PowerPointPrsentation

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Geothermal research well in a deep sedimentary
reservoir Huenges Ernst, Moeck Inga, Saadat Ali,
Brandt Wulf, Schulz Axel, Holl Heinz-Gerd, Bruhn
David, Zimmermann Günter, Blöcher Guido, Schulte
Thomas and Wohlgemuth Lothar funded by
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Focus of Geothermal Research
Identification and characterization of
geological structures suitable for geothermal
utilization Focus on sedimentary water
bearing rocks (hydrothermal reser- voirs) in
the North German Basin, representative for large
sedimen- tary basins in Europe
Development of stimulation techniques to enhance
the fluid productivity of reservoirs (Enhanced
Geothermal Systems) and to guarantee a
longterm extraction of geothermal energy
(reservoir- optimized stimulation concepts)
Development of process technology in converting
the earths heat into electrical energy with
the focus on efficient low temperature
solutions
FOCUS
Provision of site-independent customized concepts
Utilization of geothermal energy in an
environmentally friendly and sustainable way
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In situ geothermal laboratory Gross Schoenebeck

• Status
• 2 research boreholes, 4.3 km deep, temperatures
  150 C reaching a reservoir. Both wells used to
  develop and test stimulation concepts to enhance
  mass-flow rate
• Ongoing October 2007test the well and
  installation of a doublet system,
• demonstration of sustainable production with
  longterm circulation
• Perspectives Demonstration of geothermal power
  production in the North German Basin

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Geology
4300m TVD
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Completion of the geothermal laboratory
Drilling challenges (2006/2007) large
diameter balanced drilling into the reservoir
directional well
Directional drilling concept of the 2nd well
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Drilling problems

• significantly larger diameter
• Insufficient pumping capacity
• improper bit selection 16 PDC-bit after
  drilling of 7m unexpectedly abrasive
  sandstone

ROP less than expected
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Drilling problems
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Drilling problems
Total fluid loss during cementation of casing
16x13 3/8 (density 1450 kg/m³). To prevent
thermally induced casing damage (during
production) gt squeeze cementation from top -
down
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Drilling problems

• 9 5/8 liner collapsed after reduction of the mud
  density from 2000 kg/m³ to 1060 kg/m³. Causes not
  yet clear
• Design according to the rules with an
  overburden pressure gradient of 2,3
• Casing material certified quality
• Anisotropic stress due to well inclination of
  about 20 in connection with
• anhydrite content of the salt?

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Remedy for the collapse

• Replacement of the collapsed 9 5/8 liner by a
  7x7 5/8 liner after sidetracking
• Repeated attempts (4 times) to set the mechanical
  anchor of the whipstock required the modification
  of the anchor for a reliable operation in mud
  with 40 baryte content

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Drilling problems

• HC - gas with H2S - content below the 7 5/8
  casing shoe (within fissured Zechsteinkalk) with
  a pressure gradient exceeding 1,2.

• Adjusted drilling concept (minimum damage
  potential!)
• not more a nearly balanced drilling
• permanent threat of differential sticking with a
  mud density of 12001160 kg/m³
• marble flour based mud but small fluid losses
  within the coarse sandstones

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Reservoir engineering
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Reservoir engineering
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Reservoir engineering
EGS laboratory Groß Schönebeck treated intervals
in well 4/05 (August/Sept.2007)
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Conclusions

• from our experiences in a case study of a deep
  sedimentary reservoir
• Drilling
• Reopening of an abondonned former gas exploration
  well an option
• Drilling (2.well) large diameter feasible (23)
  but challenging especially in clay dominated
  layers
• Directional drilling a standard operation
• Need of variable mud concepts to react to
  unforseens (formation damage, breakout, H2S-
  inflows,..)
• Several hydraulic fracture treatments
• gt how to engineer an EGS reservoir by hydraulic
  fracturing in sandstone and volcanic rocks
• Concept based on parallel fracs perpendicular to
  the connecting line of both well bottom sections
  using the transmissibility within the
  formationgt reservoir performance (not shown
  fracture mapping, geochemistry)
• Groß Schönebeck site since 2001, with gt 10 MW
  thermal power _at_ 150 C expected after drilling
  and enhancing the second borehole (testing is
  ongoing!)
• Groß Schönebeck research test site to develop
  deep sedimentary geothermal reservoirs

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Thank you for your attention