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 projects Running EGS/UGR projects Planned EGS/UGR projects

Development from HDR to EGS Concept Typical System Requirements: Example: Production of 35 MW th (  3.5 MW el ) over 30 yr duration:  Heat exchange area ~1.7 km 2  Maximum temperature decrease after 30 yr: 20%  Flowrate 45 l/s  Flow impedance 0.2 GPa per m 3 /s RosemanowesFenton 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

Drilling New 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 2006 flyers (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 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, NH 4 Cl 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 hh 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

Stimulation of GPK4 (Sep04): Microseismic Development E.E.I.G.

Top SouthWest Located seismic events Calculated Shearing Events Critère de rupture [MPa] : Modeling Techniques FRACAS C. Baujard/ D. Bruel

Modeling Techniques HEX-S: Prognosis of stimulation ForecastMeasurement C. Baujard

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