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(Expertise on) Drilling, stimulation and reservoir assessment

(Expertise on) Drilling, stimulation and reservoir assessment. WP4 Sverrir Thorhallsson WP7 Ernst Huenges. June 2006 29 Jun - 01 Jul Stimulation of reservoir and induced microseismicity - Zurich, Switzerland, Workshop3.

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(Expertise on) Drilling, stimulation and reservoir assessment

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  1. (Expertise on)Drilling, stimulation and reservoir assessment WP4 Sverrir Thorhallsson WP7 Ernst Huenges June 2006 29 Jun - 01 JulStimulation of reservoir and induced microseismicity - Zurich, Switzerland, Workshop3 June 2007 28 - 29Drilling cost effectiveness and feasibility of high-temperature drilling - Reykjavik, Iceland, Workshop4

  2. Stimulation of reservoir and microseismicity - Summary of the Ittingen workshop HUENGES1, Ernst., Kohl² Thomas 1GeoForschungsZentrum Potsdam (GFZ), ²GEOWATT

  3. Potentially commercial Commercial Soultz-sous Forets Groß Schönebeck Cooper Basin AU Unterhaching Basaltic rocks IS Landau Suitable for reservoir enhancement* *Mechanical, chemical, or thermal stimulation, directional drilling etc. productive hydrothermal HotDry Rock High Zero natural permeability mod.from USGS

  4. How can we enhance the energy recovery? • From dry rocks: Creating an artificial heat exchanger at depth using hydraulic- fracturing techniques; operating with surface water for heat extraction, e.g. Soultz-sous-Forêts • From water-bearing rocks: Creating artificial pathways at depth to enhance the thermal water flow, operating with downhole pumps installed in a production well + reinjection well, e.g. Groß Schönebeck Mechanical stimulation

  5. Mechanical stimulation (massive hydraulic injection): pore pressure Shear fracturing Tensile fracture still a matter of trial and error generation of microseismicity and transmissivity increases Torsten Tischner

  6. European HotDryRock Project Soultz-sous-Forêts relocation seismic events GPK2, 2000 Asanuma et al. 2002 Tohoku University, Japan MTC Project

  7. European HotDryRock Project Soultz-sous-Forêts relocation seismic events GPK2, 2000 Asanuma et al. 2002 Tohoku University, Japan MTC Project

  8. Hydraulic fracturing – Visualization of the process • Processes in hydraulic fracturing Wellbore Leakoff Injection Friction Fracture Propagation Rock Strength Stress Intensity Factor Elastic opening Pressure support of fracture walls Peter Fokker

  9. Proppant fracs • successful propped hydraulic fracture requires: • knowledge about the in-situ stresses, • the reservoir permeability, • the elastic parameters, and • the fracture propagation criteria. 150 mm

  10. Geochemical stimulation • Acid treatments successfully applied to enhance geothermal production rates to commercial levels • developed to address similar problems in oil and gas production wells but applicability to a hot and fractured reservoir less well known • temperatures dependence of the acid-rock reaction rate • to clean (pre-existing) fractures by dissolving filling materials (secondary minerals or drilling mud) and mobilizing them for an efficient removal by flow transport. E.g. fractures partially filled with secondary carbonates (calcite and dolomite): • dissolve these carbonates and enhance the productivity around the well with various amounts of hydrochloric acid.

  11. Thermal (low T) stimulation Gudni Axelsson

  12. Thermal stimulation • cracking through thermal shocking (Low T) • by intermittent cold water injection, with periods of thermal recovery in-between injection periods (High T) • one of the most common methods used for high-temperature well stimulation in Iceland Gudni Axelsson

  13. Lessons learned (1) Understanding Many parameters play a role in the failure mechanism that is expected: • Fluid pressure development in the reservoirs, that depends on: • injection rate, time, and length • the setup of the test in the well • fluid type (water, heavy brine, gel of various viscosity, presence of proppants) • fluid temperature reservoir • Stress field, that is different for each EGS site • Rock and fractures parameters, like cohesion and Mohr angle, may highly influence results obtained, and could be modified by the use of proppant agents or acid treatments • Shearing represents the relaxation of the natural shear stresses within the rock mass triggered by the weakening of the fracture by the elevated fluid pressure. • The pore pressure increase required to initiate shear failure on favourably oriented fractures is often very small. • Earth's crust is close to failure (critically stressed). Permeability/porosity creation is done by the natural stresses.

  14. Lessons learned (2) To improve the basics it is recommended: • to focus on understanding stimulation and to work on the predictability of stimulation • to extend the knowledge about stress, artificial fractures, structures, fabrics (fracture propagation) • to focus on understanding self propping • to take proppant crushing into account • to visualise stimulation in different geological environments • to investigate scale dependence of fracture propagation • and the validation of acidification treatments

  15. Lessons learned (3) The needs are: • Extended experiences with 1:1 stimulation tests in boreholes • Experimentally modelling of ongoing processes in laboratories • Long-term circulation tests • Developing modelling tools (microseismicity) • and technical tools (seismic anisotropy) • Reliable monitoring tools (temperature, pressure, chemistry) • to go again to shallow borehole experiments • Geology 3D (impact of geology on success of EGS/HDR)

  16. Lessons learned (4) Review HC-Stimulation and EGS-development and others implicate: • More exchange hydrocarbon industry with geothermal industry • to extend the application of gel injection • to take proppant crashing into account • to consider the combination of geothermal experiments and CO2-sequestration • the exchange with nuclear industry /hydrogeology

  17. Lessons learned (5) Public acceptance • Geothermal energy as one of the future energy sources for base load power and heat provision is almost accepted. • Exploring (explosion seismics), accessing (drilling into) and engineering (stimulation) the reservoir needs to be explained to the public to hold the acceptance on a high level. • Especially high rate stimulation recognisable seismological events must be prepared in a reliable publication management ensuring that every potential affected person is reached. • In cases of violation of set thresholds the procedure most be stopped by the geothermal developer. This is much better than being stopped be local authorities!

  18. Thank you for attention Further informations: http://conferences-engine.brgm.fr/getFile.py/access?resId=0&materialId=14&confId=3

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