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Table 1 Drill bit sizes and drilling methods used in DGE-1

From: Evaluation of the Lund deep geothermal exploration project in the Romeleåsen Fault Zone, South Sweden: a case study

Depth interval Drill bit size Drilling method
0–23 m 40″ (1016 mm) Auger drilling
23–165 m 26″ (660 mm) and 36″ (914 mm) hole opener Mud rotary drilling
165–1020 m 26″ (660 mm) Mud rotary drilling
1020–2044 m 17½″ (445 mm) Mud rotary drilling
2044–2119 m 12¼″ (311 mm) Mud rotary drilling
2119–2878 m 12¼″ (311 mm) Air rotary drilling
2878–2972 m 12¼″ (311 mm) Percussion drilling using air
2972–3365 m 12¼″ (311 mm) Air rotary drilling
3198a–3666 m 8½″ (244 mm) Mud rotary drilling using lightweight polymer mudb
3666–3675 m 8½″ (244 mm) Percussion drilling using mud
3675–3701.8 m 8½″ (244 mm) Mud rotary drilling using lightweight polymer mudb
  1. The crystalline basement was reached at 1946 m depth
  2. aDue to whipstock installation
  3. bMud weight between 1.02 and 1.05 g/cm3