Simulating leakage through well cement: coupled reactive flow in a micro-annulus

Transcription

1 Simulating leakage through well cement: coupled reactive flow in a micro-annulus Laure Deremble, Bruno Huet, Brice Lecampion, Matteo Loizzo

2 Context of Gas leaks: 2 Field evidence Surface Casing Vent Flow (SCVF) Gas migration (GM).Explained by gas flow through defects Microannulus (inner, outer) Mud channels Cracks Cac s( (?) Existing models of gas leaks based on. Equivalent permeability (i.e. upscaled properties and no defect) Stochastic model (LANL, PU) Full reactive transport model (TOUGHREACT, FLOTRAN, HYTEC) do not address the actual physics of leak dynamic: 10 2 m high defect vs 10-2 m thick cement sheath Nature of defects: micro-annulus, channels No local equilibrium between annular fluid and cement sheath Opening/closing of defects From Celia et al. (2004)

3 Integration: mechanics, flow, chemistry 3 Mechanisms considered for opening () or closing () of annulus: Mechanics: Fracturing / debonding of defects Pressurization of defect Cement Calcite Silica Gel Cement: Cement hydrates carbonation Calcium leaching Gel erosion and deposition Drying shrinkage Crystallization pressure of calcite annulus reactive flow: Water condensation CO 2 bubbling Calcite precipitation and deposition Phase change / heat effects

4 Building a fast wellbore leakage model 4 Modeling strategy: Simplified model for each of relevant mechanism Modules Smart integration of modules (based on dimensional analysis) Decoupling Explicit identification of the pathways Module validation against experiments Governing equations Mechanics: Annulus width (w): w 1 pma H p c M Annular chemistry: Mass balance: Chemical equilibrium constraint: Cement: Front tracking: Annular flow (isothermal, T=f(z)=cst) Pressure: Composition: Z dl k j j dt t Zi t c kj jk f X k j aq sol aq f ( L j, D j, cij, cij ) and Qi g( L0, D0, ci0 ) 2 w V and V p X i V DeX i Qi

5 Scenarios 5 Case 1: Cement reactivity in CO 2 rich environment CO 2 saturated brine and open system CO 2 liquid phase and closed system Case 2: CO 2 rich ih phase annular flow Flow + mechanics Flow + mechanics + cement reactivity Case 3: CO 2 saturated brine annular flow Flow + mechanics Flow + mechanics + cement reactivity

6 Case 1 - Rapid Cement Degradation Model = RCDM 6 RCDM = Simplified model for Portland cement / CO 2 interactions Reactor experiments RCDM Portland Cement Open system + CO 2 saturated brine (Duguid et al.) Closed system + CO 2 rich phase (Rimmele et al.) Dissolved CO2 Silica Gel Calcite Reaction fronts Un-reacted cement Comparison with experiments experiment of 1 year simulation of 1 second (with a standard laptop) L [m mm] RCDM exp. 6 RCDM exp Duguid et al. 4 2 Time [days] Rimmele et al.

7 Case 2 CO 2 rich phase annular flow 7 Annular flow and mechanics: Initial / boundary conditions: Top of defect: z=1000m z=1000m, Pt=1bar, T=10C In defect: geothermal gradient, w 0 = 0 m Bottom of defect: z=0m z=0m, Pt=150bar, T=42C, dry liquid CO 2 Results: Opening of annulus Velocity increase at the top

8 Case 2 CO 2 rich phase annular flow 8 Annular flow + mechanics + cement reactivity: Carbonation of cement sheath Water condensation in annulus Leak rates: Cement reactivity = High at early stages CO 2 sink Low at later stages limited by diffusion

9 Case 3 Brine Annular Flow 9 Initial / boundary conditions: Top of defect: z=1000m, Pt=1bar, In defect: geothermal gradient, w 0 = 0 m Bottom of defect: Results z=0m, Pt=150bar, 100 Brine with CO 2 Time: Layers: 25 d 309 d 931 d SH Calcite Depth [m m] z=1000m z=0m Layers length Ca leakage from cement CO 2 ingress into cement CaCO 3 formation in annulus Degradation fronts [mm]

10 Case 3 Brine Annular Flow 10 Flow and mechanics: Opening of annulus (bottom) Velocity increase (top) opening of annulus related to defect elasticity 1 st order mechanism

11 Case 3 Brine Annular Flow 11 Flow + mechanics + cement reactivity: Layer thicknesses Concentration profile Leak rates: Initial inhibition due to cement reactivity

12 Conclusion 12 Modular simulator based on the integration of 1) cement chemistry, 2) annular 1D reactive flow, 3) defect elasticity. At early time (small time scale): Cement / CO 2 fluids interactions control leak rate. At longer time: Cement buffering capacity limited by diffusion Defect elasticity is a 1 st order parameter for CO 2 leak rate evaluation. Identification of specific mechanisms: micro-annulus opening: wellbore elasticity it micro-annulus closing: calcite precipitation Consistency with field results (Loizzo s talk) Study of different leak scenarios and risk analysis now available with this simulation tool

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14 Additional figures 14 CO 2 rich phase annular flow Fluids density Pressure