1 Microseismic Monitoring of CO 2 Storage at Weyburn James Verdon University of Bristol, U.K. [email protected] 26.05.2010 Microseismic Monitoring.

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Microseismic Monitoring of CO2 Storage at Weyburn

James Verdon

University of Bristol, U.K.

[email protected]

26.05.2010

Microseismic Monitoring of CO2

Storage at Weyburn

AcknowledgementsNR-Can: Don White

Bristol: Kendall, Wustefeld, Wookey

Leeds: Angus, Fisher, IPEGG

£££££: UKERC, PTRC

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Storage at Weyburn

Motivation for CCS

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Storage at Weyburn

Motivation for CCS

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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

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Storage at Weyburn

The Weyburn CCS ProjectLocated in Saskatchewan, Central Canada

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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.

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Storage at Weyburn

The Weyburn Reservoir

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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

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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)

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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)

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Storage at Weyburn

Microseismics at Weyburn

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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

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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?

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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.

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Storage at Weyburn

Microseismics and geomechanics

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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

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Storage at Weyburn

Geomechanical ModelSimple, representative model:

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Storage at Weyburn

Geomechanical ModelGas saturation after injection

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Storage at Weyburn

Geomechanical ModelPore pressure changes after injection

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Storage at Weyburn

Fracturing

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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

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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

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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

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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.

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Storage at Weyburn

Feasibility of Microseismics and CCS

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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

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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?

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[email protected]

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