This document summarizes a laboratory study on radial jet drilling of laterals for geothermal applications. The study aims to determine if there is damage around a jetted borehole and how jet drilling performs under stressed rock conditions. Computed tomography scans and tests on jetted rock samples show little damage around the borehole for the tested rock type. Further true-triaxial jetting tests are planned with higher nozzle pressures, various stress orientations and magnitudes, and different rock types to further understand the process.

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A laboratory study on
the drilling of laterals by
jetting
Geothermal Get Together
12 July 2018
Dr. Richard Bakker
The SURE project has received funding from the European Union’s Horizon 2020
research and innovation programmeunder grant agreement No 654662

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Radial Jet Drilling
• Jet-drilling of laterals
– Enhancing flow paths
– Less water usage compared to hydraulic
fracturing
– Less risk of induced seismicity
• Research questions
– Is there a damage zone around the jetted
hole?
– How does jet-drilling perform when rocks
under (true-triaxial) stress?

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Radial Jet Drilling
S. Hahn, personal communication.

4. 4
Is there damage around a jetted
borehole?
Bakker & Barnhoorn, in review
Journ. Rock Mech Rock Eng

5. 5
CT scan results
Bakker & Barnhoorn, in review

6. 6
Calculated porosity per slice
Bakker & Barnhoorn, in review

7. 7
Acoustic wave speeds
Bakker & Barnhoorn, in review

8. 8
Tensile strength tests
Bakker & Barnhoorn, in review

9. 9
Uniaxial compression tests
Bakker & Barnhoorn, in review

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True-triaxial testing
• 3 orthogonal
loading directions
• Max. 350 tonnes
per direction
– ~ 39 MPa with
30x30 cm2 area
– equivalent load of
~400 Fiat 500’s

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Testing blocks with jetted holes
Bakker & Barnhoorn, in review

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Testing blocks with jetted holes
Bakker & Barnhoorn, in review

13. 13Bakker & Barnhoorn, in review

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Initial jetting test
Jetted hole
trajectory?
25 MPa
5 MPa300 -350 mm

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Jetted laterals
310 mm

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Story so far
• No significant damage around the jetted
borehole
– .. for this rock type
• More jetting tests in the true triaxial
apparatus planned..
– Higher jetting nozzle pressure (300 bar
compared to 140 bar before)
– Various stress orientations
– Various stress magnitudes
– Various rock types (sandstone & chalk)

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Thank you for your attention
r.r.bakker@tudelft.nl