Deep drilling - Risks and challenges

with examples from the German Molasse Basin

April 2009 Pumping Test Dürrnhaar Summer 2008

Molasse Basin

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Molasse Basin

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The geothermal conditions in the South of the Molasse Basin can roughly be summarized as follows: Rising temperatures in the Malm due to increasing depth of burial of the Malm. This must be countered with greater drilling depths. Tendentially decreasing geothermal gradients towards the edge of the Alps. Besides that, local temperature anomalies exist.

Geothermal Background German Molasse Basin

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Quelle: GGA-Temperaturkarten im Bayerischen Geothermieatlas, Bay. Geol. Landesamt, Bay. StWIVT 2004

Temperature cross section4000 m below ground

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Hydrogeology of Molasse Basin („bath tube filled with limestone, sandstone, sand and clay“)

Mechanismen of Deep Groundwater systems

Geological cross section Munich Area N - S

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Tertiary “Molasse”

CretaceousJurassic Malm Aquifer

82°C

80°C

99°C

117°C

130°C

The average value of the geothermal gradient in the Munich area is approximately 3.2°C/100 m. In the direction toward the edge of the Alps the gradient can generally assumed to be lower than, for example, in the Munich area.

www.geovol.de

February 2009

Geothermics: Permit situation and potentential of geothermal use

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Short “claim”History

2002 6 “Claims” in southern Bavaria

2001-2004 4 Drilling projects in Bavaria

2006 90 “Claims” in southern Bavaria (!)

2008-2009 9 Drilling projects (!!)

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Differences of geothermal systems

- Petrophysical Systems Hot Dry Rock Enhanced Geothermal System or Hot Fractured Rock (HDR or EGS or HFR) Use of storaged thermal potential, Thermal transport has to be realized by injection of artificial fluid (preferably water) -> European Projects are in pilot state

- Hydrothermal Systems with high Temperature -> Vapor Systems (T > ca. 170°C) classic worldwide geothermal use -> USA, Iceland, Italy, New Zealand)

- Hydrothermal Systems with low Temperature) Hot water Systems hot (T > 100°C), warm (T ca. 40 - 100°C), low temperature (T ca. 25 - 40°C), preferably from deep ground water systems in sedimentary basins (Molasse, basin parisiennne or Hungarian basin, etc.)

Basics on deep geothermal systems

Aquifer types in the Bavarian Molasse Basin

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The Malm carbonates are considered as a Fracture- (and in parts: Karst-) Aquifer

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Soultz-sous-Forêts

Hot Dry Rock Pilot Project

- Bad Urach (Spa) / Southern Germany Project was interrupted because of financial problems

- Soultz-sous-Forêt (bei Straßburg)hydraulic pump and reinjection tests were finished. Project is being realized (EU financed project)

- Baselhydraulic fracturing induced earth quake project was interrupted for more detailed seismic investigations

Hot Dry Rock or Geothermal Enhanced Geothermal Systems -

Geological Risk Issues

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Quelle: Bayerischer Geothermieatlas, Bay. Geol. Landesamt, Bay. StWIVT 2004

a. Identify and comment on any key technical risk issues associated with this project in terms of:

•Achieving the required production flows rates from the proposed development plan•Possibility of cool reinjection returns to production wells • Possible chemical issues during production – e.g. chemical scaling in wells and pumps, corrosion etc.

b. Extent to which any project risks identified in the above have been considered in the project development plan

Geothermal Doublets Munich Riem and

Pullach i. Isartal

(both projects are represented in the internet also)

Project Examples

Concept Design of the GeothermalDoublets Riem and Pullach i. Isartal:

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During the concept design and detailed design stages, the geothermal projects for the trade-fair town Riem and for the town of Pullach i. Isartal underwent comparable project phases that included feasibility studies, reprocessing of existing 2D seismic data of the hydrocarbon industry, and a concluding risk analysis, in which the results of the feasibility study were examined after a detailed analysis of the seismic data.

After an EU-wide prequalification and invitation to tender, as well as intense bidder negotiations, a day-rate drilling contract was signed in each case based on the geological and drilling concept design, with the drilling company assuming the role of general contractor. Major criteria for the decision – in addition to the profitability – included the drilling company's many years of experience with deep drilling operations in the Northern Alpine Molasse zone, as well as the selection and quality of the subcontractors and service companies. Both clients (Stadtwerke München GmbH and Innovative Energie für Pullach GmbH) were willing to accept the full responsibility, as is customary in the drilling industry, for any risk related to geological and drilling problems. Neither project was insured against drilling risks or exploration risks (!)

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Drilling Project cost simulation

The drilling time schedule should be simulated.

A drilling time versus depth diagram is usefully to decide with drilling pad is the most reasonable.

The basic simulation must – if possible - use information's from other wells or deep drilling projects in the area.

-> Most detailed Feasibility Studies has to be done !!!

Interpretation of the seismic profiles

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Drilling concept (double-doublet) (3D-GIS Modell)

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Drill pad design has to be optimized on fault structure targets

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Riem: RAG-RIG W9general contractor RAG AG (Austria)

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• IDECO SBS

• Hook Load: 160 to

• Rotary Drive

• Mud pumps: 580 / 724 kW

• Energy supply: gas-electric

• Quick moving of heavy work-

over rig in two days

Drilling rate: Riem Thermal 1 (3.275 m ET)

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Contract by day-rate !

40 days final depth !

estimated drilling time curve by contractor

real drilling time

Pullach: ITAG- Rig 23general contractor ITAG GmbH und Co. KG

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• Hook load: 445 to

• Top Drive

• Mud pumps: 2 x 1250 kW

• Energy supply: -> electric!

• Well cluster site -> skidding

system (moving from well 1

to 2 in 4-6 hours!)

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Pullach: Drilling and casing design

Pullach Th 1 / 1a

Pullach Th 2

Side track Th 1a concept

6.1/8 = 156 mmdrilling diameter

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Depth versus drilling time Pullach Thermal 2 (4.120 m ET)

Bohrvertrag auf Day-Rate !

62,5 Tage ET !

Requirements: Geothermal Power

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The geothermal energy use in both projects is for district heating concept only!

Required for the profitability:

min. 6 MW

min. 6.3 MW

min. 9 MW /actual 11 MW (!)

min. 7 MW

Riem

Pullach

Geothermal output:

Basic works for a higher success rate

Evaluation of deep wells in the surrounding area

Detailed evaluation of seismic data (including reprocessing)

Drilling concept designs with deviation wells and directional drilling (deepening, options for side-tracks with horizontal deviation up to 70°)

Drilling rigs with sufficient capacities

Drilling contracts which allow flexible responses to the geological situation (day-rates)

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Costs by day-rate contracts for deviated wells

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Riem 1+2 (2003) meters 6.500 m 817 EUR / m(heavy workover rig )

Pullach 1+2 (2005)(stationary rig) meters 8.786 m 1.024 EUR / m

Sauerlach 1+2+3 (2007-2009) meters >16.000 m > 2.000 EUR / m

Dürrnhaar 1+2 (2007-2009) meters > 11.000 m > 2.000 EUR / m

Difference: Riem & Pullach to Sauerlach & Dürrnhaar-Vertical Depth > 4.000 m (!)- final drilling diameter 8.1/2” to 6.1/8” (big hole completion !)

Geological and technical Problems on big hole very deep geothermal wells !

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1) Problems with borehole failures and borehole breakouts in the lower part of Tertiary-Sediments (may be induced by anisotropically prestressed rocks) .In the case of Project Sauerlach several side- tracks had to be drilled to reach the target

2) Problems with heavy drilling fluid losses in cretaceous sediments

3) Problems with casing stability (collapse) caused by very high production temperatures and very long drilling time (significant decrease of casing wall thickness)

For all these problems we finally founded solutions but the final-drilling costs were high! (drilling costs were doubled!)

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Deep well Sauerlach Th 3 > 5.000 m (MD) Time versus depth

Costs by day-rate contracts for deviated wells

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Riem 1+2 (2003) meters 6.500 m 817 EUR / m(heavy workover rig )

Pullach 1+2 (2005)(stationary rig) meters 8.786 m 1.024 EUR / m

Sauerlach 1+2+3 (2007-2009) meters >16.000 m > 2.000 EUR / m

Dürrnhaar 1+2 (2007-2009) meters > 11.000 m > 2.000 EUR / m

Difference: Riem & Pullach to Sauerlach & Dürrnhaar-Vertical Depth > 4.000 m (!)- final drilling diameter 8.1/2” to 6.1/8” (big hole completion !)

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Occlude cutting drain for drilling fluids from the rig floor

Damaged centralizer from logging Tool (after running in borehole)

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Drilling bits heavily damaged by abrasive sandstone!

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Drilling bits totally damaged by abrasive sandstone!

Drill pipe twisted!

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Pins of drill pipes damaged -> BHA was lost

Overshot for Fishing Job was twisted

„Nobody is perfect”or Deep Drillingneeds positive thinking!

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Nobody is perfect!