Page 212 - Geothermal Energy Systems Exploration, Development, and Utilization

188 4 Enhancing Geothermal Reservoirs

Figure 4.7 Wellhead Groß Sch¨onebeck designed for 600 bar wellhead pressure.

to protect the tubings in the upper part of the well. This can be solved by installation
of a frac string specially configured for the frac treatment. The installation of a blow
out preventer is a highly recommended option if any gas indication or pressurized
reservoir conditions are concerned.
A stimulation pump is a trailer-mounted fracturing service pumping unit de-
signed for high-horsepower applications. The pump delivers fracturing fluids to
the well at high pressure and rate. It is equipped with a remote panel allowing
control of the fracturing job away. The panel allows gear selection, throttle control,
and emergency shutdown to be performed.
A centrifugal pump will be required to feed water from the frac tanks and
filtration system to the high pressure pumps.
Frac tanks are used to store water before stimulation treatment. If these tanks
are internally coated or are manufactured from stainless steel, they tanks give the
option to pre-filter the water and store it in advance of the treatment.
The blender is a fracturing service blender which is capable of blending and
pumping fracturing slurry. It controls the solid/liquid ratio at design values
throughout the entire treatment. A computer-controlled integral gate meters the
amount of proppant added to the slurry.
Liquid additive systems are used for accurate metering of fracturing additives.
Typically, each unit consists of stainless steel tanks, connected to positive displace-
ment pumps and micromotion flow meters. This allows to accurately pump the
required chemicals.
For storage and delivery of the proppant to the blenders, stimulation sand silos
are used. Gravity silos are equipped with hydraulically controlled discharge outlets
at the bottom of the tanks. These are connected to the sleeves which assure
proppant delivery straight in the blender. The silo feeds sand to the blender during
fracturing operations and serves as a sand storage facility at the wellsite.
The main concern in filtration is to prevent reservoir damage. Many contaminants
can plug off the reservoir /production zones during completion and water injection.
This filter system protects the reservoir from contaminants, including bacteria,
scale, clay, rust, and so on.