methodological developments to define safety criteria

Friday, 17 August 2007

Methodological developments to define safety criteria

Olivier BOUC

3rd IEA GHG Risk Assessment Network Meeting - London


3rd Risk Assessment Network Meeting - London

> 2

Frame of our research

> BRGM research about safety criteria for CO2 geological storage� Internal research project

� 3 years project funded by the National ResarchAgency, with TOTAL, Armines, University Paul Sabatier (Toulouse), University of Neuchâtel

“Safety criteria for CO2 geological storage: qualitative/quantitative approach of risk scenarios”

> Aim: contribute to demonstrating safety of CO2 geological storage

> Safety criteria � performance objectives



> 3

Safety criteria

> Requirements to ensure near-zero local impacts on health, safety and the environment in the short, middle and long term� Qualitative / generic

� Quantitative / site specific



> 4

Purpose

> Provide a simple workflow to evaluate safety in a licensing process� Build long-term evolution scenarios

� Evaluate potential targets exposure using simple models

� Determine safety criteria

> Not a risk assessment� Rather keys to control a risk assessment

> First choose a method to build scenarios� Methodological exercise to try the use of FEPs



> 5

Context of the assessment

> Hypothetical storage site

> In the East of the Paris Basin� Strategic aquifer at -800m

> In the Dogger aquifer� -1700m, thickness 25m

� Nearly flat reservoir, very slow natural flow (1m/yr)

� Near hydrostatic stress state

� � ~ 16% ; K ~ 1 D ; T ~ 55-75°C ; P ~ 173 bars

4- GroupingWhich EPs do present similarities?

1- IdentificationWhich FEPs do enter the frame of analysis?

EPsCharacterised Fs

2- EvaluationProbability / Potential impacts

EPs and associated risk level

Excluded FEPs

Interaction matrix / influence diagram

between EPs groups

6- InteractionsWhich interaction intensity between EPs Groups?

7- Alternate scenarios constitution

Alternate scenarios composed by EPs

groups and related Fs

5- F-EPs CorrelationWhich Fs linked to which EPs groups?

Fs linked to EPs groups

3- SelectionDepending on the risk level determined

Alternate scenarios EPs

Screened out EPs

Reference scenario EPs

Reference scenario

EPs Groups

FEPs database workflow used

• Quintessa

online FEPs

database

• Workflow

closely inspired

by Vattenfall &

TNO « Safety

assessment of

structure

Schweinrich »

in CO2STORE



> 8

Results: six leakage scenarios identified

1

2 33

45

6

1 Well degradation

2 Cap rock fracturing due to overpressure

3 Leakage through buoyancy

4 Leakage through a fault

5 Reservoir water migration

6 Open hole leakage

Saline water migration

Aquifer regional flow

CO2 migration

Pressure front propagation

Overpressure

Fault

CO2 injection well

Hydrocarbons extraction well

Observation well

Reservoir

Freshwateraquifer



> 10

Feedback from our attempt

> Method not optimal� Tedious and time-consuming

� Result: very little surprise compared to the investment!

� Very close to the results of the CO2STORE study

> Some steps arguable� OK for steps 1-3 (Identification – Evaluation –

Selection)

� Step 4 (Grouping) determining and questionable: seems very subjective

� Idem for step 7 (Deducing scenarios from influence diagram)

> Results achieved by giving up steps 4-7



> 11

Restrictions

> Only a test – first use of the tool

> Hypothetical site �� lack of real data

> Not an expert panel

> Difference TNO – Quintessa database� TNO maybe more suitable for this method

� But would it really be more time-efficient ?

> Schweinrich case study hypotheses close to ours



> 12

Feedback (2)

> Main advantages of the FEPs� Comprehensiveness

� Systematic documentation of the evaluation

> Is this really appropriate in our approach?

> Maybe not a scenario-building tool?

> Rather an audit tool� “Top-down” use

� Cf. Quintessa document (Savage et al.[2004], A generic FEP database for the assessment of long-term performance and safety of the geological storage of CO2)



> 13

Possible scenario construction methods

> Non-FEPs approaches:� GEODISC (Australia): an expert panel reviews a

limited number of risk events (probability/impacts)

> FEPs approaches� Battelle, Mountaineer (USA): more qualitative and

quick screening of the FEPs DB. Decision oriented for risk management.

> Mixed approach:� Identification of simple scenarios by an expert panel

� Audit with the generic FEPs database



> 14

Further work and perspectives

> Base safety criteria on potential targets> Develop a site model representing the

potentially exposed elements> Link risk scenarios to targets exposure> Build simple models to evaluate CO2

fluxes between compartments� Analytical, semi-analytical, 1D

� How to ensure they are representative?

� Address uncertainties

> Infer safety criteria

10 km

CO2 injection well

Oil extraction well

Facility where CO2 is produced and captured

River

City: economic activity and living area

Site with nature conservation measures

Site with heritage protection measures

Observation well

Zone widely devoted to agricultural land use

Site model

for CO2 storage in aquifer underneath the

Paris Basin

Aquifer regional flow direction

Fault

NB : local topography is overstated in comparison to the scale for subsurface depth

Potential CO2 leakages (6 identified scenarios)

31

?

2 5 6

CO2 injection

4

Potentially exposed elements

Reservoir

Aquifer to be preserved

Potable water catchment

methodological developments to define safety criteria

Documents