Technical Manual for Drilling Works for Technical Support Plan for the Drillers in DDCA (2013)

Contents

1 INTRODUCTION

2 DRILLING TOOLS AND EQUIPMENT (TA COde 2)

2.1

SELECTION OF DRILLING BIT AND DRILLING METHOD (TA CODE 2-1)

2.2

ROTARY BITS (TA CODE 2-2)

2.3

DTH AND DTH BIT (TA CODE 2-3)

2.4

RIG ACCESSORY (TA CODE 2-4)

2.5

CASING TOOLS (TA CODE 2-5)

2.6

DRILLING EQUIPMENT (TA CODE 2-6)

2.7

DRILLING CALCULATION (TA CODE 2-7)

2.8

WEIGHT OF DRILLING TOOLS (TA CODE 2-8)

2.9

ROTARY BIT ROTATION SPEED AND WEGHT ON BIT (TA CODE 2-9)

2.10

DTH BIT ROTATION SPEED AND WEGHT ON BIT (TA CODE 2-10)

3 DRILLING CONTROL (TA Code 4)

3.1

MUD CONTROL (A CODE 4-1)

3.2

MUD PUMP OPERATION (TA CODE 4-2)

3.3 CASING FOR MUD DRILLING (TA CODE 4-3)

3.4 DRILLING OPERATION FOR MUD DRILLING (TA CODE 4-4)

3.5 BIT CONTROL AND REPARING FOR MUD DRILLING (TA CODE 4-5)

3.6 AIR CONTROL FOR DTH DRILLING (TA CODE 4-6)

3.7 AIR COMPRESSOR OPERATION (TA CODE 4-7)

3.8 CASING FOR DTH DRILLING (TA CODE 4-8)

3.9 DRILLING OPERATION FOR DTH DRILLING (TA CODE 4-9)

3.10 BIT CONTROL AND REPARING FOR DTH DRILLING (TA CODE 4-10)

4 BOREHOLE LOGGING (TA CODE 5)

4.1 BOEREHOLE LOGGING INSTRUMENTS (TA CODE 5-1)

4.2 INTERPRETATION OF BOREHOLE LOGGING RESULTS (TA CODE 5-2)

5 GRAVEL PACKING (TA COde 7)

5.1 DETERMINATION OF GRAVEL SIZE (TA CODE 7-1)

5.2

CALCULATION OF GRAVEL VOLUME (TA CODE 7-2)

5.3 GRAVEL PACKING (TA CODE 7-3)

6 WELL DEVELOPMENT (TA CODE 8)

6.1

WELL CLEANING AFTER DRILLING (TA CODE 8-1)

6.2

SINGLE TUBE METHOD AIR LIFTING (TA CODE 8-2)

6.3

DOUBLE-TUBE METHOD AIR LIFTING (TA CODE 8-3)

7 BACK-FILLING&SURFACE CEMENTING (TA CODE 9)

7.1

BACK-FILLING (TA CODE 9-1)

7.2 SURFACE CEMENTING (TA CODE 9-2)

2. Slurry poured into the borehole

8 PUMPING TEST (TA CODE 14)

8.1 PURPOSE AND METHODS OF PUMPING TEST (TA CODE 14-1)

8.2 PUMPING TEST EQUIPMENT (TA CODE 14-2)

8.3 SELECTION OF SUBMERSIBLE PUMP (TA CODE 14-3)

8.4

INTERPRETATION OF TEST RESULTS (TA CODE 14-4)

9 WATER QUALITY (TA CODE 15)

9.1 PURPOSE OF WATER QUALITY ANALYSIS (TA CODE 15-1)

9.2 ITEM OF WATER QUALITY ANALYIS (TA CODE 15-2)

Tables

Table 1 Identified Technical Areas Covering Drilling Works of DDCA

Table 2 Technical Area / Item Covered by Teaching Guidance and Manuals

Table 3 Drilling Performance of Drilling Methods for Type of Formation

Table 4 Selection of Bit for Rotary Cum DTH Drilling

Table 5 Connection of Rotary Bit

Table 6 Rig Accessories DDCA’s New Drilling Rig of 150 m Capacity

Table 7 Capacity of API Drill Pipe

Table 8 Capacity of API Drill Collar

Table 9 Identification of API Threads

Table 10 Size of API 5L-B Steel Pipes

Table 11 Size of JIS STPG Sch-40 Steel Pipes

Table 12 Size of JIS SGP Steel Pipes

Table 13 Size of BS Heavy Steel Pipes

Table 14 Size of uPVC Pipes

Table 15 Specifications of NP-700 Mud Pump

Table 16 Conversion Factors - Imperial to Metric

Table 17 Conversion Tables - Length and Area

Table 18 Conversion Tables - Velocity and Flow

Table 19 Conversion Tables - Imperial Gallons to Litres

Table 20 Conversion Tables - Litres to Imperial Gallons

Table 21 Conversion Tables - Acre-Feet to 1,000 Cubit Meters

Table 22

Conversion Tables - Cubic Yards to Cubic Meters

Table 23

Conversion Tables - Imperial Gallons Per Minute to Litres Per Second

Table 24

Conversion Tables - Pounds Per Square Inch to Kilo Pascals

Table 25

Conversion Tables - Horsepower to Kilowatts

Table 26

List of Necessary Tools for 12-1/4” and 8-1/2” Drilling

Table 27

Drill String Assembly for 12-1/4” x 30 m Drilling

Table 28

Drill String Assembly for 8-1/2” x 100 m Drilling

Table 29

Weight Calculation of Drill String Assembly for 12-1/4” x 30 m Drilling

Table 30

Weight Calculation of Drill String Assembly for 8-1/2” x 100 m Drilling

Table 31

Example of Bit Log Sheet

Table 32

Example of DTH Log Sheet

Table 33

Example of Cement Mixing Calculation

Table 34

Conversion Table of Discharge Rate for 90 Deg. Notch Tank

Table 35

Specifications of Submersible Pump SP17 (Grundfos)

Table 36

Water Quality Parameters and each Pollition Sources and Effects

Table 37

Values of WHO Guideline and TTS

Table 38

Frequency of Sampling for Rural Water Supply

Table 39

Frequency of Sampling for Urban Water Supply

Figures

Figure 1 Mechanism of DTH Drilling Method

Figure 2 Mechanism of Mud Rotary Drilling Method

Figure 3 Structure of Cable and Tool Drilling Machine

Figure 4 Structure of Tri-cone Tooth Bit

Figure 5 Structure of DTH

Figure 6 Structure of DTH Bits

Figure 7 Standard Drill Sttring Assembly

Figure 8 Specifications of Steel Casings and Drill Bits

Figure 9 Casing Lifting Tools

Figure 10 Structure of Truck-mounted Drilling Rig

Figure 11 Structure of Mud Pump

Figure 12 Duplex Mud Pump NP-700 (TONE)

Figure 13 Internal Structure of Mud Pump

Figure 14 Rotary Screw Air-Compressor PDSJ750S (21 m³/h, 21 bar)

Figure 15 Change of Drilling Speed by Operating Pressure of DTH

Figure 16

DDCA’s New Cargo Truck

Figure 17

Bit Penetration and Rotary Speed

Figure 18

Example of the Calculation of WOB

Figure 19

Standard Layout of Drilling Equipment on Site

Figure 20

Work Flow of Mud Drilling

Figure 21

DDCA’s Well Completion Form

Figure 22

DDCA’s Well Section Drawing Form

Figure 23

Example of the Casing Program for DTH Drilling Borehole

Figure 24

Work Flow of DTH Drilling

Figure 25

Work Procedure of Borehole Logging (Geologer 3030)

Figure 26

Example of Logging Result and Casing Program (Sedimentary Formation)

Figure 27

Example of Logging Result and Casing Program (Hard Rock Formation)

Figure 28

Example of Gravel Pack Design

Figure 29

Example of Sieve Analysis Sheet

Figure 30

Example of the Gravel Calculation

Figure 31

Installation of Gravel Pack

Figure 32

Measurement of Gravel Top

Figure 33

Installation of clay pellets

Figure 34

Development by Single-Tube Air-Lifting

Figure 35

Single Tube Air-Lifting Method

Figure 36

Double-Tube Air-Lifting Method

Figure 37 Government Specifications and Regulations Applicable to Water Well Drilling and

Installation Method

Figure 38 Work Procedure of Surface Cementing

Figure 39 Example of Results of Step Drawdown Tests (t-dwl curve)

Figure 40 Example of Results of Step Drawdown Tests (Q-s curve)

Figure 41 Example of Results of Step Drawdown Tests and Recovery Test (t-s curve)

Figure 42 Standard Setting of Pumping Test Instruments

Figure 43 Structure of Notch Tank

Figure 44 Example of Calculation of Pump Total Head (Discharge Rate 10 m³/h)

Figure 45 Pressure Loss Nomogram for Galvanized Steel Pipe

Figure 46 Pump Capacity Curve of SP17 Serieis (GRUNDFOS)

Figure 47 Example of Form of Summary of Pumping Test

Figure 48 DDCA’s Record Form of Constant Discharge Rate Test

Figure 49 DDCA’s Record Form of Recovery Test

Figure 50 Example of Results of Step Drawdown Test

Figure 51 DDCA’s Record Form of Recovery Test

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

1 INTRODUCTION

The baseline survey on DDCA’s drilling organization was conducted in the course of the Project,

for the purpose to reveal the current status of drilling works and the technical level of drillers in

DDCA. The results of the baseline survey were compiled in the Technical Support Plan for the

Drillers in DDCA (hereinafter referred to as “TSP”) which was formulated in January 2013. This

plan identified

15 technical areas which cover the drilling works of DDCA including eight

technical areas necessary to be enhanced and two new technical areas to be needed, as shown in

Table 1.

Table 1 Identified Technical Areas Covering Drilling Works of DDCA

New Areas

Areas to be

No.

Technical Area

All Areas

to be

Enhanced

Needed

Site Mobilization

✔

Drilling Tools and Equipment

✔

Drilling Drawbacks

✔

Drilling Control

✔

Borehole Logging

✔

Casing Program / Installation

✔

Gravel Packing

✔

Well Development

✔

Back-Filling & Surface Cementing

✔

Site Demobilization

✔

Well Investigation

✔

15 Water Quality Analysis

✔

This Technical Manual for Drilling Works was prepared according the TSP and covers eight

technical areas to be enhanced. This manual is expected to be utilized by the senior drillrs in

DDCA in order to acquire the necessary technical knowledge and the proper work procedures.

Furthermore, it forms a part of materials for the teaching guidance which is used for the technical

instruction to both private drillers and DDCA’s drillers. In the TSP, the technical areas were

further divided into details namely technical items. Technical areas and items are the important

basic units for the activities of technical training and guidance in the Project, in the respects of the

manual formulation, training plan, technical evaluation and so on. They are commonly used

between three major training related documents i.e. the Teaching Guidance, the Manual for Drilling

Works and the Manual for Well Rehabilitation and Tool Fishing, as shown in Table 2.

Table 2 Technical Area / Item Covered by Teaching Guidance and Manuals

Manual for Well

Teaching

Manual for

TA Code

Technical Area / Item

Rehabilitation and

Guidance

Drilling Works

Tool Fishing

Site Mobilization

✔

1-1

Site Preparation and Drilling Machine Setting-Out

✔

Drilling Tools and Equipment

✔

2-1

Selection of drilling bit and drilling method

✔

2-2

Rotary Bits

✔

2-3

DTH and DTH Bit

✔

2-4

Rig Accessory

✔

2-5

Casing Tools

✔

2-6

Drilling Equipment

✔

2-7

Drilling Calculation

✔

2-8

Weight of drilling tools

✔

2-9

Rotary bit rotation speed and weight on bit

✔

2-10

DTH Bit rotation speed and weight on bit

✔

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

Manual for Well

Teaching

Manual for

TA Code

Technical Area / Item

Rehabilitation and

Guidance

Drilling Works

Tool Fishing

Drilling Drawbacks

✔

3-1

Countermeasures against lost circulation during mud

✔

drilling

3-2

Countermeasures against lost circulation during DTH

✔

drilling

3-3

Countermeasures against bore wall collapse during mud

✔

drilling

3-4

Countermeasures against bore wall collapse during DTH

✔

drilling

3-5

Countermeasures against jamming of drilling tools

✔

Drilling Control

✔

4-1

Mud control

✔

4-2

Mud Pump Operation

✔

4-3

Casing for mud drilling

✔

4-4

Drilling operation for mud drilling

✔

4-5

Bit control and repairing for mud drilling

✔

4-6

Air control for DTH drilling

✔

4-7

Air compressor operation

✔

4-8

Casing for DTH drilling

✔

4-9

Drilling operation for DTH drilling

✔

4-10

Bit control and repairing for DTH drilling

✔

Borehole Logging

✔

5-1

Borehole logging instruments

✔

5-2

Interpretation of borehole logging results

✔

Casing Program / Installation

✔

6-1

PVC casing, screen pipe

✔

6-2

Casing Program

✔

6-3

Role of centralizer

✔

6-4

Casing, screen pipe installation

✔

Gravel Packing

✔

7-1

Determination of gravel size

✔

7-2

Calculation of gravel volume

✔

7-3

Gravel packing

✔

Well Development

✔

8-1

Well cleaning after drilling

✔

8-2

Single-tube method air-lifting

✔

8-3

Double-tube method air-lifting

✔

Back-Filling & Surface Cementing

✔

9-1

Back-filling

✔

9-2

Surface cementing

✔

Site Demobilization

✔

10-1

Precautions upon site demobilization

✔

Well Investigation

✔

11-1

Necessary information of well rehabilitation plan

✔

11-2

Well rehibilitation plan

✔

Tool Fishing

✔

12-1

Tool fishing plan

✔

12-2

Fishing tools

✔

Well Rehabilitatation

✔

13-1

Phenomenan and causes of well deterioration

✔

13-2

Methods of well rehabilitation

✔

13-3

Usage of well camera

✔

Pumping Test

✔

14-1

Purpose and methods of Pumping Test

✔

14-2

Pumping test equipment

✔

14-3

Selection of Submersible Pump

✔

14-4

Interpretation of test results

✔

Water Quality Analysis

✔

15-1

Purpose of Water quality analysis

✔

15-2

Item of water quality analysis

✔

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

2 DRILLING TOOLS AND EQUIPMENT (TA CODE 2)

2.1 SELECTION OF DRILLING BIT AND DRILLING METHOD (TA CODE 2-1)

2.1.1 PRICIPLES OF DTH, MUD AND CABLE AND TOOL DRILLING

(1) Types of Drilling Rig

Hydrogeology/ Drilling as an option has a major activities namely as;

1. Prospecting for groundwater

2. Drilling and well construction

Prospecting for groundwater deals with the investigation of groundwater existing at certain areas.

The aim of this task is to allocate well sites to produce water for human consumption. But a

geologist after this prediction is yet to prove weather his work is successful unless the water is

exploited.

The task of exploitation is given to the drillers. The driller sinks the well through the earth to

strike water from underground and takes it out to the surface to accomplish the task of drilling and

well construction. This work is done by the aid of drilling machine called a rig.

What is a Rig

A rig is a device , which is used to penetrate through the earth to a certain depth underground to

exploit minerals for human consumption.

Types of Rigs

1. Cable and tool percussive drilling (percussion )

2. Rotary drill rig

(schramn, xu 600 , pilcon, Romanian, Diamond)

3. Percussive rotary drill rig (schramn, aquadrll etc )

4. Core rotary drill rigs(, xu 600, pilcon, diamond)

5. Reverse circulation rotary drill rigs (Romanian)

EXPLANATION OF DRILLING RIGS

a. Rotary Rigs ;

This type of rig is designed to drill by applying rotation to the drilling

head driven by hydraulic oil pressure, which eventually drives the drilling string to

rotate . Bits like roller , alloyed bit and short bits are used.

b. Percussive Rotary Rigs;

In this type of rig the rotation application is quite the

same , except that the bit is connected

c. Cable and tool Percussive Rig;

This type of drilling method is accomplished by

regular lifting and dropping of a strings of tools. This phenomenon is aided by means of

connecting rod crank mechanism of oscillating movement to the locker frame. The

rocker frame ,the drum with a rope, which has the connection to the pulley and drilling

string.

d. Core Rotary Rigs ;

In this type of rig the drilling method is to drill and take out

cores instead of rocks dust ( rock cuttings ) Hollow bit and core barrel are used drilling

tools

e. Reverse Circulation Method;

In this method of drilling, setting of the circulation

system is reversible, that means the fluid flows hydraulically in the well, and then the

cuttings are uplifted inside the drill pipe up to the swivel where the sucktion hose is

connected to let out cuttings to the pump which eventually pumps the cuttings out to the

mud pit.

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

(2) Drilling Methods

There are various drilling methods, because of geological conditions range from completely

unconsolidated sediments such as alluvial sand and gravel to hard rock such as basalt and granite.

It is obviously then , that no single drilling methods is best for all geological conditions and well

installations successfully drilling in both , an art developed from long experience and application of

good engineering practices.

Well construction usually comprises five distinct operations

a. Drilling operations

b. Installing the casing

c. Placing a screen and filter pack

d. Developing well to ensure sand free operation at maximum yield(pumping test

)

e. Well completion

The term well drilling method is being used here to include all methods used in creating holes in

the era and for well construction purposes. It includes methods like boring and driving which are

not drilling methods in a pure sense.

Three drilling methods which are employed in DDCA are 1) DTH drilling method, 2) Mud rotary

drilling method and 3) Cable and tool drilling method. Mud rotary drilling methods and Cable

and tool drilling method are regarded as the types of Mud drilling methods. Cable and tool

drilling rigs are used for cable and tool drilling method, while rotary cum drilling rigs are used for

both Mud rotary drilling method and DTH drilling method. In this manual, drilling techniques of

DTH drilling and Mud rotary drilling are described as the drilling equipment to be hired to the

private drilling companies are of the type of DTH cum rotary. Principles of each drilling methods

are described below.

1) DTH Drilling Method

The (DTH) down the hole hammer

② Mud is injected

is rotary percussive tool, which

into the well by

the mud pump though

① Mud is vacuumed from the mud

operates at the bottom of the end of

the drill pipe.

pit to the mud pump

the hole being drilled. It is attached

mud pump

at the end of the drill string and

truck-mouted

down the center of the drill string

rig

mud pit

into the hammer. The air operates a

piston within the hammer, which

④ Mud is pumpred to the mud

strikes the rear end of the drill bit

pit. Drill cutting settle down

drill

providing a percussive action. The

drilled

in the mud pit.

pipe

pneumatic drill can be used on any

hole

standard rotary rig with an air

③ Upward mud flow from the

drilling

compressor of sufficient capacity.

bit trasnports drill

bit

cutting.

It is used for fast and economical

Figure 1 Mechanism of DTH Drilling Method

drilling of medium to extremely

hard formation. Fast penetration

results from the air piston blows

are transmitted directly to the bit without losing energy through the string. Figure 1 show the

mechanism of DTH drilling method.

Performance varies with different makes of DHH but as an example a particular hammer

provided with 8 BARS (116Psi) air pressure will deliver 15.5 blows per second at the piston

striking the bit and with 14 BARS

(250Psi) air pressure will deliver 23 blows per second.

In water well drilling particularly air pressure must also overcome ground water pressure when

encountered. When drilling under the head of water, a back pressure is exerted against the air

pressure of the hammer and as the air pressure is less the back pressure approaches the minimum

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

operating pressure of the hammer penetration rates will gradually fall to zero, and in the fact the

hammer will cease to operate.

2) Mud Rotary Drilling Method

In this method, action is

② Mud is injected

accomplished by rotating a drill

into the well by

the mud pump though

① Mud is vacuumed from the mud

pipe by means of a power driven

the drill pipe.

pit to the mud pump

rotary table or top-head type

mud pump

swivel, with a bit cuts and breaks

up the material as it penetrates the

truck-mouted

formation. Drilling fluid for mud

rig

mud pit

is pumped through the rotating

drill pipe and through the hole

④ Mud is pumpred to the mud

picking up material broken by the

pit. Drill cutting settle down

drill

bit. Then flow upwards in the

in the mud pit.

pipe

drilled

space outside the drill pipe,

hole

carrying the cutting to the ground

③ Upward mud flow from the

drilling

surface, and clearing the hole.

bit trasnports drill

bit

The greater fluid flow the faster

cutting.

the drilling. The drill pipe and

Figure 2 Mechanism of Mud Rotary Drilling

bit move downward deepening the

Method

hole as the operation proceeds.

At the surface, drilling mud flows into a ditch to a settling pit where the cuttings settle to the

bottom. From the settling pit the fluid overflows into another pit from which it is picked up

through the suction hose of the mud pump and re-circulated through the drill pipe. In thr mud

rotary drilling method the casing pipe is not introduced until the drilling operations are

completed. The walls of the hole are held in place by the pressure of the mud against the sides

of the hole. Figure 2 shows the mechanism of mud rotary drilling method.

3) Cable Tool Method

The cable tool drills which drills by

means of lifting and dropping as many as

60 times a minute, a drill bit to break-up

and loose the material in well crushing

and breaking the formation material

The cable tool method has survived for

thousands of years because it is reliable

for a wide variety of geological conditions.

Figure 3

The tool method offer the following

advantages

1. Drilling are relatively inexpensive

2. Rig have low energy requirements

3. Rig are simple in design and

require

little

sophisticated

maintenance

4. Well are stabilized during the

entire operation

5. Taking samples is possible

from every depth

Figure 3 Structure of Cable and Tool Drilling

Machine

6. Well can be constructed with

little chance of contamination

7. Only 2 person are needed to operate rig

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

8. Well can be drilled in area where little water exist

9. Rig can be operated in all temperature regions

10. Well can be drilled in formation where loosen circulation is a problem

11. Well can be bailed at any time to determine the approximately field

DISADVNTAGES OF CABLE TOOL METHOD / METHOD ARE

1. Productive output measured in hole produced per day is low

2. In hard rock’s where penetration rate may be very low

3. When casing is required , deep drilling presents problems in keeping the casing free

4. The heavy hammering action causes disturbance and damage in same formation

2.1.2 SELECTION OF DRILLING METHODS AND BITS ACCORDING TO GEOLOGICAL CONDITIONS

A drilling method is to be selected principally based on their performance for types of geological

formations, as shown in Table 3.

Table 3 Drilling Performance of Drilling Methods for Type of Formation

Type of Formation

Cable and Tool

Mud Rotary

DTH

Dune sand

Difficult

Rapid

Not recommended

Loose sand and gravel

Difficult

Rapid

Not recommended

Quicksand

Difficult, except in thin

Rapid

Not recommended

streaks. Requires a string of

drive pipe.

Loose boulders in alluvial

Difficult - slow but

Difficult, Frequently

Not recommended

fans or glacial drift

generally can be handled by

impossible

driving pipe.

Clay and silt

Slow

Rapid

Not recommended

Firm shale

Rapid

Not recommended

Sticky shale

Slow

Rapid

Not recommended

Brittle shale

Rapid

Not recommended

Sandstone - poorly

Rapid

Not recommended

cemented

Sandstone - well cemented

Fair

Slow

Not recommended

Chert nodules

Slow

Not recommended

Limestone

Slow

Rapid

Very Rapid

Limestone with chert

Very Slow

Slow

Very Rapid

nodules

Limestone with small

Very Slow

Slow

Very Rapid

cracks or fractures

Limestone cavernous

Very Slow

Slow to impossible

Difficult

Dolomite

Very Slow

Rapid

Very Rapid

Basalts, thin layers in

Slow

Very Rapid

sedimentary rocks

Basalts - thick layers

Slow

Rapid

Metamorphic rocks

Slow

Rapid

Granite

Slow

Rapid

Source: Drillers Training and Reference Manual

Though the cable and tool method is effective for the collapsible and/or large size gravel layer, the

mud rotary cum DTH method can cover larger range of geological conditions. Therefore, the

major drilling methods which are used in DDCA are the mud rotary and the DTH methods.

Rotary cum DTH drilling rigs correspond to both DTH methods and mud rotary method.

Therefore, suitable drilling method and bits are selected basically according to the hardness and

collapsibility of the formations.

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

Table 4 Selection of Bit for Rotary Cum DTH Drilling

Formation

Drilling Method

Bit

Drag Bits are used used for

very soft and unconsolidated

formations such as clay and

sand.

Soft

Mud Rotary

Formation

Tri-cone tooth bits are

used for soft to hard

formations. The tooth of

cone is long for soft

formation and short for

hard formation.

Medium

Mud Rotary

Formation

Carbide Button Bit is used for hard

formation. This type of bits needs

the certain weight on bit in order to

obtain the proper drilling progress

(more than 3 tons). Therefore it is

not suitable for small capacity drilling

rigs.

Hard

Mud Rotary

Formation

The down the hole hammer (DTH) is

suitable for very hard and consolidated

formations. They are used for

waterwell drilling in most of the areas of

the mainland of Tanzania.

Very Hard

DTH

Formation

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

2.2 ROTARY BITS (TA CODE 2-2)

As shown in Table 4, DDCA uses the three types of rotary bit i.e. drag bit, tri-cone tooth bit and

carbide button bit. Commonly to each type of rotary bit, a bit has a pin connection of API Regular

(Reg.) standard. The Table 5 shows the connections of each size of the rotary bits.

Table 5 Connection of Rotary Bit

Bit Size

Connection

3-1/2” - 4-1/2”

2-3/8” Reg. Pin

4-3/2-4” - 5-1/8”

2-7/8” Reg. Pin

5-3/8” - 7-3/8”

3-1/2” Reg. Pn

7-7/8” - 9”

4-1/2” Reg. Pin

9-5/8” - 15”

6-5/8” Reg. Pin

Figure 4 shows the structure of

tri-cone tooth bit.

The drillers

shall execute the following bit

control to realize the proper

drilling operation:

Prompt checking of wearing

and cleaning of bit after

pulling-out from the hole,

Checking of diameter to

prevent from the decrease of

hole diameter. In case of drag

bits, standard diameter shall be

kept by welding,

Record of bit operation hours

with necessary information

such as rotation speed, weight

on bit, pump pressure etc.

Source: Australian Drilling Industry Training Committee Limited

Figure 4 Structure of Tri-cone Tooth Bit

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

2.3 DTH AND DTH BIT (TA CODE 2-3)

Figure 5 shows the structure of DTH. The DTH is a rotary

percussive tool which operates at the bottom of the hole being

drilled. It is attached at the end of the drill string, and

string into the hammer. The air operates a piston within the

hammer which strikes the rear end of the drill bit providing a

percussive action. Porting, and in some cases valves within

the hammer cause the piston to return to the upward position

and then strike again in a continuous sequence. The hammer

and drill string is rotated by the drilling machine on the surface

which also provides necessary feed force, or, in a deep hole

feed hold back force. Air exhausted from the hammer

operation and additional air by-passed through the hammer is

then used to cool the drill bit and evacuate drill cuttings from

the hole. The DTH is very effective in drilling hard rock and

the essential difference to rotary drilling is that the percussive

rock breaking effort is being conducted on the hole bottom.

Feed forces are only required to keep to bit on the bottom of the

hole and any further effort

(feed force) will not increase

penetration but damage the hammer tool. Experienced rotary

drillers shold guard againt a natural tendency to overfeed.

Figure 6 shows the structure of DTH bits. Hammers provide

light rigs with the ability to drill hard rodk; rock that cannot be

drilled economically or quickly using any other method unless

a much heavier rig is available.

For most hammer drilling, button bits provide lower costs per

meter drilled as they give:

 Faster penetration and

 Longer runs between grinding.

The button bit drills more efficiently because the percussive

forces are distributed over the bottom of the hole. Chisel or

cross bits concentrate the energy at the centre of the hole.

Most of the outer edge is without effective cutting points.

Source: Atlas Copco

Figure 5 Structure of DTH

Source: Australian Drilling Industry Training Committee

Figure 6 Structure of DTH Bits

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However, cross “X” or insert bits are more resistant to heavy gauge wear. In some formations,

insert bits drill straighter than button bits, and in softer formations which are “scooped out” rather

than shattered, insert bits can give better penetration. Button bits are available, with buttons of

varying sizes to suit different formations and to suit the energy output of the hammer. Button

patterns are varied to suit the rock and the hole size. Bits with a cutting edge at the back shoulder

are supplied to drill “backwards” when caving could be a problem.

In order to keep the good drilling progress, buttons of bit shall be kept being sharped. The drillers

are required to execute the proper bit sharpening by referring the manufacturer’s manual of DTH.

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2.4 RIG ACCESSORY (TA CODE 2-4)

2.4.1 CONTENTS OF RIG ACCESORY

The rig accessory shall consist of drilling string elements and handling tools. They are major

tools for the drilling works to be attached to each drilling rig. Table 6 shows the contents of rig

accessories for a set of DDCA’s new rotary cum DTH drilling rig of 150 m in capacity which are

currently under procurement. Total of 6 rigs are to be procured and they are planed to be hired to

the private drilling companies. The major components of rig accessory are drill pipes, drill collars,

subs, DTHs, DTH bits, rotary bits etc. The quantities of each element in Table 6 were calculated

for the drilling of wells of 150 m in depth by using DTH drilling method and mud drilling method.

This section describes the use and the specifications of each element for the purpose of proper use

and selection by the drillers.

Table 6 Rig Accessories DDCA’s New Drilling Rig of 150 m Capacity

No.

Description

Unit

Qty

Drill pipes 41/2'' 0.D flush type with API 31 1/2''IF BOX and pin joints

Pcs

furnished with wrech squares and steel made protectors,6m long/pc

Drilling collars 5''0.D,2''IF BOX and pin joints,furnished with wretch squares

Pcs

and steel protectors,6m long/pc

Hoisting swivel API 1/2'' IF Pin joint

Pcs

Hoisting plug API 1/2'' IF Pin joint

Pcs

Drill pipes collar hanger

Pcs

Cross over sub API 3 1/2 IF BOX and pin

Pcs

DTH Hammer assembly for 6 1/4''(150mm) hole drilling API 3 1/2 Regular pin

Assy

and 8'' to 10'' hole drillling

DTH Hammer assembly for 12''(300mm) hole drilling API 3 1/2 Regular pin

Assy

DTH Button Bit for 12''(300mm) hole drilling

Pcs

Bit sub for drill pipes/collar to 6 1/4'' DTH Hammer API 3 1/2'' Regular box

Pcs

and API 3 1/2'' IF Box joint

Bit sub for drill pipes/collar to 6 1/4'' DTH Hammer API 3 1/2'' Regular box

Pcs

and API 3 1/2'' IF Box joint

DTH Button bit for 6 1/4''(159mm) hole drilling

Pcs

DTH Button bit for 8 1/4''(216mm) hole drilling

Pcs

DTH Button bit for 10''(254mm) hole drilling

Pcs

Bit grindeer for button bit and body dressing,furnished with 15 m long high

Pcs

pressure air hose

Tricone roller bits 6 1/2'' dia

Pcs

Tricone roller bits 8 1/2'' dia

Pcs

Tricone roller bits 10 1/2'' dia

Pcs

Tricone roller bits 12 1/2'' dia

Pcs

Roller bits 8 1/2'' dia

Pcs

Roller bits 10 1/2'' dia

Pcs

Roller bits 12 1/2'' dia

Pcs

Roller bits 14 1/2'' dia

Pcs

Drag bits three winged 8 1/2'' dia

Pcs

Drag bits three winged 10 1/2'' dia

Pcs

Drag bits three winged 12 1/2'' dia

Pcs

Drag bits three winged 16 1/2'' dia

Pcs

Roller bit 16'' dia for soft formation

Pcs

Stabilizer for

6 1/4'' hole body dia,1.5m long API 3 1/2 IF BOX and pin joints

Pcs

furnished with wretch squares and steel made thread protectors on both ends

Stabilizer for

8 1/2'' hole 5'' body dia,1.5m long API 3 1/2 IF BOX and pin

joints furnished with wretch squares and steel made thread protectors on both

Pcs

ends

Stabilizer for

10'' hole 5'' body dia,1.5 long API 3 1/2 IF BOX and pin joints

Pcs

furnished with wretch squares and steel made thread protectors on both ends

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No.

Description

Unit

Qty

Stabilizer for

12'' hole 5'' body dia,1.5m long API 3 1/2 IF BOX and pin joints

Pcs

furnished with wretch squares and steel made thread protectors on both ends

2.4.2 DRILL STRING ELEMENTS

The composition of different tools and elements as rotary subs, drill rods, stabilizers, drill collars,

reamers, down the hole hammers with various bits, as well as tricone roller bit and drag bits,

starting from the pin of the rotation head and ending with the bit on the bottom of the hole, is

called “DRILL STRING”. The three major functions to be performed by the drill string

are:

a. To transmit rotation from the drill unit to the drill bit

b. To transmit feed pressure (bit weight) from the drill unit to the drill bit

c. To provide passage for air or drill fluid to the bottom of the hole to operate the down the

hole hammer, to cool the drill bit, to flush the cuttings and to lift them up to the surface.

Resulting from these three major functions, the drill string is subject to various kinds of stress such

as torsion, tension bending, buckling and compression depending upon borehole depth, hole

diameter directions etc.

Because of some fact, that almost the total length of the drill string is placed below the ground level,

that all elements of the string are connected through threads and that of the above mentioned

various kinds of stress are caused considerable wear on the whole drill string, care has to be taken

that all elements but in particular threads are in good working condition in order to avoid any

breaking in the string. Therefore it is the responsibility of the Driller in charge and of the Shift

Operators to check various elements of the drill string carefully before being lowered in the

borehole. It is once more emphasized that only equipment in proper working condition should be

used in the borehole. But also drill string handling tools as bit brakers, clamps, chain wrenches,

lifting caps, etc have to be checked before use and should also be in proper working condition.

The strongly requested checking and controls by the personnel concerned are considered as

preventive measures at the drill sites in order to avoid difficult time and money consuming

fishing work hindering drilling crews from good performance. Figure 7 shows the standard

assembly of drill string.

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 Drive shaft

The drive shaft pin of the rotation gear box is threaded with 31/2" API Reg. Pin and is the

connector from the drill unit to the drill string.

 Rotary Substitutes "SUBS"

Rotary substitutes commonly known as "SUBS" are elements of the drill string and are

used where threads of one size or type must be completed together with threads of another size or

type. These subs are called "Cross Over subs". Other subs are used as wear prevention at

connection points that are frequently made up and broken out. These subs are called "Saver Subs."

Casing driver subs are to connect steel surface/conductor casing to the top drive head of

the rig. This enables the drilling by the casing or the mud/air circulation to remove the

sediment which disturbs the casing installation to the desired depth. DDCA has casing

driver subs for 65/8", 85/8", 103/4", 123/4" and14" O.D casings with API 5L line pipe thread;

the connector is 31/2 API IF Box.

Elements of the drill string which are used with our rotary rigs and which have to be coupled in

the drill string with the help of subs are as follows:

 Drill Pipes and Drill Collars

Drill pipe is a type of piping used on a drilling rig. It helps with wellbore drilling, which is the

process of digging a hole in the ground in order to access a particular natural resource, such as oil

or water. The pipe pumps drilling fluid, which generates pressure to keep unwanted fluids out of

the liquid pumped, removes drill cuttings, and helps to cool and clean the drill bit. It is one of

the most significant member of the drill string. It is available in different diameters

according to requirements, as FLUSH JOINT DRILL ROD AND UPSET DRILL ROD,

(here the tool joint is larger in diameter than the pipe itself). Tool joints are threaded with

male and female threads for connecting in the drill string. The material of drill pipes is

considered of having the best physical properties and to provide a combination of hardness,

strength and ductility.

DDCA has various size of drilling pipes such as:



51/2" O.D Fitted with 31/2" API IF Box Pin



51/4" O.D fitted with 31/2" API Reg. Box Pin



41/2" O.D fitted with 31/2" API Reg. Box Pin



31/2" O.D fitted with 23/8" API IF Box Pin



31/2" O.D fitted with 27/8" API IF Box Pin.

The drillers are required to correctly grasp the specifications of drill pipes which they use,

i.e. nominal diameter, connection (API Reg. or IF), outside and inside diameters, unit

weight. Table 7 show the general capacity of API drill pipes

Table 7 Capacity of API Drill Pipe

Nominal

Threads

Unit Weight

OD (mm)

ID (mm)

Diameter

/ inch

(kg / m)

2-3/8”

11.0

2-7/8”

54.6

17.0

3-1/2”

88.9

70.3

21.0

4-1/2”

114.3

97.1

27.0

5-1/2”

139.7

121.4

32.7

Drill collar is heavy weight pipe which shall be connected between rotary bit and drill pipes. In

water well drilling, one to three tons of drill collars is used and the weight on bit shall be within the

total weight of drill collars. Table 8 shows the general capacity of API drill collars.

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Table 8 Capacity of API Drill Collar

Connection

OD (inch)

ID (inch)

Unit Weight (kg/m)

NC23-31

3-1/8"

1-1/4"

NC26-35 (2-3/8 IF)

3-1/2

1-1/2"

39.7

NC31-41 (2-7/8 IF)

4-1/8"

51.6

NC35-47

4-3/4"

73.8

NC38-50(3-1/2 IF)

2-1/4"

79.3

NC44-60

2-1/4"

122.9

NC44-60

2-13/16"

113.0

NC44-62

6-1/4"

2-1/4"

134.7

NC46-62(4IF)

6-1/4"

2-13/16"

124.7

NC46-65(4IF)

6-1/2"

2-1/4"

148.0

NC46-65(4IF)

6-1/2"

2-1/4"

138.1

NC46-67 (4 IF)

6-3/4"

2-13/16"

160.7

NC50-70 (4 1/2 IF)

2-13/16"

174.1

NC50-70 (4 1/2 IF)

2-13/16"

165.2

NC50-72 (4 1/2 IF)

7-1/4"

2-13/16"

178.6

NC56-77

7-3/4"

2-13/16"

208.3

NC 56-80

2-13/16"

224.7

6-5/8REG

8-1/4"

2-13/16"

241.1

NC61-90

2-13/16"

291.7

7-5/8R E G

9-1/2"

322.9

NC70-97

9-3/4"

342.3

NC70-100

10"

361.6

NC77-110

11"

445.0

 Stabilizer or/and Reamer

There are a number of stabilizers and reamers manufactured of different type and use in drilling

boreholes. There is the rubber stabilizer used almost only in deep oil well or water well drilling.

More common is the welded blade type stabilizer or reamer in shallow water well drilling. It is

especially effective in soft formation where "balling up" of mud and cuttings on the drill string may

be a problem. These stabilizers are generally used for the following purpose:

 To avoid crocked hole drilling

 To center the part of the drill string under weight (mostly drill collars) and to make the drill

string more stiff although using more weight.

 To prevent the bit from wandering.

But there are also special reamers or hole openers known, placed immediately above the bit in

order to stabilize the bit but also to enlarge the borehole immediately after the pilot bit. (e.g.

Carbide Insert Blade Bit Assy.). DDCA has some kinds of stabilizer sucy as 65/8" O.D fitted

with 41/2" API Reg. Box Pin.

 Down the Hole Hammer (DTH), Bits, Drag Bits, Roller Bits

These tools as members of the drill string are doing the actual drilling work on the lower end of the

drill string on the bottom of the borehole. These tools are designed and manufactured in a wide

variety in order to meet the demand originating from the property of the underground to be

penetrated.

DTH

In order to overcome these problems which may result from lack of experience or proper

knowledge of the matter by the rig operators in addition to the above given hints each driller shall

refer to the operation and maintenance manual of the manufacturer of DTH. One copy will have

to be with a driller incharge for the purpose of training his crew and the other copy always to be

available at the drill site for the shift operators disposal in order to have information required when

on duty. The operation and Maintenance Manual shall contain all necessary general information

on:

 Preparation for Drilling

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 Drilling Operation

 Maintenance(sharpening bit) which have to be studied and followed thoroughly by the rig

operators and considered as a working guide in order to improve performance of this very

expensive equipment. Emphasis has especially to be put on the “CAUTIONS” mentioned in

the Operation and Maintenance Manual indicating the most decisive actions for proper

operation service and maintenance of the equipment.

 In addition to the instructions and guidelines given above general cleanliness at the site

proper handling of drill string as well as use of proper drill oil has to be put on the

“CAUTIONS” mentioned in the Operation and Maintenance Manual indicating the most

decisive actions for proper operation service and maintenance of the equipment.

 In addition to the instructions and guideline given above general cleanliness at the site proper

handling of drill string as well as use of proper drill oil has to be maintained. Proper drill

sting handling tools have to be used in order to avoid damages of Megadrills and Megabits

and to avoid general failure. Consultation of Senior Inspector Drilling or Drilling

Superintendent should get more common in future in case of problems with equipment or

low penetration rate in order to seek advices for improving performance of tools.

DDCA has DTH such asMission Mega and Hammer drills as follows:

 Model A 53-15

fitted with 31/2" API Reg. Box

 Model A 63-15

fitted with 41/2" API Reg. Pin

 Model A 100-10 fitted with 65/8" API Reg. Pin

 Model A 51-20

fitted with 31/2" API Reg. Box

 Model A 43-15

fitted with 25/8" API Reg. Box

Drag Bits, Tri-cone Bits and Tri-cone Roller Bits

These three types of rotary bits are major types for DDCA’s drilling works. Please refer to section

2-1 and 2-2 of this manual for the further explanation.

2.4.3 IDENTIFICATION OF SIZE AND TYPE OF THREADS

Operational trouble may sometimes be caused by not having the right tool-at the right place at the

right time. But the Driller incharge as well as the stores staff must be able to identify threads of

drill rods, bits, stabilizers and other tools of the drill string as well as threads of subs which are

required to assemble the drill string. Identification of threads manufactured according to

API-Standard is possible by measuring the PIN BASE DIAMETER and COUNTER BORE

DIAMETER at box mouth as well as by determination of threads per inch. Table 9 shows an

identification chart and instructions giving how to identify properly threads and how to determine

on the subs required at drill sites for the drilling operation.

Table 9 Identification of API Threads

Thread Type

Thread per inch

Thread Angle

Pin diameter at base

Box diameter at counterbore

REG

60°

66.68

68.26

2-3/8

60°

73.05

74.61

REG

60°

76.20

77.79

2-7/8

60°

86.13

87.71

REG

60°

88.90

90.49

3-1/2

60°

101.45

102.79

60°

102.01

103.58

REG

60°

117.48

119.06

4-1/2

60°

121.72

123.83

60°

133.35

134.94

6-5/8

REG

60°

152.20

153.99

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2.5 CASING TOOLS (TA CODE 2-5)

2.5.1 SIZE AND TYPE OF STEEL CASING PIPE

(1) Steel Casing Pipes

The steel casing pipes are used as the surface casing and/or the conductor casing. DDCA has

various types and standards of steel casing pipes. Normally, casing pipes are used as temporary

casings. Therefore they are pulled out from the borehole after the completion. In this reason

casing pipes are with threaded flush for the easiness of the handling. Stadards of API 5L-B, JIS

STPG Sch-40, JIS SGP, DIN Medium are popularly used for the steel casing. Their sizes are shown

in Table 10, Table 11, Table 12 and Table 13.

Table 10 Size of API 5L-B Steel Pipes

Thickness

Unit Weight

OD(mm)

ID(mm)

(mm)

(inch)

(mm)

(kg/m)

3-1/2"

88.9

80.9

8.37

3-1/2"

88.9

79.3

4.8

9.95

3-1/2"

88.9

77.9

5.5

11.31

4-1/2"

114.3

104.7

4.8

12.96

4-1/2"

114.3

103.9

5.2

13.99

4-1/2"

114.3

103.1

5.6

15.01

4-1/2"

114.3

102.3

16.02

6-5/8"

168.3

158.7

4.8

19.35

6-5/8"

168.3

157.1

5.6

22.47

6-5/8"

168.3

154.1

7.1

28.22

6-5/8"

168.3

152.5

7.9

31.25

8-5/8"

219.1

207.9

5.6

29.48

8-5/8"

219.1

206.3

6.4

33.57

8-5/8"

219.1

205.1

36.61

8-5/8"

219.1

203.3

7.9

41.14

8-5/8"

219.1

202.7

8.2

42.65

8-5/8"

219.1

201.7

8.7

45.14

8-5/8"

219.1

200.1

9.5

49.1

10-3/4"

273

260.2

6.4

42.09

10-3/4"

273

258.8

7.1

46.57

10-3/4"

273

257.4

7.8

51.03

10-3/4"

273

255.6

8.7

56.72

10-3/4"

273

254.4

9.3

60.5

12-3/4"

323.8

311

6.4

50.11

12-3/4"

323.8

309.6

7.1

55.47

12-3/4"

323.8

308

7.9

61.56

12-3/4"

323.8

307

8.4

65.35

12-3/4"

323.8

306.4

8.7

67.62

12-3/4"

323.8

304.8

9.5

73.65

12-3/4"

323.8

303.2

10.3

79.65

14"

355.6

342.8

6.4

55.11

14"

355.6

341.4

7.1

61.2

14"

355.6

339.8

7.9

67.74

14"

355.6

338.2

8.7

74.42

14"

355.6

336.6

9.5

81.08

14"

355.6

335

10.3

87.71

16"

406

393.2

6.4

63.13

16"

406

391.8

7.1

69.91

16"

406

390.2

7.9

77.63

16"

406

388.6

8.7

85.32

16"

406

387

9.5

92.98

18"

457

442.8

7.1

78.77

18"

457

441.2

7.9

87.49

18"

457

439.6

8.7

96.18

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Thickness

Unit Weight

OD(mm)

ID(mm)

(mm)

(inch)

(mm)

(kg/m)

18"

457

438

9.5

104.84

18"

457

436.4

10.3

113.46

Table 11 Size of JIS STPG Sch-40 Steel Pipes

Thickness

Unit Weight

OD(mm)

ID(mm)

(mm)

(inch)

(mm)

(kg/m)

89.1

78.1

5.5

11.3

3-1/2

101.6

90.2

5.7

13.5

100

114.3

102.3

125

139.8

126.6

6.6

21.7

150

165.2

151

7.1

27.7

200

216.3

199.9

8.2

42.1

250

267.4

248.8

9.3

59.2

300

318.5

297.9

10.3

78.3

350

355.6

333.4

11.1

94.3

400

406.4

381

12.7

123

450

457.2

428.6

14.3

156

Table 12 Size of JIS SGP Steel Pipes

Thickness

Unit Weight

OD(mm)

ID(mm)

(mm)

(inch)

(mm)

(kg/m)

89.1

80.7

4.2

8.794

3-1/2

101.6

93.2

4.2

10.089

100

114.3

105.3

4.5

12.186

125

139.8

130.8

4.5

15.015

150

165.2

155.2

19.754

175

190.7

180.1

5.3

24.2

200

216.3

204.7

5.8

30.1

225

241.8

229.4

6.2

250

267.4

254.2

6.6

42.4

300

318.5

304.7

6.9

350

355.6

339.8

7.9

67.7

400

406.4

390.6

7.9

77.6

450

457.2

441.4

7.9

87.5

Table 13 Size of BS Heavy Steel Pipes

Thickness

Unit Weight

OD(mm)

ID(mm)

(mm)

(inch)

(mm)

(kg/m)

88.75

79.05

4.85

10.0

100

114.05

103.25

5.4

14.4

125

139.65

128.85

5.4

17.8

150

165.2

154.4

5.4

21.1

Figure 8 shows the specifications chart giving indication on what tools and casings have to be used

at drill sites in order to complete boreholes of the required final diameters as requested by the

hydrogeologist. It will help the driller in charge to check at he site whether he has got the proper

tools or to enable him to arrange for the required tools and casings respectively. It should be

considered as general guideline when this type of casings is used for water well drilling.

Each of the columns is giving particulars on casings, couplings, drill bit as well as clearance in

annular spaces required to allow the drill bit to pass, to allow proper running of casing and to insert

gravel pack envelope around screens.

In column 2, 3, 4 and 7 are particulars of casings as O.D. Wall thickness and O.D of couplings

listed. Column 5 is indicating the max. Diameter of drill bit which may be run in the casings with a

clearance as shown in column 6. This clearance is a result from J.D casing column 4 and bit size

column 5. It is important for the Drillers incharge and the Shift Operator to know as what is the bit

clearance in order to avoid jamming of the drill string in the casings. In column 7 it is the O.D. of

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the casing coupling listed important for th be determination of the bit size required to run casings

without problems. Now in columns 8 and 9 the required bit sizes are listed depending from the O.D

of casings columns 2 and the O.D. of couplings column 9 in order to have the required clearance

for running casings and inserting gravel pack.

The annular space listed in column 10 is the minimum clearance required which will enable the

Driller incharge or Shift Operator to run casings without trouble provided he has not drilled a

crooked borehole and the borehole has got throughout the same required diameter.

The annular space listed in column II between casing O.D. and borehole wall refers to artificially

gravel packed boreholes drilled in unconsolidated soft soil formation where an effective gravel

envelop around the screens is required in order to get sand free water out. As already mentioned

above this chart is only giving general indication while in some instances special arrangements or

combinations of bit size and casing diameter may be necessary. But even in this respect the listed

diameter of casings and drill bits may help to find the correct decision.

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(2) PVC Casing and Screen Pipes

Most of the case in Tanzania, PVC pipes are used as the production casing and screen pipes.

DDCA mainly use the product of the PVC manufacturer, PLASCO, of which the sizes are shown in

Table 14. The products with the remarks of 4”, 5”, 6”, 8” and 10” casing are the standard casing

types.

5” casings are standard type for handpump wells and 6” casings are for wells for piped

water supply schemes, respectively.

Table 14 Size of uPVC Pipes

Unit

Thickness

Description

OD (mm)

Weight

Remarks

(mm)

(kg/m)

FLUSH FITTING DIN4925 CASE

113

3.9

FLUSH FITTING DIN4925 CASE

125

110

7.5

4.3

4" Casing

FLUSH FITTING DIN4925 CASE

140

124

5.2

5" Casing

FLUSH FITTING DIN4925 CASE

165

146

9.5

7.3

FLUSH FITTING PLASCO CASE

165

150

7.5

5.9

6" Casing

FLUSH FITTING DIN4925 CASE

200

177

11.5

10.8

FLUSH FITTING PLASCO CASE

200

182

8.6

FLUSH FITTING DIN4925 CASE

225

199

13.7

FLUSH FITTING PLASCO CASE

225

205

10.7

8" Casing

FLUSH FITTING PLASCO CASE

250

225

12.5

FLUSH FITTING DIN4925 CASE

280

248

21.3

FLUSH FITTING PLASCO CASE

280

255

12.5

16.9

10" Casing

FLUSH FITTING PLASCO CASE

315

285.4

14.8

22.4

Source: Catalog of PLASCO

2.5.2 CASING HANDLING TOOLS

Steel or wooden clampes, or casing elevators (See Figure 9) are usually used to install and/or pull

out the casing string. In addition, wire slings and shackles shall be prepared on site according to

the total weight of the casing string.

Figure 9 Casing Lifting Tools

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2.6 DRILLING EQUIPMENT (TA CODE 2-6)

This section describes the major equipment for drilling works by rotary cum DTH drilling. It

consists of drilling rig, mud pump, air-compressor, cargo truck and water tank truck. DDCA is

currently procuring new drilling equipment including two drilling rigs of 300 m depth, six drilling

rigs of 150 m depth and supporting equipment and trucks.

Drillers are required to evaluate the capacity of each equipment whether or not capable to drill a

borehole of various depth, diameter and drilling method. The representative capacity of each

equipment is described below.

2.6.1 SPECIFICATION OF DRILLING RIG

Figure

10 shows the structure of

standard truck-mounted drilling rig.

Besides rig plan, generally either a

mud pump or an air-compressor is

equipped on the truck.

The representative capacity of a

drilling rig is lifting capacity

(ton).

This capacity expresses the maximum

length of drill string which can be

hold and lifted up by the drilling rig.

It is directly related to the maximum

drilling depth.

If the drilling is to be executed by

DTH down to 200 m with 4-1/2” drill

pipes without drill collar, total weight

of the drill string is:

97 kg /m x 200 m = 10 tons

With consideration of stucking of

drill string,

10 to 15 % of surplus

shall be considered as a safety factor.

% of safety factor is taken,

necessary lifting capacity comes to b

11 tons.

Source: National Waterwell & Drilling Association of Australia

Prior to the selection and preparation

Figure 10 Structure of Truck-mounted Drilling Rig

of the drilling equipment, drillers shall

determine the necessary drilling tools

such as drilling pipes, drill collars, bits, DTH etc. T

total weight of the drill string is calculated and shall

evaluated whether or not within the capacity of t

drilling rig.

2.6.2 CAPACITY OF MUD PUMP

Most of DDCA’s truck-mounted rigs are equipped wi

duplex mud pump, as shown in Figure

11.

representative capacities of mud pump are the dischar

rate and the pressure.

 Discharge Rate

Necessary discharge rate shall be calculated from t

necessary annular velocity between drill pipe and ho

diameter. In general, at least 10 m/min of annular

Figure 11 Structure of Mud Pump

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velocity is necessary for the proper removal of drilled cuttings.

In case of drilling by 8” bit and 4-1/2” drill pipe:

Necessary Disharge Rate (L/min)

= Annular Volume 22 L/m x Annular Velocity 10 m/min =220 L/min

In case of drilling by 12” bit and 4-1/2” drill pipe:

Necessary Disharge Rate (L/min)

= Annular Volume 63 L/m x Annular Velocity 10 m/min =630 L/min

Therefore, approximately 600 L/min is necessary if 12” bit drilling is used.

 Pressure

Each pump has its maximum pressure according

to the discharge rate. The maximum pressure

of mud pump equipped on the DDCA’s new

drilling rig of 150 m depth is 25 bar for 600

L/min of discharge rate. Figure 12 shows an

example of separated type duplex mud pump

made by TONE and its specifications are shown

in Table 15. Discharge rate of a duplex pump

is decided by piston

(liner) diameter, stroke

length and stroke speed

(See Figure

13).

Drillers shall liner and piston of suitable

diameter for the drilling diameter and depth.

Figure 12 Duplex Mud Pump NP-700

(TONE)

Source: Australian Drilling Industry Training Cmmittee

Figure 13 Internal Structure of Mud Pump

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Table 15 Specifications of NP-700 Mud Pump

140

127

114

102

Cylinder Dia. (mm)

(5-1/2")

(5”)

(4-1/2")

(4”)

(3 一 1/2")

Discharge Rate (L/min)

615

505

405

315

235

Max. Pressure (bar)

Stroke r.p.m

Drive Shart r.p.m

395

Stroke Length (mm)

130

Valve Type

Ball or Conical

Suction Hose Dia. (mm)

100 or 75

Delivery Hose Dia. (mm)

65 or 50

Power (kw)

30-4P

Total Weight (kg)

1600

Dimension (mm)

3,040 (L) x 830 (W) x 1,575 (H)

Discharge pressure is mainly caused by the friction loss of the inside of drill pipes. Therefore, the

discharge pressure is effected by the discharge rate and inside diameter and length of drill pipes as

the following:

 Disharge pressure increases, if the discharge rate is increases,

 Disharge pressure increases, if the pipe inside diameter becomes smaller,

 Discharge pressure increases proportionally to the length of the pipe for the constant

discharge rate and pipe inside diameter.

Standard type of mud pump has the capacity of 600 L/min and 25 bar. They are sufficient for the

drilling of medium scale borehole down to 150 m with 8” to 12”. However, for large bore and/or

deep borehole drilling more than 150 m, discharge rate not less than 1,000 L/min will be necessary.

In this case, large pressure will occur if the small diameter drill pipes such as 3-1/2” are used.

Drillers are required to always check the relationship

between pipe size, depth, discharge rate and pressure to

utilize such information for the proper selection of drill

pipes and rig capacities.

2.6.3 CAPACITY OF AIR COMPRESSOR

Air-compressors for DTH drilling are of type of either

reciprocating or rotary screw.

Nowadays, rotary

screw type air-compressors are mainly used.

Representative capacities of the air-compressor are

air delivery and maximum pressure. DDCA’s new

Figure 14 Rotary Screw Air-Compressor

compressor for the drilling down to 150 m has the

PDSJ750S (21 m³/h, 21 bar)

capacities of 18.4 m³/min (650 CFM) and 17 bar

(246 psi). Figure 14 show another type of PDSJ750

air-compressor, of which air delivery is 21 m3/min

and the maximum pressure is 21 bar.

Air delivery shall be determined from the necessary

annular velocity for the proper removal of cuttings.

The optimum annular velocity is thought to be 1,220

m/min. The maximum pressure shall be not less

than the hydro static pressure of water in borehole.

If the borehole depth is 150 m, the compressor of not

less than

15 bar is preferable to be selected.

However, if the water level is deep, hydro static

Source: National Waterwell & Drilling Association of Australia

pressure becomes lower. The pressure to drive

Figure 15 Change of Drilling Speed by

Operating Pressure of DTH

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the DTH shall be considered as well. More pressure will give the better progress of the drilling.

Figure 15 shows typical performance improvement on a hammer’s speed in hard granite at varying

air pressures. Performance varies with different makes of DTH but as an example a particular

hammer provided with 7 bar air pressure will deliver 15 blows per second of the piston striking the

bit and with 14 bar air pressure will deliver 23 blows per second. In this instance where the piston

weighs 5 kg and has a stroke of 50 cm before striking the bit, some idea of the power of a DTH can

be appreciated.

2.6.4 CAPACITY OF WATER TANK TRUCK

In general, capacity of tank of water tank truck for water well drilling is

5,000 to 6,000 L.

Necessary water volume for the drilling work is though to be three times of bore volume.

The

estimation examples are shown below:

8” x 150 m

Unit bore volme: 8 x 4 = 32 L/m

Total bore volume: 32 L/m x 100 = 3,200 L

Total necessary water: 3,200 L x 3 = 9,600 L

(2 times of transportation)

12” x 150 m

Unit bore volme: 12 x 6 = 72 L/m

Total bore volume: 72 L/m x 100 = 7,200 L

Total necessary water: 7,200 L x 3 = 21,600 L

(4 to 5 times of transportation)

2.6.5 CAPACITY OF CARGO TRUCK

The representative capacities of cargo

truck are gross vehicle weight and

payload. The payload is the maximum

load acceptable to the truk. The gross

vehicle weight is the total of truck

weight and the payload. DDCA’s new

cargo truck has a capacity of 10 tons of

payload

(See Figure

16).

This can

load approximately 370 m of 4-1/2” drill

pipe (unit weight 27 kg/m).

Figure 16 DDCA’s New Cargo Truck

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2.7 DRILLING CALCULATION (TA CODE 2-7)

2.7.1 UNIT CONVERSION

During the drilling works, drillers are required to observe and calculate the various values from

materials and equipment actions such as weight, pressure, discharge rate etc. These values are

expressed in different unit system such as metric, imperial etc. Therefore, drillers shall acquire

the knowledge of the conversion between different unit systems. This section describes the major

units to be used for the drilling works and gives the reference for the unit conversion. Examples of

unit conversion using conversion tables are given below:

Length

100

inch

2.54

100

3.937

inch

3.048

164.05

Discharge

1000

gal/hr

3.785

m3/hr

264.2

gal/hr

m3/day

0.04167

m3/hr

600

m3/day

200

l/min

m3/hr

800

l/min

100

m3/hr

27.78

l/s

100

l/s

360

m3/hr

Pressure

1,000

Kgf/cm2

98.1

MPa

Kgf/cm2

Conversion Table

Length

3.281

39.37

0.3048

0.0254

0.0833

Volume

gal

264.17

gal

0.003785

Pressure

kN/m2

kgf/cm2

bar

lbf/in2(psi)

(kPa)

kgf/cm2

0.981

98.1

14.223

bar

1.02

100

14.504

kN/m2

0.0102

0.0098

0.145

(kPa)

lbf/in2(psi)

0.0703

0.0689

6.89

In the following pages, useful conversion factors and conversion tables are provided.

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2.8 WEIGHT OF DRILLING TOOLS (TA CODE 2-8)

The elements of the drill string is described in Section 2-4 Rig Accessory of this manual. This

section explains how to express the drill string assembly and how to calculate the total weight of

the drill string.

2.8.1 DRILL STRING ASSEMBLY

Prior to the decision of drill string assembly, necessary tools shall be listed up with their capacities

before the determination of drill string assembly. Example of drill string assembly is shown in

Table 26, DP: Drill Pipe, DC: Drill Collar, ST: Stabilizer

Table 27 and Table 28. These examples are for the mud drilling of 2stages. The 1^st stage is

drilling by 12-1/4” bit down to 30 m and the 2^nd is drilling by 8-1/2” bit down to 100 m. At first,

necessary drilling tools for 12-1/4” drilling and 8-1/2” drilling shall be listed up as shown in Table

26. Then, the drill string assemblies are determined respectively for 12-1/4” drilling and 8-1/2”

drilling as shown in DP: Drill Pipe, DC: Drill Collar, ST: Stabilizer

Table 27 and Table 28.

Table 26 List of Necessary Tools for 12-1/4” and 8-1/2” Drilling

Connection

Unit Length

Tool

Top

Bottom

(m)

4-1/2" DP

3-1/2" IF Box

3-1/2" IF Pin

6-1/4" ST

4" IF Box

4" IF Pin

1.2

6-1/4" DC

4" IF Box

4" IF Pin

8-1/4" ST

6-5/8" Reg Box

6-5/8" Reg Pin

1.2

8-1/4" DC

6-5/8" Reg Box

6-5/8" Reg Pin

8-1/2" Tri-Cone Bit

4-1/2" Reg Pin

0.6

12-1/4" Tri-Cone Bit

6-5/8" Reg Pin

0.8

Crossover Sub

3-1/2" IF Box

6-5/8" Reg Pin

0.6

Bit Sub

6-5/8" Reg Box

0.6

DP: Drill Pipe, DC: Drill Collar, ST: Stabilizer

Table 27 Drill String Assembly for 12-1/4” x 30 m Drilling

Connection

Unit Length

Tool

Qty.

Length (m)

Top

Bottom

(m)

4-1/2" DP

3-1/2" IF Box

3-1/2" IF Pin

Crossover Sub

3-1/2" IF Box

6-5/8" Reg Pin

0.6

8-1/4" DC

6-5/8" Reg Box

6-5/8" Reg Pin

8-1/4" ST

6-5/8" Reg Box

6-5/8" Reg Pin

1.2

Sub

6-5/8" Reg Box

4-1/2"Reg Box

0.6

12-1/4" Tri-Cone Bit

6-5/8" Reg Pin

0.6

Total Length (m)

Table 28 Drill String Assembly for 8-1/2” x 100 m Drilling

Connection

Unit Length

Tool

Qty.

Length (m)

Top

Bottom

(m)

4-1/2" DP

3-1/2" IF Box

3-1/2" IF Pin

Crossover Sub

3-1/2" IF Box

4"IF Box

0.6

6-1/4" DC

4" IF Box

4" IF Pin

6-1/4" ST

4" IF Box

4" IF Pin

1.2

Bit Sub

4" IF Box

6-5/8" Reg Box

0.6

12-1/4" Tri-Cone Bit

6-5/8" Reg Pin

0.6

Total Length (m)

105

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2.8.2 WEIGHT CALCULATION

Total weight of the drill string assemblies are calculated for each. The weights of bits, subs,

stabilizers can be included in those of driller pipes or drill collars, as they are not heavy comparing

to the total weight.

Table 29 Weight Calculation of Drill String Assembly for 12-1/4” x 30 m Drilling

Tool

Unit Weight (kg/m)

Length (m)

Weight (kg)

4-1/2" DP

729

8-1/4" DC

241

1,446

Total

2,175

Table 30 Weight Calculation of Drill String Assembly for 8-1/2” x 100 m Drilling

Tool

Unit Weight (kg/m)

Length (m)

Weight (kg)

4-1/2" DP

2,268

6-1/4" DC

125

2,625

Total

105

4,893

As a result, total weight is 2.2 tons for 12-1/4” drilling and 4.9 tons for 8-1/2” drilling. Therefore,

with the consideration of 10 % of the safety factor for the stucking, the lifting capacity of the

drilling rig shall be not less than 5.4 tons. Furthermore, the total weight of casing pipes shall be

considered as well.

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2.9 ROTARY BIT ROTATION SPEED AND WEGHT ON BIT (TA CODE 2-9)

2.9.1 ROTATION SPEED OF BIT

At the commencement of the hole, safe and

smooth rotation and feed rates must be aimed

for any consideration. When the hole is safely

collared and drilling is proceeding, smooth

operation continues to be the prime aim, but

while maintaining smooth operation, work to

achieve the desirable thrust loadings and

rotational speed to give correct chip making.

The chip size produced by a rotary bit is

controlled by four factors:

1. nature of the formation

2. the way that the bit makes the chip

(crushing, cutting, tearing etc)

3. rotary speed

4. penetration rate

Large chips measn better samples and less

energy required to penetrate. Larger chips

also make chip clearing more difficult.:

1. the formation

2. the drill string

Source: Australian Drilling Industry Training Committee Ltd

3. the interaction between these and the

Figure 17 Bit Penetration and Rotary

drilling rig

Speed

The penetration rate improves as we increase

thrust and rotation speed. But this holds true only while the bit operates correctly. If the bit is

overloaded or runs too fast, the bearings break down, the gauge cutters wear rapidly and the chip

clearing operation bogs down. For all bits, there is a maximum thrust and speed. For most bits,

there is a minimum thrust to make them penetrate correctly.

Figure 17 shows the relationship between bit penetration and rotary speed. However, in DDCA,

the range of 30 to 100 r.p.m is employed for the rotation speed of rotary bits.

2.9.2 WEIGHT ON BIT

The weight required on any rock roller bit for effective

and Maximum Efficient Rate of Penetration (MERP)

varies directly as the compressive strength of material

being cut. This is a broad statement which is bascally

true but within which there are many variations and

exceptions. The heavy weights necessary to drill hard

formations are required to give effective crushing force

to the bit tooh and probably to keep the tool more or

less flat running bottom.

The weight shall be loaded to to the bit when drilling

the hard formations. In general, maximum weight on

bit (WOB) is thought to be 1 to 1.5 tons per inch of bit

diameter. If a bit is of 8 inches, maximum WOB is

estimated to be eight to 12 tons. However, for the

drilling of the level of

150 m boreholes, WOB is

Figure 18 Example of the

Calculation of WOB

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between the range of 1 to 3 tons. So as not to cause the damage of the drilling tools and the

deviation of the hole, the WOB shall be within the weight of drill collar. During drilling, WOB

shall be regulated by the lifting force by drive head.

Figure 18 shows an example of the calculation of the WOB for the drilling by 8-1/2” bit with 84 m

of 4-1/2” DPs and 21 m of 6-1/4” DCs. The WOB is calculated as the following:

Maximum Weight on Bit (WOB)

2.6 x 0.8 =

2.08

ton

Total Weight of Drill String

4.9

ton

Target WOB

ton

Lifting Load by Drive Head

4.9 - 2 = 2.9

ton

The maximum WOB shall be not more than 80 % of the weitght of DCs (2.6 tons), with the

consideration of the safety factor. Therefore, the target WOB was decided to be 2.0 tons. Total

weight of the drill string is 4.9 ton. In order to regulate the WOB to 2.0 tons, the drill string shall

be lifted up by the drive head. Then remaing weight of 2.9 tons are loaded on the bit as the WOB.

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2.10 DTH BIT ROTATION SPEED AND WEGHT ON BIT (TA CODE 2-10)

2.10.1 ROTATION SPEED

To start drilling, turn on air rotary slowly. Then feed down slowly until the piston starts operating.

Add just enough pulldown pressure to start breaking rock. Make sure the bit does not drift when

it first strikes the formation because this can damage the bit buttons. Always check the operation

of a DTH tool before running it into a hole. Try it out first on a solid piece of timber at the

surface. As the tool approaches the bottom of the hole, proceed and start rotation before putting

weight on the bit. The presence of water in the hole when drilling is resumed will not prevent tool

operation. Lowering the tool into the hole with the air turned on will force the water out of the hole.

Proper rotation speed is important for long bit life and optimum penetration. The recommended

speed ranges from 12 to 40 r.p.m. A slower rotation is used in hard, abrasive formations. A

faster rotation is acceptable when drilling in soft, nonabrasive formations. Ideally, the bit should

penetrate about 10 mm (3/8 in) per drill pipe revolution.

“Rule of thumb” is penetration rate in

metres-per-hour x 1.6 to obtain r.p.m about one-half of the penetration rate in feet-per-hour (Adjust

up or down several r.p.m to match formation).

2.10.2 WEIGHT ON BIT

When the bit first cotacts the formation, apply minimal weight on the bit. After a few minutes,

increase the thrust pressure to allow the tool to run smoothly. The correct optimum weight should

be monitored and maintained throughout the drilling operation. As the hole gets deeper and drill

pipe is added, the thrust pressure must be reduced to compensate for the added weight of the drill

pipe. Hydraulic pressure required to keep the optimum weight on the bit varies from rig to rig.

Principally, whole totoal weight of the drill string shall be balanced by the drill head and WOB

shall be less than one ton, so as not to cause the hole deviation. However, WOB and drilling

speed shall be carefully regulated by the driller, so that the DTH can catch up the drilling down

speed.

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3 DRILLING CONTROL (TA CODE 4)

3.1 MUD CONTROL (A CODE 4-1)

The roll of mud circulation is as follows:

 Prevension from wall collapse

 Removal of drill cuttings from the hole

 Prevension from flow-in of groundwater

 Prevension form lost circulation

 Cleaning and cooling of bit

 Reducing the friction of bit rotation

Bentonite is the most general mud stabilizer. Other mud additives are CMC, polimers and

dispersant. Viscosiity and density of the mud shall be well controlled by using the marsh funnel

and mud balance. Funnel spped shall be approximately 30 seconds and specific gravity shall be

not more than 1.2. If the mud is too strong, the cutting separation becomes non effective.

Furthermore, it may cause the stucking of the drill string. The separation work from the mud

canal is important.

Mud circulation system is composed of mud pump, suction pit, settlement pit and so on. Drillers

are required to understand the functions of each component and proper operation of the mud

circulation sysmte is important to implement the smooth drilling works. Figure 19 shows the

standard layout of drilling Figure 19equipment including the mud pits and canals.

Figure 19 Standard Layout of Drilling Equipment on Site

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3.2 MUD PUMP OPERATION (TA CODE 4-2)

The discharge rate of mud pump is important for the removal of the drill cuttings. Usual cares

shall be taken on the worn out of the parts of the mud pump, because it decreases the discharge rate.

In case that the discharge rate decreases during drilling, drill string shall be raised up to the depth

up to the safe depth (in the casing) to check the mud pump.

The pump pressure shall be kept recorded as it is an important parameters to identify the borehole

conditions. The variation of the pump pressure indicates the following conditions:

Increase of the pressure:

 Encountering clayey formations

 Mud visicosity and/or density is elevated

 Bore wall collapse

 Drill cuttings remains in the hole

 Bit is covered by the clay

 According to the increase of depth

Decrease of the pressure:

 Breakdown of the mud pump

 Mud viscosity and/or density is decreased

 Lost circulation

 Encountering sandy formations

Please refer to Technical Item 2-4 for the further specifications and structure of the mud pump.

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3.3 CASING FOR MUD DRILLING (TA CODE 4-3)

The boreholes in sedimentary formation are

normally drilled by mud drilling methods in

two stages, i.e. surface hole drilling and

production hole drilling.

Unlike DTH

drilling, conductor casing is not installed

unless collapsible and/or lost circulation

formation exists which shall be protected by

the conductor casing. Figure 20 shows an

example of the casing program for mud

drilling borehole of which production casing

and screen pipes are of 6”.

The surface casing is required when:

 Surface water must be sealed off

 Unstable formations interfere with

drilling, or

 Artesian flows are possible. in this case

the surface casing must be cemented

The purpose of surface casing is to isolate

freshwater zones so that they are not contaminated during drilling and completion.

The surface

casing is also necessary for the smooth work around the borehole during the drilling.

PVC casing and screen pipes are used for most of the boreholes in Tanzania. Please refer

Technical Item 6-1 for the specifications of PVC casing and screens and Technical Item 6-3 for the

installation procedures.

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3.4 DRILLING OPERATION FOR MUD DRILLING (TA CODE 4-4)

Figure 20 shows the process of the

drilling works by mud drilling method.

It includes many processes and

drillers are required to acquire lots of

knowledge

and

techniques.

Technical Item 1 to 15 covers all the

process and drillers can refer to each

material to conduct the works.

DDCA has the report forms for the

record of the drilling works. Drillers

shall keep proper records of their

works using these forms. Figure 21

shows an example of well completion

form and Figure

22 is another

example of well section drawing.

Figure 20 Work Flow of Mud Drilling

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