Transcript Slides

(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
June 2007 28 - 29 Drilling cost effectiveness and feasibility of
high-temperature drilling - Reykjavik, Iceland, Workshop4
Stimulation of reservoir and
microseismicity Summary of the Ittingen
workshop
HUENGES1, Ernst., Kohl² Thomas
1GeoForschungsZentrum Potsdam (GFZ),
²GEOWATT
Cooper Basin AU
Groß Schönebeck
Soultz-sous Forets
Landau
Unterhaching
productive
hydrothermal
Basaltic rocks IS
Commercial
Potentially
commercial
HotDry
Rock
Suitable for reservoir
enhancement*
High
natural permeability
Zero
*Mechanical, chemical, or thermal stimulation, directional drilling etc.
mod.from USGS
How can we enhance the energy recovery?
(i)
Mechanical stimulation
From dry rocks: Creating
an artificial heat exchanger
at depth using hydraulicfracturing techniques;
operating with surface
water for heat extraction,
e.g. Soultz-sous-Forêts
(ii) 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 (massive hydraulic injection):
pore pressure
Shear fracturing
Tensile fracture
still a matter of
trial and error
generation of microseismicity and
transmissivity increases
Torsten Tischner
European HotDryRock Project Soultz-sous-Forêts
relocation seismic events GPK2, 2000
Asanuma et al.
2002
Tohoku University,
Japan
MTC Project
European HotDryRock Project Soultz-sous-Forêts
relocation seismic events GPK2, 2000
Asanuma et al.
2002
Tohoku University,
Japan
MTC Project
Hydraulic fracturing – Visualization of the process
• Processes in hydraulic fracturing
Wellbore
Injection
Leakoff
Friction
Elastic opening
Fracture Propagation
Rock Strength
Pressure support
of fracture walls
Stress Intensity
Factor
Peter Fokker
Proppant fracs
150 mm
successful propped hydraulic fracture requires:
• knowledge about the in-situ stresses,
• the reservoir permeability,
• the elastic parameters, and
• the fracture propagation criteria.
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.
Thermal (low T) stimulation
Gudni Axelsson
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
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.
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
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)
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 CO2sequestration
• the exchange with nuclear industry /hydrogeology
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!
Thank you for attention
Further informations:
http://conferences-engine.brgm.fr/getFile.py/access?resId=0&materialId=14&confId=3