t Netherlands Institute of Applied Geoscience TNO - National Geological Survey How can injected CO 2 be monitored? OSPAR Workshop, Trondheim, November 2004 Barthold Schroot, geophysicist / project manager

t OSPAR Trondheim 2004Monitoring of injected CO22 Outline of this presentation Why do we monitor? What do we mean by monitoring? Techniques available for monitoring What can we expect to see? Examples from: Recent research w/r to underground storage of CO 2 Natural analogues Conclusions

t OSPAR Trondheim 2004Monitoring of injected CO23 Why do we need to monitor? Because we want to be sure that CO 2 stays where we put it (in case of geological storage) Direct environmental concern: ensure that no leakage to shallower levels occurs Economics / Climate Change Objectives: verify the amounts of avoided emissions (Emissions Trading Schemes) we need to ensure that no other undesired effects will occur after subsurface injection Think of geomechanical effects (subsidence or uplift of the surface or the seabed)

t OSPAR Trondheim 2004Monitoring of injected CO24 What do we mean by monitoring? Use techniques that enable us to “see” where the injected volume of CO 2 is sitting (or where it might be moving to) CO 2 escape scenarios

t OSPAR Trondheim 2004Monitoring of injected CO25 Outline of this presentation Why do we monitor? What do we mean by monitoring? Techniques available for monitoring What can we expect to see? Examples from: Recent research w/r to underground storage of CO 2 Natural analogues Conclusions

t OSPAR Trondheim 2004Monitoring of injected CO26 What properties do we measure? Where do we measure? 1) at or near the surface 2) in existing or new boreholes (wells) Monitoring techniques Physical prop. Chemical prop. properties: Geophysical Geochemical method: seismic / acoustic gravimetric others (electric etc.) seabed sediment samples water samples includes for example:

t OSPAR Trondheim 2004Monitoring of injected CO27 Common to all techniques: we are looking for anomalies A ‘baseline’ reference measurement (before the start of injection) is recommendable. Jargon: geophysical anomalies geochemical anomalies Monitoring techniques

t OSPAR Trondheim 2004Monitoring of injected CO28 (Geo)physical techniques at surface A very powerful tool is the 3D surface seismic method (seismic imaging) Repeated surveys : time lapse seismic / 4D seismic => changes in time

t OSPAR Trondheim 2004Monitoring of injected CO29 Physical techniques in wells

t OSPAR Trondheim 2004Monitoring of injected CO210 Geochemical sampling & analysis (at or near the surface)

t OSPAR Trondheim 2004Monitoring of injected CO211 Outline of this presentation Why do we monitor? What do we mean by monitoring? Techniques available for monitoring What can we expect to see? Examples from: Recent research w/r to underground storage of CO 2 Natural analogues Conclusions

t OSPAR Trondheim 2004Monitoring of injected CO212 Sleipner gas field: CO2 injection project Courtesy NPD Location of the Sleipner-East field Northern North Sea Average injection of 1 Mtonnes of CO2 per year Injection started in 1996

t OSPAR Trondheim 2004Monitoring of injected CO213 Sleipner: application of 4D seismic method Courtesy Statoil Storage location

t OSPAR Trondheim 2004Monitoring of injected CO214 Sleipner: repeated 3D surveys reveal presence of CO 2 injected since m 1200 m

t OSPAR Trondheim 2004Monitoring of injected CO215 Changes in acoustic velocity result in different expression on seismic data Low CO 2 saturationHigh CO 2 saturation Seismic velocity (m/s) Shear wave velocity insensitive to saturation or compressibility C of the CO 2 Compressional (P) wave velocities for different compressibilities C of the CO 2 High C Low C

t OSPAR Trondheim 2004Monitoring of injected CO216 Sleipner: seismic data -> geological interpretation and modelling Stacked CO2 saturated layers

t OSPAR Trondheim 2004Monitoring of injected CO217 Sleipner: Seafloor micro-gravity method

t OSPAR Trondheim 2004Monitoring of injected CO218 Sleipner: Instrument fixed on concrete benchmarks at seabed

t OSPAR Trondheim 2004Monitoring of injected CO219 Sleipner: Gravity modeling of assumed 21 million tonnes of CO 2 (5  Gal detectable) Modelled gravity anomaly due to presence of CO2

t OSPAR Trondheim 2004Monitoring of injected CO220 The study of natural analogues: Naturally occurring CO 2 (and CH 4 ) seepage CO 2 bubbles Matra mountains, Hungary E.g. in the EU sponsored 5 th FW project NASCENT about natural analogues for CO2 in the geological environment

t OSPAR Trondheim 2004Monitoring of injected CO221 One part of NASCENT project: monitoring shallow gas and methane seepage in the Southern North Sea In the Netherlands offshore most reports of shallow gas are from the northernmost sector Rational: examining expressions of shallow gas (methane) in the North Sea will result in an assessment of monitoring capabilities, also applicable to monitoring CO 2

t OSPAR Trondheim 2004Monitoring of injected CO222 Marine acoustic and seismic surveys Marine seismic data acquisition Images up the 5000 meters below sea bed Hull mounted or floating single channel 3.5 kHz system (sub-bottom profiler) Images the shallowest tens of meters below sea bed, but also effects in the water column

t OSPAR Trondheim 2004Monitoring of injected CO223 High frequency acoustic (sub bottom profiler data 3.5 kHz sub-bottom profiler data: Seabed pockmark associated with venting of gas (pockmark diameter ~ 40m depth ~ 2m) 3.5 kHz data: Acoustic blanking due to gas saturation of shallow layers

t OSPAR Trondheim 2004Monitoring of injected CO224 Shallow enhanced reflectors on 2D seismic line (example block F7)

t OSPAR Trondheim 2004Monitoring of injected CO225 Multiple of the first gas-sand ?? Shallow enhanced reflectors on 3D seismic survey (example block E17) Shadow zone Phase shift These are seismic anomalies corresponding to gas saturation of shallowest layers.

t OSPAR Trondheim 2004Monitoring of injected CO226 Time-slice at 152 msec Profile from previous slide Shallow enhanced reflectors on 3D seismic survey (example block E17) Glacial Channels?

t OSPAR Trondheim 2004Monitoring of injected CO227 Selected areas in the NASCENT project Area 1 (A11) Area 2 (B13) Area 3 (F3) Acquired new data: Multi-beam echo High frequency (acoustic) sub-bottom profiler data 2D seismic data 60 vibrocores: core description headspace gas analysis => C1, C2 concentrations and isotope analysis (δ 13 C of C1)

t OSPAR Trondheim 2004Monitoring of injected CO228 Multi-beam seabed imaging : vertical resolution is high (cms) Marine acoustic and seismic surveys

t OSPAR Trondheim 2004Monitoring of injected CO229 Vibrocoring method for sea bed sediment sampling (North Sea : 2-5 m depth) Seabed sediment sampling

t OSPAR Trondheim 2004Monitoring of injected CO230 Area 1: A seabed pockmark in block A11 multi-beam image & headspace gas analysis 1.Multi-beam image shows seabottom morphology: depression = seabed pockmark 2.Geochemical analysis: ppm CH4 represents a geochemical anomaly

t OSPAR Trondheim 2004Monitoring of injected CO231 Area 2: Gas plumes in the water column example from block B13 Anomaly: up to 10,395 ppm methane in seabed sediment

t OSPAR Trondheim 2004Monitoring of injected CO232 Gas plumes in the water column example from block B13 (area # 2) High frequency sub-bottom profiler record (TNO, 2002): Active venting observed in block B13 over a Plio-Pleistocene shallow gas field Associated : geochemical anomalies (up to 10,395 ppm methane)

t OSPAR Trondheim 2004Monitoring of injected CO233 Underlying Plio-Pleistocene shallow gas field (block B13) Bright spot Miocene unconformity plume

t OSPAR Trondheim 2004Monitoring of injected CO234 Area 3: block F3 various subsurface indications for gas Legend: C1 concentrations in headspace (black) δ 13 C of C1 in red Key vibrocore numbers in blue

t OSPAR Trondheim 2004Monitoring of injected CO235 Gas leaking along faults and fractures expresses itself on seismic profiles Example from Southern North Sea (Dutch sector)

t OSPAR Trondheim 2004Monitoring of injected CO236 Gas leaking along faults and fractures expresses itself on seismic profiles Example from offshore Nigeria, courtesy Addax Petroleum Ltd

t OSPAR Trondheim 2004Monitoring of injected CO237 Gas chimney seen on seismic data (block F3/F6) Gas Chimney

t OSPAR Trondheim 2004Monitoring of injected CO238 Gas chimney above a Plio-Pleistocene bright spot (gas accumulation) WE 16 parallel seismic lines from a 3D survey Line spacing 250 meters Viewed from north to south 3750m View direction Map view

t OSPAR Trondheim 2004Monitoring of injected CO239 Velocity pull-down Chimney 1000m Gas chimney above Pliocene bright spot (Dutch offshore), indicating leakage to the seabed; expression on profiles 100 m 400 m Pliocene shallow gas accumulation (~ 500 m)

t OSPAR Trondheim 2004Monitoring of injected CO240 Gas chimney above Pliocene bright spot (Dutch offshore), indicating leakage to the seabed; expression in map view

t OSPAR Trondheim 2004Monitoring of injected CO241 Outline of this presentation Why do we monitor? What do we mean by monitoring? Techniques available for monitoring What can we expect to see? Examples from: Recent research w/r to underground storage of CO 2 Natural analogues Conclusions

t OSPAR Trondheim 2004Monitoring of injected CO242 Conclusions Various geophysical and geochemical monitoring techniques can be applied to reveal the presence of gas (CO 2 or CH 4 ) in the subsurface Of these techniques 4D seismic monitoring is a very powerful method (covering large areas with high resolution) In case of leakage to the surface techniques exist to measure quantities and fluxes Geophysical techniques can be used for ‘early warning’ With geochemical techniques (at surface or in wells) more acurate quantifications can be made Each case requires a site-specific monitoring strategy depending on an initial risk analysis and on subsurface modelling How frequently and for how long a period should we monitor ? Should we go for permanent monitoring systems ?