Page 174 - Geothermal Energy Systems Exploration, Development, and Utilization

150 3 Drilling into Geothermal Reservoirs

(b)

(a)
Figure 3.21 (a) Process of sidetrack drilling by
setting a whipstock acting as a wedge (From
www.glossary.oilfield.slb.com.). (b) Staged sidetrack
mill as part of a whipstock. (From GtGrSk4/05.)

• Add a safety margin for the weight loss when hanging casing string into slips.
• Check whether the casing design allows application of additional tensile load.
• Check whether the casing design of the anchor string allows the application of
the total load of all casing/tubing strings and the wellhead.

3.7.1.3 Liner in Pay Zone (Slotted/Predrilled) or Barefoot Completion
Depending on the borehole stability in the pay zone it has to be decided whether
a slotted or predrilled liner should be run to prevent the borehole from collapsing
during production/reinjection or whether the borehole can be used without a liner
(= ‘‘barefoot’’). It should be noticed that a barefoot completion offers the lowest
flow resistance (pressure drop) and is therefore the best to lower total energy
consumption during operational phase (production/injection).

3.7.2
Wellheads, Valves and so on

A wellhead is the top end of a borehole. Besides the purpose to allow flow
into or out of the well – depending on whether the well is used for injection
or production – the wellhead it is also equipped with valves which can be used
to shut in the borehole, for example, for safety reasons. The wellhead normally