Electroseismics for CO 2 storage and hydrocarbon reservoirs. Fabio I. Zyserman

Transcription

1 Electroseismics for CO 2 storage and hydrocarbon reservoirs Fabio I. Zyserman EOST, March 12th, 213

2 Electroseismics: field experiments Thompson et al, 27 Electroseismic response in gas and oil reservoirs from about 15 m depth. Signal between two and six orders of magnitude less than ambient noise. It is necessary to optimize the source power ( megawatt), the injected signal (few thousands A), and the detection equipment (digital accelerometers). EOST, March 12th, 213

3 Electroseismic Modeling I Glover and Jackson, TLE, 21 When an applied electric field acts on an electrolyte saturated porous material, besides driving σe, it acts as a body force on the excess charge, giving rise to a net fluid filtration; this is called electro-osmosis electroseismic phenomena. Reciprocally, an applied pressure gradient generates an electric current; this is called electro-filtration seismoelectric phenomena. EOST, March 12th, 213

4 Electroseismic modeling II Assuming an e +iωt time dependence, Pride (1994) proposed (σ + iɛω)e H + L(ω)ηκ 1 [ iωu f ] L(ω)E = J ext e, E + iωµh = J ext m, ω 2 ρ b u s ω 2 ρ f u f τ(u) = F (s), ω 2 ρ f u s + ηκ 1 [ iωu f ] L(ω)E + p f = F (f ), τ lm (u) = 2G ε lm (u s ) + δ lm (λ c u s + αk av u f ), p f (u) = αk av u s K av u f. φ porosity, ρ s, ρ f solid and fluid densities, ρ b = (1 φ)ρ s + φρ f, η fluid viscosity, κ(ω) dinamic permeability In the constitutive equations λ c = K c 2/3G and K c = K m + α 2 K av, [ α = 1 Km α φ, K av = + φ ] 1. K s K s K f K s, K m and K f : bulk moduli of the solid grains, the dry matrix and the fluid. EOST, March 12th, 213

5 Electroseismic modeling III 2D Sources and Modes Infinite solenoid: Jm ext generates electromagnetic fields (E x (x, z), E z (x, z)), and H y (x, z), coupled with solid displacements (ux(x, s z), uz(x, s z)) and fluid displacements (ux(x, f z), uz(x, f z)). This is the so-called PSVTM-mode, in which compressional and vertically polarized shear seismic waves (PSV-waves) are present. Infinite current line: Je ext generates electromagnetic fields (H x (x, z), H z (x, z)) and E y (x, z), coupled with solid displacements uy(x, s z) and fluid displacements uy(x, f z). This is known as the SHTE-mode, where only horizontally polarized seismic waves (SH-waves) are present. EOST, March 12th, 213

6 Electroseismic modeling IV Some assumptions We work in the seismic frequency range, then Re(η/κ(ω)) η/κ and 1 ω Im(η/κ(ω)) g = 1.5 ρ f T φ, T being the tortuosity factor so that the low-frequency Biot s equations are recovered. The electroseismic coupling coefficient L is assumed to be frequency independent, L = φ T F (s) = F (f ) =, and ωε/σ 1 ε κ f ζ (1 2 d η Λ ), We consider lossy media using Liu s model. Electro-filtration feedback negligible; this decouples the EM fields from the poroviscoelastic response. (This makes calculations easier) EOST, March 12th, 213

7 Scheme of the Finite Element Procedure Create a partition of the domain (elements). Transform original equations into a "weak form". Choose appropriate polynomial functions to approximate the solution in each element, (dofs). Transform the weak form into a linear sistem, and solve it. ( unknowns) EOST, March 12th, 213

8 Single horizontal layer 7 m 4 m 4 m Medium 1 Medium 2 (layer) σ (S/m).1.1 φ ( ).2.33 Ks (Pa) vp (m/s) vs (m/s) ρs (kg/m 3 ) k (m 2 ) L Q ( ) 9 9 ρf (kg/m 3 ) 1 1 η (kg/(m s)).1.1 Kf (Pa) Sf ( ) 1 1 EOST, March 12th, 213

9 Single horizontal layer SHTE-mode a b t=.3 s b t=.4 s c a b t=.1 s c d t=.2 s EOST, March 12th, 213

10 Single horizontal layer Different layer widths, SHTE-mode 4e-1 3e-1 2e-1 4 m Acceleration [m/s^2] 5e-1 4e-1 3e-1 2e-1 1 m 1e-1-1e-1-2e-1-3e-1 1e-1-1e-1-2e-1-3e-1-4e-1-5e-1-4e-1-6e e-1 5 m 3e-1 2 m 4e-1 2e-1 2e-1 1e-1-2e-1-1e-1-4e-1-2e-1-6e-1-3e-1-8e-1-4e t[s] t[s] EOST, March 12th, 213

11 Single horizontal layer PSTVM-mode 1e-12 8e-13 Acceleration traces - X component [m/s 2 ] -7 m m 7 m 1e-11 8e-12 Acceleration traces - Z component [m/s 2 ] -7 m m 7 m 6e-13 6e-12 4e-13 4e-12 2e-13 2e-12-2e-12-2e-13-4e-12-4e-13-6e-12-6e-13-8e-12-8e t [s] -1e t [s] EOST, March 12th, 213

12 Single horizontal layer PSTVM-mode 2e e-14 Div and Curl of an acceleration trace SV Div Curl 1e-14 5e-15-5e-15-1e e-14-2e e-14 P t [s] EOST, March 12th, 213

13 Wedge First Layer Second layer Third layer Wedge σ c (S/m) φ ( ) Ks (Pa) m vp (m/s) vs (m/s) ρs (kg/m 3 ) m 2 m k (m 2 ) L m 65 m 4 m Q ( ) ρf (kg/m 3 ) η (kg/(m s)) Kf (Pa) Sf ( ) EOST, March 12th, 213

14 Surface gather x-component acceleration Traces 2 4 Traces a a time(s).2 b time(s).2 b.3 c.3 d.4.4 EOST, March 12th, 213

15 Surface gather z-component acceleration Traces 2 4 Traces time(s).2 a time(s).2 a b b.3 c EOST, March 12th, 213

16 Methane hydrates (GH)......form stable ice-like crystals in permafrost regions and beneath the ocean floor along continental margins. Ellis, 28...are considered as a potentially huge energy resource....have the highest energy density of any naturally occurring form of methane (about 16 times that of methane gas)...decrease the electrical conductivity of the medium. EOST, March 12th, 213

17 Composite Media We use an extended Biot theory for composite matrix rocks with non uniform porosity distributions. The solid matrix can be formed by mixtures of different mineral grains. A fraction of the GH (ice) is assumed to form a second matrix occupying the pore space, and the rest of it is assumed to cement the mineral grains. LettingV = (V c gh + V nc gh ) + V mg + V f, V p = V V mg, φ a = V p /V ; and C gh = V c gh /V gh,cementation coefficient, S gh = V gh /V p GH saturation, all (Biot) model parameters are obtained in terms of C gh, S gh, φ a, K j mg and µ j mg forming the solid matrix; and K gh, µ gh. EOST, March 12th, 213

18 The Model x z 48 m Permafrost 31 m 25 m 6 m Sandstone 1 Sandstone 2 21 m GH Saturated Slab Permafrost Sandstone Slab (Sgh =.1) Slab (Sgh =.8) φ Vp m/s Vs m/s σ S/m L A/(Pa m) EOST, March 12th, 213

19 SHTE-mode Acceleration surface gather Surface detectors locations (m) Surface detectors locations (m) A.4 A Time (s) Time (s).6.6 B.8.8 C Without hydrate With hydrate EOST, March 12th, 213

20 SHTE-mode Acceleration well gather 8 8 F I 6 C D 6 J E C H Depth (m) A 4 Depth (m) 4 A B B G Time (s) Without hydrate Time (s) With hydrate EOST, March 12th, 213

21 SHTE-mode Acceleration surface trace for S gh =.1 and S gh =.8 5e-9 4e-9 3e-9 2e-9 1e-9-1e-9-2e-9-3e-9-4e-9 Solid Acceleration (m/s 2 ) S gh =.1 S gh =.8-5e t (s) 8e-1 6e-1 4e-1 2e-1-2e-1-4e-1-6e-1 Solid Acceleration (m/s 2 ) S gh =.1 S gh =.8-8e t (s) EOST, March 12th, 213

22 PSVTM-mode Acceleration (x-component) well gather 8 8 E F 6 C D 6 C D G Depth (m) 4 A Depth (m) 4 A H 2 B 2 B Time (s) Without hydrate Time (s) With hydrate EOST, March 12th, 213

23 PSVTM-mode Acceleration well traces for for S gh =.1 and S gh =.8 X-component solid acceleration (m/s 2 ) 6e-13 Well Trace #61 4e-13 2e-13-2e-13-4e-13-6e-13 S gh =. S gh =.1 S gh =.8-8e t (s) Z-component solid acceleration (m/s 2 ) 2.5e-12 S gh =. 2e-12 S gh =.1 S gh =.8 1.5e-12 1e-12 5e-13-5e-13-1e e-12 Well Trace #61-2e t (s) EOST, March 12th, 213

24 CO 2 storage monitoring The Model 1 mts (a) z Geophones (b) Air x Electromagnetic source 7mts 1 mts 4 mts 4 mts Seal layer Reservoir Homogeneous Soil EOST, March 12th, 213

25 CO 2 storage monitoring PSVTM mode, acceleration traces 4e-15 3e-15 x-component of acceleration traces [m/s 2 ] % 15 % 55 % 95 % 1.5e-14 1e-14 z-component of acceleration traces [m/s 2 ] % 15 % 55 % 95 % 2e-15 1e-15 5e-15-1e-15-5e-15-2e-15-3e-15-1e-14-4e t [s] -1.5e t [s] EOST, March 12th, 213

26 CO 2 storage monitoring PSVTM mode, acceleration traces 4e-15 3e-15 x-component of acceleration traces [m/s 2 ] (a) (b) 1.2e-14 1e-14 8e-15 z-component of acceleration traces [m/s 2 ] (a) (b) 2e-15 6e-15 4e-15 1e-15 2e-15-2e-15-1e-15-4e-15-2e-15-6e-15-8e-15-3e t [s] -1e t [s] EOST, March 12th, 213

27 Summary We have developed a numerical tool to simulate electroseismic (and seismoelectric) phenomena. It was observed that the response is sensitive to changes in fluid conductivities (mixtures of gas an brine). We have shown that methane hydrates can be detected by means of electroseismics on land in permafrost regions. We have observed that the seismic response is sensitive to methane hydrate concentration Preliminar results indicate that it could be very interesting to consider electroseismics/ seismoelectrics as a monitoring tools for CO 2 storage sites. Heaps of work ahead! EOST, March 12th, 213