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 20oC/km in the upper crust (first 10 km) but then the rate decreases to

only approximately 0.3oC/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/m

2.

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/m

3).

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/s

2) = 2.7x10

4 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 = 2.7x10

4Pa.

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 = 2.7x10

7 Pa/km = 27 MPa/km = 270 bars/kmwhere MPa (=10

6 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/m

3. 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/s

2

= 2.7 x 104 N

Ultimate Strength of mild steel 8 x 104 T/ m

2 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 10

3 T/m

3.

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

drill Pneumatic

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.