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Mechanical Stimulation and implications from microseismicity - - PowerPoint PPT Presentation

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ENGINE ENhanced Geothermal Innovative Network for Europe Workshop 3 "Stimulation of reservoir and microseismicity" Mechanical Stimulation and implications from microseismicity Thomas Kohl, GEOWATT AG Clment Baujard, GEOWATT AG

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29 June 2006 ENGINE - Kartause Ittingen

Mechanical Stimulation and implications from microseismicity

Thomas Kohl, GEOWATT AG Clément Baujard, GEOWATT AG Zürich, Switzerland

ENGINE – ENhanced Geothermal Innovative Network for Europe Workshop 3 "Stimulation of reservoir and microseismicity"

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29 June 2006 ENGINE - Kartause Ittingen

Mechanical (hydraulic) stimulation

  • Faulting (= shear fracturing): shearing of pre-existing fractures, Soultz

(mechanism is stress field dependant)

  • Jointing (= hydrofrac, tensile fracturing, extensional fracturing): creation
  • f new fractures, common in petroleum industry
  • Jacking: aperture enlargement of pre-existing fractures, Rosemanowes

and Le Mayet-de-Montagne with proppant and gel injections

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29 June 2006 ENGINE - Kartause Ittingen

Hydraulic Stimulation

major parameter for failure in an EGS reservoir is the stress regime, i.e. relative vertical / horizontal stress

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29 June 2006 ENGINE - Kartause Ittingen

Mechanical (hydraulic) Stimulation

Faulting (shear fracturing)

Increase of pore pressure Slip of pre-existing mechanical discontinuities Generation of larger apertures / or new faults

Mohr (-Coulomb) - Criterion Microseismicity

Prediction of Magnitudes (Gutenberg-Richter) Identification of large structures (e.g. multiplet analysis) Identification of hydraulic diffusivity

Stimulation of multiple fracture sets, mostly in crystalline rock

( )

n

c σ τ

  • Φ

+ = tan

σh σH

Evans

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29 June 2006 ENGINE - Kartause Ittingen

Mechanical (hydraulic) Stimulation

Jointing (tensile fracture)

Develops perpendicular to least principal stress

Criterion Applied mostly in sedimentary rocks Creation of single, far extending fractures

p f f

P S P S P ⋅ + + > + > α σ σ

min min

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29 June 2006 ENGINE - Kartause Ittingen

Analysis of Microseismic Density from Stimulations in Soultz

  • GPK2 Stimulation (July 2000): 14'080 events
  • GPK3 Stimulation (July 2003): 21'600 events
  • GPK4 Stimulation (September 2004): 5'753 events
  • GPK4 Stimulation (February 2005): 2'966 events
  • GPK4 1st Step rate test (February 2005): 183 events
  • GPK4 Acidization test (March 2005): 304 events
  • GPK4 2nd Step rate test (March 2005): 256 events
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29 June 2006 ENGINE - Kartause Ittingen

Analysis of Microseismic Density from Stimulations

Total events Calculated cube volumes: 50x50x50m3

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29 June 2006 ENGINE - Kartause Ittingen

Analysis of Microseismic Density from Stimulations

Calculated low-density structure N96p64W.

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29 June 2006 ENGINE - Kartause Ittingen

Analysis of Microseismic Density from Stimulations

Comparison of GPK4 Stimulations: September 2004 February 2005

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29 June 2006 ENGINE - Kartause Ittingen

Analysis of Microseismic Density from Stimulations

Comparison of GPK2/3/4 Stimulations Compare at 100m cube:

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29 June 2006 ENGINE - Kartause Ittingen

Conclusion on possible hydraulic impact of low-seismic zone

High conductive zone (draining fluid into a far field fault zone and thus prevents any pressure increase)

"Fingering" of microseismic density indicates flow into this zone No increase of the density of microseismic events once zone has reached and injection continues Weak hydraulic connection between GPK3 and GPK4 Tracer diffusion into this "storage zone" can explain the small tracer recovery Next to the intersection with GPK4 depth, high fluid-losses were encountered during drilling

High impedance zone (extreme low natural fracturization = possible no-flow boundary)

Orientation nearly perpendicular to SH; Long transients during GPK4 shut-in Weak hydraulic connection between GPK3 and GPK4 Hardly no tracer recovery between GPK3 and GPK4 High seismic density between GPK4 and aseismic zone

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29 June 2006 ENGINE - Kartause Ittingen

Conclusion on possible hydraulic impact of low-seismic zone

individual observations are non-unique (I.e. tracer breakthrough) ⇒ ambivalent characterization. Although orientation does not coincide with N-S pattern, such faults necessarily exist on Horst structures High impedance needs extreme low fracturization that is hardly to imagine for the general permeability pattern ⇒ aseismic zone corresponds to a subvertical structure that is well linked to N-S striking drainage systems ⇒ Due to its orientation, we can expect a low compliance for normal stress variations and especially little shearing.

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29 June 2006 ENGINE - Kartause Ittingen

Complex tectonic regimes

Interplay of different tectonic mechanisms can lead to faulting ~parallel to Sh:

  • rotational bulk strain
  • Pull-apart
  • en-echelon structures
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29 June 2006 ENGINE - Kartause Ittingen

Conclusion

The hydraulic re-stimulation of GPK4 includes the risk

  • f low efficiency and of higher seismicity.

A proper hydraulic characterization of the aseismic zone between GPK3 / GPK4 is necessary for a successful GPK4 re-stimulation. Microseismicity favours structures parallel to SH

However perpendicular structures may exist Visible only as low seismic activity

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29 June 2006 ENGINE - Kartause Ittingen

Modeling Tool HEX-S: Prognosis GPK4 stimulation 04SEP13

Forecast Measurement

  • 5500
  • 5000
  • 4500

Depth

500

Easting

  • 2000
  • 1500
  • 1000

Northing

X Y Z

  • 6000
  • 5000
  • 4000
  • 3000

x3

  • 1000

1000

x1

  • 2000
  • 1000

1000

x2

time [s] ∆Pdh [MPa] Qin Omega

100000 200000 300000 5 10 15 20 10 20 30 40 50 60 70 80 90 100

Ref.pressure 45.0 MPa

time [s] ∆Pdh [Pa]

100000 200000 5E+06 1E+07 1.5E+07 2E+07 2.5E+07

IImodl : 6.9-7.4 IImodl : 9.7-10.7

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29 June 2006 ENGINE - Kartause Ittingen

Modeling Tool HEX-S: Stimulation Model

Forecast model did not include aseismic zone New fault model of the 5km reservoir at Soultz

deterministic fractures intersecting the GPK3 and GPK4 borehole faults derived from the seismic distribution using the density analysis aseismic zone with high hydraulic conductivity, i.e. flow injected to GPK4 will be drained through this zone into a nearby N-S extending Soultz fault.

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29 June 2006 ENGINE - Kartause Ittingen

Modeling Tool HEX-S: New Stimulation Model

Determination of fault planes from microseismic distribution

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29 June 2006 ENGINE - Kartause Ittingen

Modeling Tool HEX-S: New Stimulation Model

Three Scenarios:

  • 1. Single injection in GPK4 with

30 l/s during 3 days and increase to 45 l/s (i.e. injection scenario from Sep. 2004)

  • 2. Dual injection in GPK3 / GPK4

each with 30 l/s during 3 days and increase to 45 l/s

  • 3. Doubling injection in GPK4

with 60 l/s during 3 days and increase to 90 l/s (i.e. doubled flow scenario 1)

Northing [m]

000

  • 2000
  • 1000

1000 2000

ction GPK3 & GPK4: 2 x 30 l/s ⏐ 26 Apr 2006 ⏐

Northing [m]

000

  • 2000
  • 1000

1000 2000

ction GPK4: 60 l/s ⏐ 26 Apr 2006 ⏐

Northing [m]

000

  • 2000
  • 1000

1000 2000

1.2E+07 1.1E+07 1E+07 9E+06 8E+06 7E+06 6E+06 5E+06 4E+06 3E+06 2E+06 1E+06

ection 30 l/s ⏐ 26 Apr 2006 ⏐

GPK4 GPK3 GPK4 GPK3 GPK4 GPK3

Not yet fully calibrated!

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29 June 2006 ENGINE - Kartause Ittingen

Modeling Tool HEX-S: New Stimulation Model

Three Scenarios:

  • first injection step at

t=10'000 s and 1 day second injection step at t=1 day after step change pressure history in GPK4

GPK4 GPK3

Northing [m] Pressure [Pa]

  • 2000
  • 1500
  • 1000
  • 500

500 1000 2E+06 4E+06 6E+06 8E+06 1E+07 1.2E+07 1.4E+07 1.6E+07

Injection GPK4: 45 l s-1 Injection GPK3 & GPK4: 2 x 45 l s-1 Injection GPK4: 90 l s-1

1 day injection 45 l/s ⏐ 26 Apr 2006 ⏐

time [s] Pressure [Pa]

50000 100000 150000 2E+06 4E+06 6E+06 8E+06 1E+07 1.2E+07 1.4E+07 1.6E+07

Injection GPK4 30/45 l s-1 Injection GPK3 & GPK4: 30/45 l s-1 Injection GPK4: 60/90 l s-1

Pressure History GPK4 ⏐ 26 Apr 2006 ⏐

GPK4 GPK3

Northing [m] Pressure [Pa]

  • 2000
  • 1500
  • 1000
  • 500

500 1000 2E+06 4E+06 6E+06 8E+06 1E+07 1.2E+07 1.4E+07 1.6E+07

Injection GPK4: 30 l s-1 Injection GPK4: 30 l s-1 Injection GPK3 & GPK4: 2 x 30 l s-1 Injection GPK3 & GPK4: 2 x 30 l s-1 Injection GPK4: 60 l s-1 Injection GPK4: 60 l s-1

10'000sec / 1 day injection: 30 l/s ⏐ 26 Apr 2006 ⏐

10'000 sec 1 day

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29 June 2006 ENGINE - Kartause Ittingen

Recommendations for Mechanical Stimulation

Modeling indicates

Transmissivities are created mostly in the vicinity of the boreholes Little success in far field stimulation

Short-term injections (1-2 days):

prevents pressure build up in secondary flow zones (pore pressure) limits the size of the affected area. Successive short-term injections more efficient than long re-stimulations Dual injection would yield shorter transients in matrix / larger volumes.

When reaching maximum pressure:

avoiding long-term shut-in. venting of boreholes as fast as possible

Chemical stimulation not considered.

several successive chemical / mechanical stimulation they are complementary in nature:

  • acidization with HCl rather affects the nearest borehole vicinity
  • mechanical stimulation will influence the natural fracture network
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29 June 2006 ENGINE - Kartause Ittingen

Chemical stimulation

Acidization is used for

removal of skin damage from drilling operations increase of formation permeability in undamaged wells.

The injection of acids is performed

at modest flow rate (below pressures for mechanical stimulation) 1) preflush, usually with hydrochloric acid 2) mainflush usually with a hydrochloric – hydrofluoric acid mixture. 3) postflush/overflush usually with soft HCl acid solutions or with KCl, NH4Cl solutions and freshwater.

Improvement of the well conditions can be generally

  • bserved (largely varying success).

André & Vuataz