Page 168 - Geothermal Energy Systems Exploration, Development, and Utilization

144 3 Drilling into Geothermal Reservoirs
3.6.2
Site Preparation and Infrastructure

3.6.2.1 General
Once a drill site has been selected and surveyed, the necessary lines for electric
power supply, water supply (if necessary by drilling new groundwater wells), and
waste disposal need to be organized. A drill site can only be adequately prepared,
if the drill rig and its dimension are predefined since the rig fundament needs to
achieve the statics. If necessary, the site will be cleared and leveled. For practical
and safety reasons, a drill site should be separated in three areas: (i) internal area
with drill rig, engines, and machinery; (ii) external area for necessary traffic of
machines and transport; and (iii) peripheral area for parking, storage space for
casings, tubings, and further equipment.

3.6.2.2 Excavating and Trenching
The scale and duration of excavating and trenching are minor and site-specific.
On most drill sites, a below-ground-level cellar may be excavated. This pit provides
additional space between the rig floor and the wellhead to accommodate the
installation of BOPs, rat holes, and so on. It also collects drainage water and other
fluids for disposal. A reserve pit lined with plastic to prevent soil contamination
and settling pits may be excavated and used for water or mud discharges.

3.6.2.3 Environmental Impact (Noise, Pollution Prevention)
Attenuation of noise of the rig engines may be necessary in urbanized areas or in
24 hour operation in populated areas. Also, special care may have to be taken for
noise protection against noises generated by handling the drillstring, for example,
during roundtrips. Attenuation may be given by installation of sound insulating
walls and covered drill rig engines as the rig assembly allows covering. Pollution
of groundwater and soil needs to be avoided by appropriate sealed fundament and
sealed excavations.

3.6.3
Drilling Operations

The normal drilling operation starts after the site construction is finished with the
move and rig-up of the drill rig.
The next work steps are
• mix drill mud;
• run in hole drill bit and DCs;
• start drilling, add drillpipe as needed;
• pull out drill bit if it is worn out and/or if section depth is reached;
• perform geophysical and technical logging as needed;
• run in hole casing (or liner) to section depth;
• cement the annulus between casing/liner and open hole;
• nipple up and pressure test BOP stack;