Design of drilling robot for geothermal energy production final(1)

Design of drilling robot for
Geothermal Energy Production
C. Balaji Krishna kumar,
Assistant professor,
Department of Mechanical Engineering,
Saveetha University, Thandalam, Tamilnadu, India.
Abstract
We need electricity for transport by electric vehicles, household utility,
industrial manufacturing, food processing, and many other requirements. The
electricity requirements of the world including India are increasing at alarming rate
and the power demand has been running ahead of supply. It is also now widely
recognized that the fossil fuels (i.e., coal, petroleum and natural gas) and other
conventional resources, presently being used for generation of electrical energy, may
not be either sufficient or suitable to keep pace with ever increasing demand of the
electrical energy of the world. Also generation of electrical power by coal based
steam power plant or nuclear power plants causes pollution, which is likely to be
more acute in future due to large generating capacity on one side and greater
awareness of the people in this respect.
The recent severe energy crisis has forced the world to develop new and alternative
methods of power generation, which could not be adopted so far due to various
reasons. The magneto-hydro-dynamic (MHD) power generation is one of the
examples of a new unique method of power generation. The other non-conventional
methods of power generation may be such as solar cells, fuel cells, thermo-electric

generator, thermionic converter, solar power generation, wind power generation, geo-
thermal energy generation, tidal power generation etc.
Geothermal energy is so important that it can only build other renewable sources of
energy for the future need. This paper paves the way to drill from 5 to 20 kilometers
using mechanisms and robotics. The given mechanism is highly cost effective and
easy to drill. This paper combines both rotary and percussion type of drilling.
Keywords: cost effective Geothermal energy technology, pollution control, Global warming
control, robotic drill, mechanism for drilling geothermal energy, rotary and percussion
drilling.
Introduction
Heat energy continuously flows to the Earth’s surface from its interior, where
central temperatures of about 6 000°C exist. The predominant source of the Earth’s
heat is the gradual decay of long-lived radioactive isotopes (40K, 232Th, 235U and
238U). The outward transfer of heat occurs by means of conductive heat flow and
convective flows of molten mantle beneath the Earth’s crust. This results in a mean
heat flux at the Earth’s surface of 80kW/km2
approximately. This heat flux, however,
is not distributed uniformly over the Earth’s surface; rather, it is concentrated along
active tectonic plate boundaries where volcanic activity transports high temperature
molten material to the near surface.
Although volcanoes erupt small portions of this molten rock that feeds them, the vast
majority of it remains at depths of 5 to 20 km, where it is in the form of liquid or
solidifying magma bodies that release heat to surrounding rock. Under the right
conditions, water can penetrate into these hot rock zones, resulting in the formation of

high temperature geothermal systems containing hot water, water and steam, or steam,
at depths of 500 m to >3,000 m.
Global warming can be prevented if we bring geothermal energy at the
earliest. Pollution control from vehicles and industries must be brought to control and
deforestation must be controlled. Otherwise in about three centuries from now ice age
will start and worst difficulty will arise for mankind. So, Geothermal energy must be
brought as quickly as possible to prevent ice age forever. Geothermal, Oil and gas
well drilling technology use Tricone bits and diamond coring bits. Water bore well
drills use flat rock drills. All these drill bits uses drilling at slow speeds.
Radial arc drill, thermal spalling, are other drills that can drill but it cannot be
used for deep drilling due to weight of the pipe. In this paper, these drills are replaced
by tapered solid drill bit which provides faster and energy efficient drilling.
In the present geothermal drilling technology, drilling after 20kms can create
seismicity since the load due the drill pipes acting at this depth is of the order of
25000 T. Tension and compression the drill pipe also causes breakage with loss of
investment.
Similar to Water well 1 metre hole is drilled. Cementing and grouting has to
be done similar to oil and gas wells.
A mechanism to retain the drill is provided. This mechanism is safe and will
not kinder the tectonic plate movements or seismicity. At 5-25 kms depth, vibrations
produced due to the drill will be less than Secondary velocity of 3 m/s. Diamond
embedded tapered drills is very effective in drilling hot temperature rocks.
Global warming control and pollution control can be achieved by geothermal
energy production.

Material and Method
Composite drill pipes are being used for reducing the weight of the drill pipe
in Geothermal, oil and gas drilling. Though the cost increases by ten times there is 37
% decrease in drill pipe weight.
A robotic drilling system can be used for drilling upto 5 kms in geothermal zones.
First 3 to 5 kms can be drilled by robotic system beyond 5 kms to reach 15-25 kms in
other than geothermal zones the pneumatic drilling system can be used. The robotic
system consists of a drill connected to a heavy duty motor which is fixed to drilled
circumferential hole pin. So, it is rotatable. Always a fixed point or support is
essential for rotation or drilling. The circumferential hole pin acts as a fixed point
where the heavy duty motor is fixed and it rotates the drill. The Geothermal zones has
to be identified and Temperature profile of the area under various depths has to be
identified. It is more accurate if we can know each layer of rock underneath. In this
system of drilling it is possible to visualize the area of drilling with the help of
thermal vision, thermally insulated camera and light fixed inside the drill.
Tracks are made by the support of drilled side holes.
The rate of pressure increase with depth is called the pressure gradient, and depends
on the density of the overlying rock. The pressure gradient is linear in the crust,
mantle and inner core because they are (mostly) composed of solids, but non-linear in
the outer core because it is a liquid. A good approximation of the rate of pressure
increase with depth is: 30 MPa/km in the crust and 35 MPa/km in the mantle.
The rate of temperature variation with depth is called the geothermal gradient and
varies greatly with location and depth. Temperature increases at a rate of
approximately 20o
C/km in the upper crust (first 10 km) but then the rate decreases to

only approximately 0.3o
C/km below 200km due to the homogenizing effect of mantle
convection.
Include drill stem type of drilling for more than 5-10-20 kms of depth.
First drilling to 5-7kms with 100 C where ever possible and using isobutene as
working fluid then drilling using drill stem method to reach 10-25 kms.
Figure 1. Piston and Cylinder arrangement
Compressed air for double
acting cylinders which enables
to move the cylinders up and
down along the splined shaft.
Latch on the drill
pipe for the
compressed
Air cylinderset.
2 m
Suction
of
debris

Figure. 2 Robotic drilling system
Thrust producing
rockets to carry
the debris to the
surface
High
capacity
Motor for
rotating the
drill
Rockets for
bringing the
entire
systems to
the surface
Control
system
Composite
material
Drill
embedded
with
diamonds
Circumferential
drilling system
Holder
support
Contractible
and
extendable
rods
Robot to collect
and fix the
holder support

Figure3. Wire holding system
Thermally
insulated
electrical wires
hanging on the
circumferential
hole
Camera
tracks
Robot
for
extending
the wires
from one
point to
other
Motor to
drivealong the
tracks between
the
circumferentially
drilled hole
lights

Figure 4. Circumferential drilling using gear drive mechanism
Using gear drive mechanism, shown in Fig 3. , the drilling is carried out along
thecircumference of the hole. This mechanism is supported and powered by the drill
pipe and this provides a sturdy operation. After drilling, the circumferential drill bit
has to be retained between the rocks after penetration to maximum depth. After
drilling the first part, the second part of the circumferential drill is brought by the
movement of the ladder along the tracks from the surface or by the rocket system and
it is connected to the first part. Usually a drill bit is three or four parts connected
Robot
for
engaging
gears
Journal
Bearing-
block -100
Kgs
Piston/cylinder Piston/cylinder
Rack and Pinion
M
es
he
d
H
el
ic
al
G
ea
r
B
E
A
R
I
N
G
Piston/cylinder

together to hold the weight of the drill pipe. The drill bit of diameter 1 m drills to a
depth of 25 m and the ladder moves the first set of drill weight holding rods to the
next 25 m after drilling circumferentially.
Figure. 5. Schematic layout of the container weight reducing system.
Pressure increases with depth in the earth due to the increasing mass of the rock
overburden.Computing the pressure as a function of depth in a homogeneous crust is a
straightforwardcalculation. In SI units, pressure (Pascals) is the force (Newtons) per
unit area (meters2
) suchthat1 Pa = 1 N/m2
.
You may also see pressure written as barsor atmospheres with
1 bar = 1 x 105
Pa = 0.9872 atm.
Considerthe pressure beneath a one meter cube of granite (density = 2.8x103
kg/m3
).
The force appliedby the 2.8x103
kg of this cube to the rocks beneath it is given by
force = mass x acceleration = (2.8x103
) (9.8 m/s2
) = 2.7x104
N.
where (9.8 m/s2
) = g, the acceleration of gravity at the surface of the earth.
This force isdistributed across the 1 m2
area of the base of the cube, the pressure
beneath the cube ispressure = 2.7x104
N
1 m2
= 2.7x104
Pa.
Ø 1m
Ø0.7m
Ø 0.75m
Ø 0.85 m
Ø 0.03m
Grouting and Cementing
Aluminium Or Mild steel
Container with holders
plugs

If another cube is placed on top of the first one, the pressure under the two cubes will
be 5.4x104
Pa. As more cubes are stacked, the pressure at the base rises at the rate of
2.7x104
Pa/m = 2.7x107
Pa/km = 27 MPa/km = 270 bars/kmwhere MPa (=106
Pa)
stands for megapascals. Alternatively, this pressure distribution may be
expressed as3.7 km/kbar = 37 km/GPawhere GPa (=109
Pa) stands for gigapascals.
For a uniform crustal density of 2.8x103
kg/m3
. Higher densities will yield higher
pressuregradients. The geostatic gradient changes with depth as the density increases.
F = m a
= 2.8 x 103
x 9.8 m/s2
= 2.7 x 104
N
Ultimate Strength of mild steel 8 x 104
T/ m2
or 60,000 psi
Pressure distribution
3.7 km / k bar
= 37 km/GPa
10000 psi
Density of mildsteel 7.8 g/cm3
Ultimate tensile strength of mild steel is 400 Mpa, at geothermal zones 30 Mpa/km
pressure acts. So, drilling can be done easily at 5kms. 100 Mpa at 10 kms deep and
200 Mpa at 20 kms acts under the sea depths. So, the Robot will withstand the
pressure and drilling can be done.
The total weight of the drill is 4 T/m3
and the density of mild steel is 8 x 103
T/m3
.
Hencecircumferential drilled rodis capable of withstanding weight of the robot
equipment.

Figure 6. Driving mechanism
The system consists of springing type suspension mechanism made of pneumatic
cylinders to handle hammering action. When load is applied on the drill pipe
pneumatically the set of cylinders holding the drill pipes and drill bit will oscillate up
and down evenly like a spring and the total weight of the drill pipe is shared by the
circumferential holes. Hammering is mainly needed to break especially granite rocks
by impact loads.
The drilling mechanism comprises of series of set of compressed air cylinder with the
bearing and compressed air receiver set up is moved to the next latch hole after
detachment.
Tomotor
To
motor
Holders
Controlled
by Robot
Helical
worm type
gear
Note: Driving mechanism
from the surface to be
supported without
hindering the gripper and
working mechanism.

Figure 7. Compressed air assembly movement system.
Compressed air for double
acting cylinders which
enables to move the
cylinders up and down
along the splined shaft.
Latch on the drill
pipe for the
compressed
Air cylinder set.
2 m
Suction of debris
Multiple
(one inside
another
flexible)
metal
tubing for
sending air
for the
movement
of the
cylinder
set.

Figure 8. Compressed air cylinder mechanism
Roller Bearing
Length of
spring ½ L1
Length of spring
½ L 1
Length of
spring L1
Ladders carrying
equipments driven
by sequence of
gears from the top
and using steam
turbines /cylinders
along tracks.
The set of spring
with compressed
air cylinder moves
down for each
depth and moves
up similarly to
remove the setup
after drilling and
completion
Hole 3: Compressed air
for double acting
cylinders
Hole 1 :
Suction of
debris after
drilling
Hole 2: Supply of coolant
Note: Pressurised air
pipes provide air to the
pneumatic pressured
screw type cylinders.
Suction of the debris
after drilling is done
through the drill stem
through the hole inside
after drilling to certain
depth. The weight of
the whole system is
calculated and reduced
by providing more
number of
circumferential drills.

Figure 9. Spring based accumulator with drill pipe
The cylinders are controlled by valves during pressurising on one side for the rod
end to elongate and depressurising on the other side. Once the assembly is attached to
the next hole the compressed air cylinder is adjusted to take loads. After moving one
assembly next set of compressed air cylinder assembly is moved up or down based on
whether it is drilling or removal after drilling. When force is applied from the top the
drill stem moves down and the set of compressed air cylinder assemblies compress to
approximately half the maximum extension. So, drilling is completed to certain depth
and the set of cylinder assemblies moves inward and cylinders extend to maximum.
This operation is repeated to reach the required depth.
In geo thermal drilling the weight of the drill with the series of drill pipes is of
the order of thousands of tons. Hence, slow drilling process with very high torque
values is used for drilling. The Drill weight reducing system consists of series of
pneumatic cylinders to produce hammering action by adjustment of cylinder. These
Pneumatic accumulator
for saving space best suited for
the
drilling process
Piston and cylinder
spring
Drill pipe

pneumatic cylinders are controlled accurately so the lifting of the entire drill pipe is
uniform and it breaks the rocks mainly granite with even rotary and impact loads.
Figure 10. Drill weight reducing system in front view
Figure 11. Schematic layout of the drill weight reducing system in top view.
The pneumatic cylinders are 4 metres long and are placed at right angles at 90
degrees with 2 metre spacing between each set of cylinders. The pneumatic cylinders
can be of 5-20 metres long even, this will reduce the number of circumferential holes
Springs or
steam jackets
with holding
pins
Bearing
Locks
Ladder on
tracks
Weight
holding
rods
Suction
through
Drill pipe
Ladder with
equipments
Piston and
cylinder for
moving in and out
of the rings of the
circumferential
drillPneumatic
Cylinders that provide
the action
of springs

required to be drilled. The circumferential hole should be drilled deeper and with
larger hole size based on the total weight of the cylinder. The weight holding rod
consists of two parts; one part is fixed to one end of the pneumatic cylinder and other
end moves into the circumferentially drilled ring by means of a cylinder.
Figure 12. Detailed view of weight holding rod with cylinder.
After drilling 15 metres deep with the main drill and then the 4
circumferential holes are drilled at right angles to each other, the containers each of 2
metres length is fixed to the cylinder and extended for 2 metres and fixed to the
circumferential holes.
After moving the first set of cylinder to the circumferential hole the cylinder is
allowed to take up the load of the drill pipe by pressurising pneumatically. Next, the
cylinder adjacent at 90 degrees is fixed with the next 2 metre container and moved to
the next set of circumferential holes. Then the whole of the cylinder set is moved by
detaching from the drill pipe and after the cylinder set is moved the piston is retracted
inside the cylinder.
First 4 set of containers and the ladders are hardened in order to support the
circumferential drilling or Composite containers can be used.
The suspension or hammering system uses pneumatic cylinders and
Drill weight reducing rods. The cylinders are always placed at half its total extension
Cylinder
Rod holder ring

i.e. 2 metres for hammering action during drilling. As the load is exerted from the
surface each cylinder compresses the air at a gradual pressure.
Using the gear drive mechanism, the drilling is carried out along the
circumference of the hole.
This mechanism is supported and powered by the drill pipe and this provides
a sturdy operation. After drilling, the circumferential drill bit has to be retained
between the rocks after penetration to maximum depth. After drilling the first part, the
second part of the circumferential drill is brought by the movement of the ladder
along the tracks from the surface and it is connected to the first part by the
circumferential drilling mechanism. A circumferential drill is of solid drill divided
into parts connected by means of threading in order to penetrate deeply. If the drilling
hole size is of 2 metres and the circumferential depth required is 4 metres then each
part of the drill set should be of 30 centimetres length. Depth required is calculated
based on the rock area in order to hold the weight of the drill pipe. After drilling to a
certain depth (25 m) the first set of circumferential drills is placed and weight
reducing rods are inserted into the ring of the circumferential drill bits. Again the 1 m
diameter drill bit drills to 25 m and the ladder moves the first set of drill weight
holding rods to the next 25 m after drilling circumferentially. The pneumatic jackets
compress and elongate based on air flow adjustment of compressed air in pneumatic
cylinders through pipes. The flow of pressurised air is controlled by flow adjustment
valves. This produces hammering action and drilling is completed to further depths.
After drilling to 10 kilometres the temperature and pressure of the system
increases along with the depth. This pressure is blocked by the weight of the solid
tapered drill bit and blow out is prevented by the circumferentially drilled weight
reducing system.

For each depth a set of container is moved forward. In this mechanism, drill pipe
is fixed with bearings and suspended over with cylinders. A set consisting of mud fall
blocking pipe, drill weight reducing rods, and the drill pipe is inserted together for a
calculated depth each time. Where, holding plug is detachable. So, for every increase
in calculated drill depth, holes are created at an angle along the circumference of the
mud fall blocking container or barrel for a calculated distance into the drilled hole
through rock drill bits. This is done in order to prevent entire weight of the drill pipe,
of length 15 kilo metres or more, to act on the drill bit.
Three set of containers are fixed to the ladder system which are suspended by
cylinders to the gears based on the weight against free fall and the ladder can move on
tracks through the entire depth.
The ratchet and pawl mechanism, pawl with springs prevent the ladder from freefall
and holds it on to the tracks.
The pawl releases the gear only if the spring force is exceeded by the engine.
While the ladder is moving upwards it moves freely.
Figure 13. Ratchet and Pawl mechanism for ladder movement along tracks.
During circumferential drilling the ladder is fixed to the stops on the container.
Engine
Ladder
Gears on the ladder
fixed to the engine.
Gears with pawl and
springs to hold the pawl
against free fall of the
ladder.

After drilling to certain depth using the 1 metre drill, holes are drilled to the
circumference and barrels are moved by the help of the drill pipe and cylinders. Then
the first set of barrel is moved by using the cylinders. This makes the all other set of
cylinders below to compress to a certain level as the additional weight of the drill pipe
acts, due to the release of the one set of cylinders. Similarly when the bottom most set
of cylinders are released the load of the entire drill with additional cylinders drill pipe
weight is shared by the all other sets of pneumatic cylinder. The container is first
fixed to the ladder and locks are detached for the first container to move freely. So,
the first container advances into the depth and is made to seat on the already drilled
circumferential drill pins. Each circumferential drill pin is drilled for a depth to carry
the drill pipe weight, set of cylinder weight and the container weight with a safety
margin. Similarly the next set of containers is moved in to the depths. For 10 kilo
metre, 5000 barrels made of composites are required each of two metres length. After
drilling to certain depth each container is moved and placed on the circumferential
drilled weight holder pins.
The lead part of the drill is made sharp with a diamond tip and the body has
steps of various diameters. Carbide buttons with diamonds are brazed along with
High-speed steel drill body. The drill can be two fluted or three fluted. Three fluted
drill are more advantageous than two fluted. Coolant for the drilling operation is
provided through a separate hose. Suction of debris after drilling is done through the
drill pipe. After a certain depth the debris comes out and is sucked through the drill
pipe.
Cementing and grouting is not essential but can be used if necessary after
drilling certain depth.

Geothermal zones have a temperature starting between 500°C to 1000°C.
Generally, even 20 - 25 kilo metres depth can produce high geothermal zones even
without reservoirs. Cryogenic technology will be required to cool the drill and its
mechanisms are at very high temperatures and pressures, beyond 25 kilo metres.
Thrust and torque
The thrust ball bearings are used for carrying thrust loads exclusively and at
speeds up to 2000 rpm. At high speeds, centrifugal forces cause the balls to be forced
out of races. Therefore at high speeds it is recommended that angular contact ball
bearings should be used in place of thrust ball
bearings.
Figure 14. Container lift mechanism and Cryogenic cooling
Seal or cover against
high pressure
As the container moves down
the seal moves up then comes
back down
Space for cryogenic cooling of
the drill

Figure 15. Container movement
Figure 16. tightly sealed container movement against high pressure
Moving high pressure
seal container
Seal 1
Seal 2

Figure 17. Vessel seal against high pressure
Figure 18. seismic effect
A hole drilled does not disturb the sides or underneath so no seismic effect
will be formed.
Vibration of the drill produces a hammering effect
that is not too heavy to produce seismicity. This is because only 50-70 T
hammers rather that a weight of 10000T.
Maximum
50-70T
Drill
weight
Seal against high
pressure
Shutter against high
pressure

Figure 19.arrangement for joining of the drill pipes using nut
Figure 20. Shutter mechanism for inserting the drill against high pressure
25 m
Lever for opening and
closing of external door
Bearing with seal
Rack and pinion arrangement for
up down movement of the door.
5 mm thick Mild steel plate
Drill bit
Nut
For tightening pipes
Bearing
Pipe 2
Pipe 1
Torque resistant and
air tight seal
Insert Protrusion
between pipe 1 and 2

So, for 20 kilo metres weight of 5000 T, the number of circumferential drills required
is 200, 000 at each set at 4 metres gap.
Results and discussion
In today’s world clean energy without enhancing global warming is essential and
vital. If oil and gas and coal reserves are used and exhausted by 2050 to run the
present 1000 crores or 100 billion population by developing all other the energy forms
such as solar energy, wind energy, and other renewable energy resources. For the
future development Geothermal Energy is essential and vital.
It is now economical to drill the Earth’s crust and bring out geothermal energy with
the help of robotic mechanism designed. When drilling into supercritical conditions,
many problems may occur due to severe conditions related to increasing well depth
and rising temperatures and pressures, so an advanced drilling technology is needed.
The technical gain from deep drilling and research could have a global impact on
geothermal utilization and is a challenging project worthy of international
collaboration. It provides more jobs for the future generation with an expanding
population.
Earth’s crust is not moving, it is stationary, so rarely techtonic or blow out causes
earth quakes. The earth quake is mostly due to series of metallic pipes weight order of
10000 tons acting on the techtonic plates.
References
[1] Dr. William C. Maurer, Novel drilling techniques, 15-105 pp.
[2] Drilling data handbook and practices manual, Oil and Natural Gas corporation of
India pp.
[3] Gene culver, Geo heat center, Klamath Falls, Oregon, “Drilling and well
construction”, pp 129-164.

Design of drilling robot for geothermal energy production final(1)

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