Evaluation of CO2 storage actuarial risk: defining an evidence base

Transcription

1 DEVEX 2011, 12 th May, Aberdeen Evaluation of CO2 storage actuarial risk: defining an evidence base Neil Burnside Mark Naylor School of Geosciences University of Edinburgh

2 Outline The evolving risk profile What proportion of CO2 will remain in a formation? Geological security mechanisms Residual saturation trapping Modelling leakage scenarios Varieties of leakage model Gaps What do models show us? Opportunities for further development Summary

3 The evolving risk profile Decreasing risk -> - Geological trapping -Confidence in modelling - Development of monitoring - Pressure recovery LARGE risk = LARGE financial exposure

4 The evolving risk profile Decrease financial exposure LARGE risk = LARGE financial exposure

5 What proportion of CO2 will remain in a formation? Any fraction of CO2 that is securely stored Geological trapping mechanisms - Hydrodynamic - Solubility - Capillary - Mineral - Residual Saturation

6 What proportion of CO2 will remain in a formation? Hydrodynamic -structural & stratigraphic -low permeability -dependant on -distribution -capacity -integrity -orientation CO2 Capture Project Capillary -local -heterogeneity -higher Pc -plume front -diminished buoyancy

7 What proportion of CO2 will remain in a formation? Mineral -carbonate precipitation -Chemical reactions -H + & HCO3 - in solution -mineralogy of rocks (Ca, Mg, Fe) - fluid-rock contact area - fluid velocity Gaus et al. (2006) CO2 Capture Project Solubility -interface with brine -extent of interaction -brine fluid properties -ground water flow -pressure -migration of brine -pressure change in formation

8 What proportion of CO2 will remain in a formation? Residual saturation -Permeability effects - relative gas permeability - maximum CO2 saturation - trapped CO2 saturation - wettability & capillarity

9 What proportion of CO2 will remain in a formation? Timing & interaction - Increase with time & permanently immobilised: - mineral- slow (100 s to 1000 s years) - residual- quick (1 s to 10 s years) - solubility (if ~ zero gw flow)- promotes mineral -Immediate & non-permanent storage: - hydrodynamic -capillary } promote ~horizontal migration and increased interaction with brine and rock IPCC (2005)

10 Residual saturation trapping Occurs over quick timescales and can be measured in the lab Land trapping model (Land,1968) Two and three phase systems Validation of CO2 migration through water wet rocks from both experimental (Land, 1968; Spiteri & Juanes, 2006) and pore network simulation (Spiteri 2005, Juanes et al. 2006) Ratio of S t to S max gives the total fraction of CO2 that is immobilised at the endpoint of the residual trapping process

11 Residual saturation trapping Occurs over quick timescales and can be measured in the lab

12 Residual saturation trapping

13 Residual saturation trapping CO2 relative permeabilities (k r CO2): Uniform distribution over the whole range of possible values Maximum CO2 saturation (S max ): Uniform over a range of Trapped CO2 saturation (S t ): Normal distribution over short range ( )

14 Modelling of CO2 leakage What is being modelled? Varieties of CO2 leakage models Gaps What do models show us

15 What is being modelled? CO2 properties: -volume -density - phases present and phase change - dissolved volume Rock properties: - heterogeneity -porosity - permeability - compressibility - elasticity -mass - tensile strength Temperature and pressure conditions Fault properties: -location -style -angle - permeability - heterogeneity - tensile strength Brine/pore fluid properties: -salinity -density -volume - compressibility - head/flow directions = A LOT OF DIFFERENT PARAMETERS!!! Injectivity: - style/position -rate - pressure increase - hydrofracture? Stress properties: - local stress field - Ϭ1 direction - Ϭ3 direction - past stress fields

16 Varieties of model Assumptions underlying models make their results specific to three categories of leakage: Breakthrough:attempt to estimate and quantify the requirements for CO2 to be able to break through a low permeability confining unit. Steady State:in the event of CO2 migration from the target storage formation these models can be used to determine potential magnitudes and rates of CO2 migration at any geological boundary. Finite Release: investigate how a predefined mass of ascending CO2 would migrate in the subsurface outwiththe storage formation.

17 Varieties of model Varieties of model Breakthrough Geomechanical response Capillary interaction Rutqvist and Tsang 2002 Seyedi et al. (2009) Geochemical interaction Gaus et al. (2006) Hildenbrand et al. (2004)

18 Varieties of model Varieties of model Steady State Saadatpoor et al. (2009) Chang et al. (2009) Grimstad et al. (2009)

19 Varieties of model Finite Release Pruess (2008) Fornel and Vallaure 2009 Viswanathan et al. (2009)

20 Summary of models

21 Gaps Ebigbo et al Semi-analytical: fluid properties constant with time, CO2 & brine immiscible. Numeric: capillary & relative permeability effects, temperature change. Extended: brine = CO2 + water solubility trapping Overall: -Most models very specific -carry a range of assumptions - most scenarios unique -Models generally provide unrealistic results for real life scenarios -Neglect trapping mechanisms and treat CO2 as immiscible - Time TIMESCALES scales of simulation OF SIMULATION Breakthrough: -Miss absolute failure limits Steady State: -Simplified and homogenous leakage pathways Finite Release: -Cover greater range of stratigraphy = forced to simplify rock properties -Simplified vertical leakage pathways.

22 What do models show us? Different model varieties attempt to simulate CO2 behaviour throughout the storage site profile Simplified nature can provide worst case scenarios Caprocks remain competent under upper limits of expected conditions Leakage (to the surface) is found to range from minimal to zero Vertical migration of CO2 from storage reservoir can be effectively contained by attenuation in the overburden Allow for a greater understanding of the causes and thresholds of leakage mechanisms

23 Opportunities for further development Modelling Get more complicated (dependant on computer power and running time) Differences in vertical and horizontal permeability - Optimum permeability distributions for injection and storage Place greater emphasis on the influence of time Incorporate specific and localised simulations into (generic?) large scale system models Grimstad et al (2009)-fit simulation results to analytical expressions

24 Opportunities for further development Investigation of geological trapping mechanisms Efficiencies and contributions of trapping mechanisms Migration of CO2 within the overburden Residual saturation experiments on a range of samples from further locations Investigation of residual saturation at potential storage sites

25 Final summary Residual saturation guarantees immobilisation of % of injected CO2 with 62.5% of samples showing a trapping efficiency of 50% of greater. Increased confidence in security Decreases risk of leakage and therefore financial exposure of CO2 storage operations.

26 Rudra Kapila, Stuart Haszeldine Acknowledgements David Campbell, Paolo Prada