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COMPARTMENTALIZATION EFFECT IN GEOLOGIC CO 2 SEQUESTRATION.

COMPARTMENTALIZATION EFFECT IN GEOLOGIC CO 2 SEQUESTRATION. A CASE STUDY IN AN OFF-SHORE RESERVOIR IN ITALY. N. Castelletto, M. Ferronato, G. Gambolati, C. Janna, P. Teatini Department of Civil, Environmental and Architectural Engineering

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COMPARTMENTALIZATION EFFECT IN GEOLOGIC CO 2 SEQUESTRATION.

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  1. COMPARTMENTALIZATION EFFECT IN GEOLOGIC CO2 SEQUESTRATION. A CASE STUDY IN AN OFF-SHORE RESERVOIR IN ITALY N. Castelletto, M. Ferronato, G. Gambolati, C. Janna, P. Teatini Department of Civil, Environmental and Architectural Engineering email: pietro.teatini@dmsa.unipd.it , http://www.dmsa.unipd.it/~teatini

  2. OUTLINE • INTRODUCTION • SITE CHARACTERIZATION • MATHEMATICAL MODELLING • Modelling approach • Geomechanics of the medium • Geomechanics of the discontinuities • RESULTS • Failure of the injected formation • Failure of the caproch • Fault activation and induced micro-seismicity • Surface displacement • CONCLUSION

  3. INTRODUCTION Modelling CO2 sequestration into comparted geological formations: • Multi-phase flow and transport processes in porous media • Chemical interactions among gaseous CO2, in situ fluids and solid grains • Poro-mechanical issues due to the coupling between flow and deformation (continuous medium and discontinuity surfaces) Is the sequestration safe enough? Are there any possible impacts on the ground surface?

  4. INTRODUCTION Main poro-mechanical issues: Activation of existing faults: • possible CO2 escape • micro-seismic phenomena Analysis of the induced stress: • shear or tensile failure in the injected formation with variation of the medium properties • shear or tensile failure in the caprock with generation of cracks and leakage paths for the CO2 Land surface motion: • environmental impact of the ground surface heave • structural instability for possible differential displacements

  5. SITE LOCATION & PROJECT DESCRIPTION Within the European Energy Programme for Recovery (EEPR), ENEL (the largest Italian energy provider) is planning a pilot project to inject underground 1Mt/yr (10% of the plant production) for 10 years Several partners: • ENI : geological data end injection knowledgment • OGS-National Geophysical Institute : specific geophysical interpretation • IFP-Institute Francais du Petrole : flow model (COORES) • Univ. Padova : geomechanical model (GEPS3D) • SAIPEM (Eni) : geochemical issues

  6. SITE LOCATION & PROJECT DESCRIPTION Photo of the DELTA power plant The Po river delta with the location of the DELTA power plant • power production capacity: 2640 MW (8% of the Italian need) • fuel: oil • CO2 production: 10 Mt/yr to be stored into the subsurface by 2 injection wells

  7. SITE LOCATION & PROJECT DESCRIPTION • Constraints from the government and ENI: • off-shore (to avoid problems with the population) • within structures hydraulically • disconnected from CH4 fields • less than 100 km far from the power plant Map of the zone of interest for CO2 injection of ZEPT: existing wells in Northern-Central Adriatic Sea and location of DELTA power plant and of the RIMINI injection area

  8. GEOLOGICAL SETTING Surfaces of the top/bottom of the main regional geologic formations 3D reconstruction by seismic survey of the complex structure of the Rimini reservoir Cross Section with the main formations involved in the Rimini structure modeling

  9. GEOMECHANICAL CHARACTERIZATION Soil compressibility vs vertical effective stress in the Northern Adriatic basin (loading stage) from RMT Overburden / fracturing gradients () and hydrostatic / measured pressure () from well logs cM = 0.01241× σz-1.1342 Several info on the geomechanical setting of the basin are available due to the pluri-decadal activities of hydrocarbon exploration and production cM,loading = 3.5 cM,unloading

  10. MODELLING APPROACH The complexity of the geological system has suggested the use of a simplified modeling approach: • one-way coupling approach (no feedback from geomechanics to fluid dynamics) • the failure analysis is performed in two steps: • a basic geomechanical analysis to calculate injection-induced changes in the stress field • a-posteriori failure analysis using the stress field previously calculated

  11. MATHEMATICAL MODELLING Geomechanics of the medium Mechanical model of the continuum: • Terzaghi-Bishop relationship: • Cauchy equations with a constitutive model: solved by FE with • Constitutive mechanical model: • Hypo-plastic law with hysteresis:

  12. F  slippage  Ks=0  τs no longer transferred F  opening  Kn=0  nno longer transferred slippage  Ks=0  τs no longer transferred MATHEMATICAL MODELLING Geomechanicsof the discontinuities Interface Elements: special zero or finite thickness elements able to describe slippage or opening of contact surfaces Goodman et al. [1978] Mohr-Coulomb failure criterion as yield surface Sketch of the RMT technology φ: friction angle c: cohesion

  13. MATHEMATICAL MODELLING Failureanalysis Hypo-plastic model with a post-processing failure analysis. Easily understandable with the aid of the schematic Mohr representation of the stress state Shear failure safety factor: Tensile failure safety factor: f = 30º, c = 0 bar [Fjaer et al. (2008)]

  14. FE – IE 2D GRID Fault implementation in the geomechanical model : triangulated surfaces 2D Mesh # nodes: 4315 # triangles: 8559

  15. FE – IE 3D GRID 3D Mesh # nodes: 463’783 # FE: 2’868’292 # IE: 50’789 (d) Rimini

  16. RESULTS Scenarios and issues • Various scenarios have been addressed by the geomechanical model: • petrophysical model (porosity, horizontal and vertical permeability) • only one injection well • pervious lateral boundaries • natural stress regime (compressive vsoedometric) • pressure distribution (hydrostatic vsoverpressured) • yield surface • Investigated issues: • Formation integrity • Sealing capacity of the caprock • Activation of the existing faults • Micro-seismicity • Sea bottom/ground surface motion

  17. FLOW MODEL OUTCOME Poreoverpressure Flow model outcome (i.e. the strength source for the geomechanical simulations): Overpressure profiles at different time steps at injection well W2 vs fracturing overpressure Pore overpressure (left) and CO2 saturation (right) distributions after 2 (a, e), 3 (b, f), 4 (c, g), and 10 (d, h) years in a cross section through the two injection wells

  18. RESULTS Reservoirintegrity Tensile failure in the injected multi-compartment formation 7 years (a) Portion of the FE grid where the stress field generated by the CO2 injection is investigated. The thrusts and faults are shown with different colors. (b) Safety factor ψ in the selected portion of the Serena structure after 7 years of CO2 injection. (c) FE where ψ  0, i.e. tensile failure is likely to occur. tensile failure

  19. RESULTS Reservoirintegrity Shear failure in the injected multi-compartment formation 1 year (a) portion of the FE grid where the stress field generated by the CO2 injection is investigated. The thrusts and faults are shown with different colors. (b) Safety factor χ in the selected portion of the Serena structure after 1 year of CO2 injection. (c) FE where χ  0, i.e. shear failure is likely to occur. shear failure

  20. RESULTS Reservoirintegrity Shear failure in the injected multi-compartment formation 2 years (a) portion of the FE grid where the stress field generated by the CO2 injection is investigated. The thrusts and faults are shown with different colors. (b) Safety factor χ in the selected portion of the Serena structure after 2 years of CO2 injection. (c) FE where χ  0, i.e. shear failure is likely to occur.

  21. RESULTS Reservoirintegrity Shear failure in the injected multi-compartment formation 3 years (a) portion of the FE grid where the stress field generated by the CO2 injection is investigated. The thrusts and faults are shown with different colors. (b) Safety factor χ in the selected portion of the Serena structure after 3 years of CO2 injection. (c) FE where χ  0, i.e. shear failure is likely to occur.

  22. RESULTS Reservoirintegrity Shear failure in the injected multi-compartment formation 4 years (a) portion of the FE grid where the stress field generated by the CO2 injection is investigated. The thrusts and faults are shown with different colors. (b) Safety factor χ in the selected portion of the Serena structure after 4 years of CO2 injection. (c) FE where χ  0, i.e. shear failure is likely to occur.

  23. RESULTS Reservoirintegrity Shear failure in the injected multi-compartment formation (a) Pore overpressure versus time, (b) Mohr circle evolution, and (c) stress path on the t-s plane for a FE located in the vicinity of an injection well.

  24. RESULTS Caprockintegrity Evaluation of possible failure conditions in the caprock bounding the reservoir Horizontal view of the safety factors χ (left) and ψ (right) at the bottom of the caprock sealing the injected formation after 7 years of CO2 injection

  25. RESULTS Fault activation / Inducedseismicity The methodology advanced by Mazzoldi et al. (IJGGC, 2012) is followed: • the seismic moment (M0) of an earthquake for a rupture patch on a fault is defined by: G: shear modulus of the host rock ds: average slip A : area of the activated fault • M0 is then used to evaluate the magnitude (M) by the equation: (above) Modulus of the stress τs tangential to the fault and thrust surfaces after 7 years of CO2 injection. (below) Active (red) and inactive (blue) IE: red elements slip due to the stress change induced by the injection G = 1.5×109 Nm2 ds: ~ 1-2 mm A = 104 m2 M ≈ 1

  26. RESULTS Displacementof the groundsurface / seabottom Uplift of the sea bottom/land after 1 year of CO2 injection

  27. RESULTS Displacementof the groundsurface / seabottom Uplift of the sea bottom/land after 2 years of CO2 injection

  28. RESULTS Displacementof the groundsurface / seabottom Uplift of the sea bottom/land after 3 years of CO2 injection

  29. RESULTS Displacementof the groundsurface / seabottom 0.12 m Uplift of the sea bottom/land after 4 years of CO2 injection • 12 cm : quite negligible on account of the 30 m depth of the Adriatic Sea in the area above the reservoir • displacement gradient 9 ×10–5 : approximately 50 times smaller than the limiting bound acceptable for steel structures

  30. Conclusions • the FE-IE mesh accurately reproduce the regional geometry of the geological formations, the horizons bounding the structure and the orientation and extent of the discontinuity surfaces (faults and thrusts) • the geomechanical issues can play a most important role in relation to a safe geological disposal of carbon dioxide in multi-compartment reservoirs • the geomechanical simulations indicate that shear failure in large portion of the reservoir is likely to occur well in advance to tensile failure (independently of the various scenarios investigated in the study) a new larger reservoir is under investigation

  31. DICEA Department of Civil, Emvironmental and Architectural Engineering Thankyouforyourattention

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