation and injection wells will help
calibrate the seismic data and the integration of the seismic and well logging datasets will clearly be
beneficial.
xxxv