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  • 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 Engineeringemail: pietro.teatini@dmsa.unipd.it , http://www.dmsa.unipd.it/~teatini

  • OUTLINE

    INTRODUCTION

    SITE CHARACTERIZATION

    MATHEMATICAL MODELLINGModelling approachGeomechanics of the mediumGeomechanics of the discontinuities

    RESULTSFailure of the injected formationFailure of the caprochFault activation and induced micro-seismicitySurface displacement

    CONCLUSION

  • INTRODUCTION

    Modelling CO2 sequestration into comparted geological formations:Multi-phase flow and transport processes in porous mediaChemical interactions among gaseous CO2, in situ fluids and solid grainsPoro-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?

  • Main poro-mechanical issues:Activation of existing faults:possible CO2 escapemicro-seismic phenomenaAnalysis 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 CO2Land surface motion:environmental impact of the ground surface heavestructural instability for possible differential displacements INTRODUCTION

  • 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 issuesSITE 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

    SITE LOCATION &PROJECT DESCRIPTION

  • 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 areaConstraints 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 plantSITE LOCATION &PROJECT DESCRIPTION

  • Cross Section with the main formations involved in the Rimini structure modeling3D reconstruction by seismic survey of the complex structure of the Rimini reservoirSurfaces of the top/bottom of the main regional geologic formationsGEOLOGICALSETTING

  • Several info on the geomechanical setting of the basin are available due to the pluri-decadal activities of hydrocarbon exploration and productionSoil compressibility vs vertical effective stress in the Northern Adriatic basin (loading stage) from RMTGEOMECHANICALCHARACTERIZATION

    Overburden / fracturing gradients () and hydrostatic / measured pressure () from well logs

  • MODELLING 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 calculatedThe complexity of the geological system has suggested the use of a simplified modeling approach:

  • MATHEMATICAL MODELLINGGeomechanics of the medium

    Mechanical model of the continuum:Terzaghi-Bishop relationship:Cauchy equations with a constitutive model:withConstitutive mechanical model:Hypo-plastic law with hysteresis:solvedby FE

  • Mohr-Coulomb failure criterion as yield surface: friction angle c: cohesionInterface Elements: special zero or finite thickness elements able to describe slippage or opening of contact surfaces Goodman et al. [1978]MATHEMATICAL MODELLINGGeomechanics of the discontinuities

    Sketch of the RMT technology

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

  • FE IE 2D GRIDFault implementation in the geomechanical model : triangulated surfaces2D Mesh# nodes: 4315# triangles: 8559

  • RiminiFE IE 3D GRID3D Mesh# nodes: 463783# FE: 2868292# IE: 50789(d)

  • Various scenarios have been addressed by the geomechanical model:

    petrophysical model (porosity, horizontal and vertical permeability)only one injection wellpervious lateral boundariesnatural stress regime (compressive vs oedometric)pressure distribution (hydrostatic vs overpressured)yield surface

    Investigated issues:Formation integritySealing capacity of the caprockActivation of the existing faultsMicro-seismicitySea bottom/ground surface motion

    RESULTSScenarios and issues

  • Flow model outcome (i.e. the strength source for the geomechanical simulations):FLOW MODEL OUTCOMEPore overpressureOverpressure profiles at different time steps at injection well W2 vs fracturing overpressurePore 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

  • RESULTSReservoir integrity(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.Shear failure in the injected multi-compartment formation

  • Horizontal view of the safety factors (left) and (right) at the bottom of the caprock sealing the injected formation after 7 years of CO2 injectionRESULTSCaprock integrityEvaluation of possible failure conditions in the caprock bounding the reservoir

  • (above) Modulus of the stress s 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 injectionRESULTSFault activation / Induced seismicityThe 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: M0 is then used to evaluate the magnitude (M) by the equation:G: shear modulus of the host rockds: average slipA : area of the activated faultG = 1.5109 Nm2ds: ~ 1-2 mmA = 104 m2M 1

  • Uplift of the sea bottom/land after 1 year of CO2 injectionRESULTSDisplacement of the ground surface / sea bottom

  • Uplift of the sea bottom/land after 2 years of CO2 injectionRESULTSDisplacement of the ground surface / sea bottom

  • Uplift of the sea bottom/land after 3 years of CO2 injectionRESULTSDisplacement of the ground surface / sea bottom

  • Uplift of the sea bottom/land after 4 years of CO2 injectionRESULTSDisplacement of the ground surface / sea bottom0.12 m 12 cm : quite negligible on account of the 30 m depth of the Adriatic Sea in the area above the reservoir displacement gradient 9 105 : approximately 50 times smaller than the limiting bound acceptable for steel structures

  • 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)

    Conclusions a new larger reservoir is under investigation

  • DICEADepartment of Civil, Emvironmental and Architectural Engineering

    Thank you for your attention

    *

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