Drilling, stimulation and reservoir assessment for EGS and UGR projects

Thomas Kohl, GEOWATT AG

Sverrir Thorhallsson, ISOR

European EGS/UGR Projects

• Several European research projects in past 30 years • Widely different geological conditions • New projects in construction

Two ENGINE workshops "Best Practices" are planned• Economic development of resources

improving output of wells by stimulation / drilling lowering the cost of drilling.

• Reservoir assessment and available geoscientific information.

• Recent technological advances in these areas will be examined

Countries with conv. production (large/small)Failed / abandoned EGS/UGR projectsRunning EGS/UGR projectsPlanned EGS/UGR projects

Development from HDR to EGS Concept

Typical System Requirements:

Example: Production of 35 MWth (3.5 MWel) over 30 yr duration: Heat exchange area ~1.7 km2

Maximum temperature decrease after 30 yr: 20% Flowrate 45 l/s Flow impedance 0.2 GPa per m3/s

Rosemanowes Fenton Hill Soultz

Soultz EGS System

Northern Upper Rhine Graben Temperature distribution in 500m

EPS1

GPK1

GPK2

Temperature distribution in Rhine Graben

GGA, Hannover

Improve output of wells

How to improve the yield of wells?• Larger diameter wells• Underbalanced drilling• Well stimulation• Use of water only for drilling• Deep pumps

DrillingNew Equipment

Effectiveness in Drilling

Jarðboranir hf.

Top Drive and Automatic Pipe handling

Jarðboranir hf.

Modern Geothermal Rig

Stimulation Techniques

Chemical stimulation• Corrosion• Effect of concentration

Mechanical (hydraulic) Stimulation• Proppant vs water frac• Predicability• Optimizing test duriation

Stimulation by Explosives

Thermal Stimulation

Workshop "Stimulation of Reservoir and Induced Microseismicity"

29. June – 30. June 2006

Kartause Ittingen, Warth, Switzerland

1. July 2006: Excursion "Grimsel Test Site"

Registration deadline: 25. March 2006flyers (draft) available

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 stimul

ation)1) preflush, usually with hydrochloric acid2) mainflush usually with a hydrochloric – hydrofluoric acid mix

ture. 3) postflush/overflush usually with soft HCl acid solutions or wi

th KCl, NH4Cl solutions and freshwater.

Improvement of the well conditions can be generally observed (largely varying success).

André & Vuataz

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

nc tan

h

H

Evans

Mechanical (hydraulic) Stimulation

Jointing (tensile fracture)• Develops perpendicular to least principal stress

Criterion

Applied mostly in sedimentary rocks

Creation of single, far extending fractures

pf

f

PSP

SP

min

min

Stimulation of GPK4 (Sep04): Microseismic Development

E.E.I.G.

Top South West

Located seismic events

Calculated Shearing Events

Critère de rupture [MPa] :

Modeling TechniquesFRACAS

C. Baujard/ D. Bruel

Modeling TechniquesHEX-S: Prognosis of stimulation

Forecast Measurement

C. Baujard

-5500

-5000

-4500

De

pth

0

500

-2000-1500-1000

Northing

XY

Z

-6000

-5000

-4000

-3000

-2000

x3

-100001000

x1-2000-100001000

x2

XY

Z

stim0047.datstim0048.datstim0049.datstim0050.datstim0051.datstim0052.datstim0053.datstim0054.datstim0055.datstim0056.datstim0057.datstim0058.datstim0059.datstim0060.datstim0061.datstim0062.datstim0063.dat

time [s]

Pd

h[M

Pa

]

Qin

Om

eg

a

100000 200000 3000000

5

10

15

20

0

10

20

30

40

50

60

70

80

90

100

Ref.pressure45.0 MPa

time [s]

Pdh

[Pa]

Flo

wra

te[l/

s]

0 100000 200000 3000000

5E+06

1E+07

1.5E+07

2E+07

2.5E+07

0

10

20

30

40

50

60

70

80

90

100

Pdh B1

Qinj [l/s]

Pdh C2

Pdh C3

GPK4 Stimulation Sep.2004; Modell b1/cx

IImodl : 6.9-7.4 IImodl : 9.7-10.7

Conclusion

Drilling, stimulation and reservoir assessment are most important for EGS and UGR concepts

Underbalanced drilling may help to maintain natural permeability

Experience exists on• EGS in Europe• on stimulation techniques

Hydraulic post-stimulation behaviour has not always improved

The complex interplay between microseismicity and fluid pathways can be forecasted