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Transcript of 1 Microseismic Monitoring of CO 2 Storage at Weyburn James Verdon University of Bristol, U.K....
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Microseismic Monitoring of CO2 Storage at Weyburn
James Verdon
University of Bristol, U.K.
26.05.2010
Microseismic Monitoring of CO2
Storage at Weyburn
AcknowledgementsNR-Can: Don White
Bristol: Kendall, Wustefeld, Wookey
Leeds: Angus, Fisher, IPEGG
£££££: UKERC, PTRC
2Microseismic Monitoring of CO2
Storage at Weyburn
Motivation for CCS
3Microseismic Monitoring of CO2
Storage at Weyburn
Motivation for CCS
4Microseismic Monitoring of CO2
Storage at Weyburn
Geological CCS IssuesLikely leakage pathways:
Wells. Abandoned and not......Loss of caprock integrity:
Geochemical dissolution.Geomechanical deformation.
Monitoring methods:Geochemical:
Detecting CO2 at the surface
Detecting CO2 breakthrough at wells
Fluid-rock reactions.
Satellite:Ground surface deformation due to pressure increases
Seismics:
Controlled source 4-D – detect spatial extent of CO2
Microseismic – detect fracturing and geomechanical deformation
5Microseismic Monitoring of CO2
Storage at Weyburn
The Weyburn CCS ProjectLocated in Saskatchewan, Central Canada
6Microseismic Monitoring of CO2
Storage at Weyburn
By the numbersCO2 provided by a coal gasification plant in Beulah, North Dakota.
CO2 is pumped via pipeline over 200km.
Storage rate is now ~3 Mtonnes of CO2 per year.
Equivalent to the emissions from 1/2 Million (American, gas-guzzling) cars per year.
7Microseismic Monitoring of CO2
Storage at Weyburn
The Weyburn Reservoir
8
Reservoir found in Paleozoic rocks. Upper dolostone and lower limestone zones. 30-40m thick in total.
Caprocks: Evaporite overlain by shale.
Microseismic Monitoring of CO2
Storage at Weyburn
Enhanced Oil Recovery
9
Producing since the 1950s. 20% of OOIP retreived by conventional measures.
CS/EOR will significantly prolong the life of the field, retrieving an additional 10% of the OOIP
Microseismic Monitoring of CO2
Storage at Weyburn
The Caprock(s)
10Microseismic Monitoring of CO2
Storage at Weyburn
4-D Seismics4-D seismics have dominated the monitoring strategy.BUT, What saturation is yellow???Attempts to match with fluid-flow modelling (c)
11Microseismic Monitoring of CO2
Storage at Weyburn
Microseismics at Weyburn
12
CO2 injection initiated in 2000.
Microseismic monitoring initiated in 2003.
1 downhole array, 8 3-C geophones close to reservoir depth.
CO2 injection in a nearby vertical well initiated Jan 2004.
Several producing wells are nearby.
Microseismic Monitoring of CO2
Storage at Weyburn
Microseismics at Weyburn
13Microseismic Monitoring of CO2
Storage at Weyburn
Questions raised….
Why do events occur near the producing wells, not the injection well?
What do the events above the reservoir signify? Fluid migration into the overburden or just stress transfer?
14Microseismic Monitoring of CO2
Storage at Weyburn
SWS Results from Weyburn
Splitting finds a dominant NW striking fracture set, with a weaker NE striking set.
Match with core sample work, except cores suggest NE set should be dominant.
15Microseismic Monitoring of CO2
Storage at Weyburn
Microseismics and geomechanics
16
Geomechanical modelling allows us to predict where to expect failure.
There is a key link between interpretation of microseismic events and geomechanical modelling.
Shear wave splitting will also be sensitive to stress changes.
We have constructed a simple geomechanical model to represent the Weyburn reservoir.
Microseismic Monitoring of CO2
Storage at Weyburn
Geomechanical Modelling Strategy
Geomechanical model
ELFENCamClay (capped) model:
Confining stress
She
ar s
tres
s
Elastic behaviourShear
failu
re Pore collapse
Pore pressure
Porosity, permeability
Fluid flow simulator
e.g., MOREECLIPSEVIP
Model the reservoir onlyPore pressure, fluid properties
17Microseismic Monitoring of CO2
Storage at Weyburn
Geomechanical ModelSimple, representative model:
18Microseismic Monitoring of CO2
Storage at Weyburn
Geomechanical ModelGas saturation after injection
19Microseismic Monitoring of CO2
Storage at Weyburn
Geomechanical ModelPore pressure changes after injection
20Microseismic Monitoring of CO2
Storage at Weyburn
Fracturing
21
Risk of fracturing is given by the fracture potential:
FP = Q / (2 co cos(φ) + P sin(φ))
Microseismic Monitoring of CO2
Storage at Weyburn
Fracturing
22
Reservoir
Overburden
Fracture potential decreases at the injection wells. Little stress evolution in the overburden.
Microseismic Monitoring of CO2
Storage at Weyburn
Shear-wave splitting
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Storage at Weyburn
A softer reservoir?Core samples can miss the effects of large scale fractures on rock stiffness
24Microseismic Monitoring of CO2
Storage at Weyburn
Fracturing
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Reservoir
Overburden
Fracture potential increases in the overburden above the production wells.
Microseismic Monitoring of CO2
Storage at Weyburn
Shear-wave splitting
26Microseismic Monitoring of CO2
Storage at Weyburn
Discussion“The minimum conditions for site closure and transfer of responsibility includes the conformity of the actual behaviour of the injected CO2 with the modelled behaviour.”
Directive 2009/31/EC of the European Parliament on the geological storage of carbon dioxide.
This work has demonstrated the need to compare models with observed behaviour in order to calibrate them properly.
Geomechanical models can be compared with: downhole pressures, stress measurements, surface deformation, and, induced seismicity.
The seismicity in the overburden is caused by stress transfer as the reservoir is softer than expected - it does NOT represent the migration of fluids in the overburden.
27Microseismic Monitoring of CO2
Storage at Weyburn
Feasibility of Microseismics and CCS
28
Most CCS projects will aim to minimise geomechanical deformation - if so why bother to monitor?
If there is little seismicity occurring, how useful can this technique be?
Microseismics as an ‘early warning’? Like soil gas flux and shallow aquifer chemistry (will regulators require it?).
The need to link with geomechanical modelling to interpret events….
Microseismic Monitoring of CO2
Storage at Weyburn
Feasibility of Microseismics and CCS
29Microseismic Monitoring of CO2
Storage at Weyburn
ConclusionsIn most CCS projects, low rates of microseismicity will be desired. This is what is observed at Weyburn.
Events are located near to the production wells, in the reservoir and overburden.
Shear wave splitting measurements imaged two fracture sets that match fracture sets noted from core work.
Geomechanical models have been developed to improve our interpretation of the induced seismicity. However, the initial model did not match observations.
The initial model did not account for the softening effects of fractures in the reservoir. With a softer reservoir, the model provides a good match with both event locations and shear-wave splitting measurements.
This highlights the need to match model predictions with observation before they are used to assess the security of storage.
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Storage at Weyburn
Future WorkImproved (full field) geomechanical models.
Improved methods of microseismic prediction.
Geochemical effects on mechanical properties.
Links with other indicators of deformation (e.g., surface deformation).
In Salah……
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Storage at Weyburn
Any Questions?
32
http://eis.bris.ac.uk/~gljpv/JPV.html
J.P. Verdon, J-M. Kendall, D.J. White, D.A. Angus, Q.J. Fisher & T. Urbancic, 2010. Passive seismic monitoring of carbon dioxide storage at Weyburn: The Leading Edge, 29(2), 200-206.
Microseismic Monitoring of CO2
Storage at Weyburn