Content: 1. Principal task in EGS development 2. A methodology: - PowerPoint PPT Presentation

A Methodology for the Hydro-mechanical Characterisation of EGS reservoirs Session: Reservoir characterisation during stimulation Content: 1. Principal task in EGS development 2. A methodology: HEX-S code 3. Example: Coso geothermal field, USA 4. Example: Europ. EGS project Soultz, France Mégel Th., Kohl Th. GEOWATT AG, CH-Zürich ENGINE Workshop3: Stimulation of reservoir and induced microseismicity 29-30th June 2006, CH-Zürich

Principal task in EGS development Life cycle C Exp D Production A phases Production [MWh] 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 Year 2 Principal Tasks: 1. Maximise production 2. Guarantee production Reservoir parameters of production ?

Principal task in EGS development Production Q [l/s] = Function of permeability k(x,y,z,t) Reservoir impedance T [°C] = Function of permeability k(x,y,z,t) Heat exchange surfaces Fractured reservoir permeability k(x,y,z,t) Flow entry Flow exit ? Characterising the reservoir Conditioning the reservoir = Identifying k(x,y,z,t) = Creating/modifying k(x,y,z,t) Strong interrelation of knowledge Tests/measurements/data analysis Stimulation

Data for characterising an EGS reservoir Phase Borehole scale Reservoir scale Before drilling Regional/local geological model Geophysical survey data After drilling Cuttings ( z ) UBI/ARI... logs ( z ) Temp logs ( z ,t) Stress field ( z ) Flow log ( z ,t) After hydraulic tests Pressure (z, t ) 1. well After stimulation Pressure (z, t ) Microseismic locations ( x,y,z,t ) 1. well Hydro-mechan. Physics Identifying k(x,y,z,t) 2. well Predict k(x,y,z,t) for a stimulation scenario HEX-S 3. well

A methodology: HEX-S code Principal concept of HEX-S 2. Hydromech. calc. of k(x,y,z,t) 1. Hydraulic structure model Identification of hydraulic structures Injection flow (t) foreseen Identification of hydraulic structures Injection flow (t) foreseen from existing data sets from existing data sets Pressure development in Pressure development in timestep t i the reservoir (FE-grid) the reservoir (FE-grid) Mapping of the deterministic Mapping of the deterministic structures to a FE-grid structures to a FE-grid Shearing and opening of fractures Shearing and opening of fractures Mapping of stochastic Mapping of stochastic structures to the FE-grid Adaptation of k(x,y,z,t i ) structures to the FE-grid Adaptation of k(x,y,z,t i ) = k(x,y,z,t=0) in FE-grid = k(x,y,z,t=0) in FE-grid

Example: Stimulation GPK4, development of fracture apertures A methodology: HEX-S code

A methodology: HEX-S code Implementation of hydraulic structures Representation: Circular fracture zones subdivided into circular slip patches Mechanics of fracture aperture a: a = 0 a • by compliance σ + ⋅ n , eff 1 9 σ n , ref ( ) ∆ τ = τ − σ ⋅ Φ + Φ • by shearing tan n , eff basic dil ( ) ∆ τ = = ⋅ Φ U ; a U tan K S dil s by jacking : σ n,eff <0 •

A methodology: HEX-S code Representation of hydraulic structures Example: European EGS project Soultz-sous-Forêts, France + Deterministic fracture zones Stochastic fracture zones GPK2 GPK3 GPK4 data used “known” data: • borehole logs (UBI, T, flow,...) statistical interpretation of • structures from microseismicity “known” data: • others stat. distribution of structure parameters

Example: Coso geothermal field, USA Representation of hydraulic structures -1000 34-9RD2 38 pad 38A-9 z [m] -1500 38B-9 38C-9 -2000 34-9RD2 200 34-9RD2 38A-9 0 38a-9 38B-9 -2500 ] 38C-9 -200 38-9 [ 38C-9 38a-9 38b-9 34-9RD2 -400 38C-9 -3000 500 0 x [m] 0 38b-9 y [m] 38-9 -600 -500 -200 0 200 400

Example: Coso geothermal field, USA Representation of hydraulic structures • Dip, Azi of dip, depth Network of hydraulically • Shear friction angle (31°) active fracture zones • Shear dilation angle (3°) • 90% reference closure stress (30e6 Pa) • Fracture zone density [2e-3 m -1 ] • Fracture zone radii (500 m) • Slip patches radii (40 m) • E-modulus (6e10 Pa) Rock parameters • Poissons ratio (0.25) • shmin (z) Stress field • SHmax (z) (linear function with depth) • Sv (z) • Azi of SHmax (11°) • P (z) Initial hydraulics • Initial permeability: 5e-16 m 2 (defines the initial apertures)

Example: Coso geothermal field, USA Representation of hydraulic structures Task Method 1. Identification of the hydraulic activity 1. Extracting the depth range of zones of lost circulation 2. Extracting depth range of signals (significant deviations in gradient) in temperature logs 3. Others ? 2. Identification of the orientation 1. Extracting dip + azidip from FMS- logs for the depth range of each identified FZ under task 1 2. Determination of the set of orientations with the highest occurrences

Example: Coso geothermal field, USA Representation of hydraulic structures 1. Identification of the hydraulic activity, Pad 38A Temperature gradient Lost circulation zones

Example: Coso geothermal field, USA Representation of hydraulic structures 2. Identification of the orientations

Example: Coso geothermal field, USA Representation of hydraulic structures Deterministic hydraulic structures 34-9RD2 38A/B/C-9 Orientations + depths of deterministic FZ for HEX-S model

Example: Coso geothermal field, USA Representation of hydraulic structures Stochastic hydraulic structures Orientation of all fractures with an Orientations + frequency of all hydraulic active fractures from pad 38 assumed hydraulic relevance, with the sign of the corresponding BH

Example: Coso geothermal field, USA Representation of hydraulic structures Stochastic hydraulic structures red: deterministic structures blue: stochastic structures

Example: Coso geothermal field, USA Transient hydro-mechanical calculation FE-grid for transient hydraulic calc. Each element has a permeability corresponding to the apertures of the intersecting fractures X Y k(x,y,z,t i ) Z -1000 -2000 x3 X Y -3000 38B-9 38C-9 -4000 -4000 -2000 -2000 0 0 38A-9 34-9 RD2 x2 x1 2000 2000 4000 4000 Numerical FE Grid Element size 25m ~340‘000 elements

Example: Coso geothermal field, USA Transient hydro-mechanical calculation Example of pressure field • Strongly anisotropic pressure distribution After 15 hours of injection • Radial field only around injection into 34-9 RD2 point • Pressure envelope oriented along fracture orientation • Pressure wave propagation in areas with highest degree of fracturing Example: 5 stochastic realizations 34-9 RD2 1.2E+07 1.0E+07 8.0E+06 Pressure [Pa] 6.0E+06 4.0E+06 2.0E+06 0.0E+00 0 20000 40000 60000 80000 Time [s]

Example: Coso geothermal field, USA Transient hydro-mechanical calculation Calc. fracture shearing Injection into 34-9 RD2 Colour code = shear displacement (red: big displ.) injection into 34-9 RD2 34-9 RD2

Example: Europ. EGS project Soultz, France Transient hydro-mechanical calculation k(x,y,z) structures • Numerical FE Grid mapping • Element size 25m • deterministically defined ap k(x,y,z,t=0) • ~400‘000 elements • stochastically defined Z X Y GPK2 GPK3 GPK4 -3000 -4000 z -5000 -6000 -6000 -4000 -4000 -2000 -2000 y 0 0 x 2000 2000 4000 4000 Z X Y GPK2 GPK3 GPK4

Example: Europ. EGS project Soultz, France Transient hydro-mechanical calculation GPK3, 2003 At GPK3 Around GPK3 2E+07 100 Z II data : 1.04 II data : 1.01 II modl : 1.20 II modl : 1.25 1.8E+07 90 II data : 0.60 II data : 0.78 II modl : 0.88 II modl : 0.80 Y II data : 1 II data : 0.80 II data : 0.70 1.6E+07 80 II modl : 1 II modl : 0.84 II modl : 0.94 X 1.4E+07 70 1.70E+07 1.60E+07 Flowrate [l/s] d Pdh [Pa] 1.2E+07 60 1.50E+07 1.40E+07 1.30E+07 1E+07 50 1.20E+07 1.10E+07 1.00E+07 8E+06 40 9.00E+06 8.00E+06 7.00E+06 6E+06 30 6.00E+06 5.00E+06 4.00E+06 4E+06 20 3.00E+06 2.00E+06 Measured (depth corr.) 1.00E+06 2E+06 10 Model Flow 0 0 0 100000 200000 300000 400000 500000 time [s] • Fit of downhole pressure history • Flow aligned along seismic structures • Highly non-linear processes • Seismicity connected to zones of high pressure • Permeability variation due to shearing

Example: Europ. EGS project Soultz, France Transient hydro-mechanical calculation GPK3, 2003 Microseis. loc. GPK3 stimulation Fracture shearing in HEX-S model after 1 day injection plan view plan view Similar spatial extension

Example: Europ. EGS project Soultz, France Transient hydro-mechanical calculation GPK4, 2004 Pressure measured Pressure from HEX-S model 2.5E+07 20 100 2E+07 II modl : 6.9-7.4 II modl : 9.7-10.7 90 80 15 1.5E+07 Ref.pressure 45.0 MPa 70 ∆ Pdh [MPa] Qin Omega 60 10 50 1E+07 40 30 5 5E+06 20 10 0 0 0 100000 200000 300000 0 100000 200000 time [s] time [s] Measurements HEX-S prediction ∆ P dh at 30 l/s 15.5 MPa 21 MPa increasing to 45 l/s + 1.05 MPa + 1.5 MPa Maximum P dh at t = 16’600 s at t = 15’500 s general characteristics short transients short transients