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RIVER CROSSING OF NATURAL GAS PIPE LINES: A STUDY OF BANGLADESH EXPERIENCE

MD. ASRAFUL ALAM

MASTER OF ENGINEERING IN PETROLEUM ENGINEERING

DEPARTMENT OF PETROLEUM & MINERAL RESOURCES ENGINEERING BANGLADESHUNIVERSITY OF ENGINEERING AND TECHNOLOGY DHAKA-1000, BANGLADESH

JUNE 2015 Page | 1

RIVER CROSSING OF NATURAL GAS PIPE LINES: A STUDY OF BANGLADESH EXPERIENCE

A Project By MD. ASRAFUL ALAM Roll NO: 0409132005 P

Submitted to the Department of Petroleum & Mineral Resources engineering in partial fulfillment of the requirements for the degree of MASTER OF ENGINEERING IN PETROLEUM ENGINEERING

DEPARTMENT OF PETROLEUM & MINERAL RESOURCES ENGINEERING BANGLADESHUNIVERSITY OF ENGINEERING AND TECHNOLOGY DHAKA-1000, BANGLADESH JUNE 2015 Page | 2

RECOMMENDATION OF THE BOARD OF EXAMINERS The undersigned certify that they have read and recommended to the Department of Petroleum & Mineral Resources Engineering, for acceptance, a project entitled as “RIVER

CROSSING OF NATURAL GAS PIPE LINES: A STUDY OF BANGLADESH EXPERIENCE” submitted by MD. ASRAFUL ALAM,

Roll No: 0409132005(P), Session: April 2009 in partial fulfillment of the requirements for the degree of Master of Engineering in PetroleumEngineering on June 29, 2015.

Chairman (Supervisor)

:

_________________________ Mohammad Mojammel Huque Assistant Professor Department of Petroleum & Mineral Resources Engineering BangladeshUniversity of Engineering and Technology Dhaka-1000, Bangladesh.

Member

:

______________________ Dr. Mohammad Tamim Professor and Head Department of Petroleum & Mineral Resources Engineering BangladeshUniversity of Engineering and Technology Dhaka-1000, Bangladesh.

Member

:

_______________ Afifa Tabassum Tinni Assistant Professor Department of Petroleum & Mineral Resources Engineering BangladeshUniversity of Engineering and Technology Dhaka-1000, Bangladesh.

Date: June 29, 2015

Page | 3

DECLARATION

It is hereby declared that this project or any part of it has not been submitted elsewhere for the award of any degree or diploma.

________________ Md. Asraful Alam

Page | 4

ABSTRACT Natural gas is often transported over significant distances- across rivers, hills, and other natural obstacles. River crossing is arguably the most challenging part of a land based pipeline project. Procedures and technologies for pipeline construction and river crossing have matured over the years. However, each new project offers a set of challenges and opportunities unique to that project.

In Bangladesh, pipelines were installed across a number of rivers since the beginning of commercial usage of natural gas. The Government of Bangladesh has plans to extend the natural gas network. Therefore, more river crossings will be forthcoming. It is important to examine the river crossings in Bangladesh and identify the challenges and solutions related to those projects. However, it is possible to analyze the problems and to table the common items to bring them under a systematic procedure. For Horizontal Directional Drilling (HDD), pipe site and rig site selection and development is the initial stage of a river crossing project. An unplanned or faulty selection and development of a HDD site may cause severe problems which may even jeopardize the entire pipeline project.

The natural gas transmission pipeline infrastructures in Bangladesh represent a complex mechanical system. This system has been developed over the last few years and is controlled at a very low level of sophistication. State owned organization Gas Transmission Company Limited (GTCL) under Petrobangla is now responsible for maintenance, operation and expansion of the gas transmission grid across the country. GTCL is constructing the pipeline crossing the river by HDD method with the help of international agencies who are specialized in HDD sector. Despite having the drilling experience, it is difficult to get a generalized idea on the HDD issue due to lack of compilation of the individual experience.

In this section GTCL has implemented a 60km X 30″ Bakhrabad-Siddhirganj gas transmission pipeline project having six river (Shitallakhya-556.32m, Old Brahmaputra-665.41m, Kajla657.84m, Meghna-1593.18m, Asharier-856.80m & Meghna-Gumoti-1941.87m) crossings by HDD method. Each river crossing has the unique challenges and remedial measures of six representative river crossing sites have been analyzed.

Page | 5

It is revealed that selection of right-of-way, selection of crossing location, sub-soil investigation and selection of work procedure pose the biggest and most common problem for the preconstruction activity before HDD. In general, drilling profile design, mobilization of rig unit and its accessories, selection of guidance system, selection of equipment/accessories, selection of bentonite mixing ratio and viscosity, pipe string preparation, scarcity of manpower etc. should be taken into account to plan the successful HDD project. This study also includes the nature of the problems and their reasons, degree of severity which cause time and cost overrun of the project.

Page | 6

ACKNOWLEDGEMENT At first, I am very much grateful to the most powerful, the gracious almighty Allah for giving me knowledge, energy and patience for completing the project work successfully.

In successful accomplishment of my work, I express my sincerest gratitude to all whose suggestions and guidance have been incorporated in this work. Especially, I would like to convey my gratitude to Mohammad Mojammel Huque, Assistant Professor, Department of Petroleum & Mineral Resources Engineering, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh for his supervision, guidance, encouragement, review, writing, rewriting, verification and cooperation throughout this work.

I am grateful to Dr. Mohammad Tamim, Professor and Head, Department of Petroleum & Mineral Resources Engineering, for making my thoughts wider through his distinguished lectures demonstration during class period that help me a lot in completing this work.

I am also grateful to Dr. Mohammad Mahbubur Rahman, Associate Professor, Department of Petroleum & Mineral Resources Engineering, for his valuable advice, guidance, encouragement, inspiration, cooperation and interest in this work.

I am also grateful to Afifa Tabassum Tinni, Assistant Professor, Department of Petroleum & Mineral Resources Engineering, for her valuable advice, guidance, encouragement, inspiration, cooperation and interest in this work.

I express my gratitude to the management of Gas Transmission Company Limited (GTCL) as well as Petrobangla for their support and cooperation in getting data and information that help me a lot in completing this work. I am also grateful to all who extend their helping hands specially Engr. Jameel A. Aleem, Director (Operation’s & mains), Petrobangla, Engr. Md. AinulKabir, Project Director, Engr. Md. Abdul Azim, Manager (Engg.), Bakhrabad-Siddhirganj gas transmission pipeline project, GTCLand all of GTCL in completing this work.

I also express my gratitude to the staff of Department of Petroleum & Mineral Resources Engineering for their cooperation and support. Page | 7

TABLE OF CONTENTS Page No. Chapter 1

INTRODUCTION

1.1

Objectives

Chapter 2

HORIZONTAL DIRECTIONAL DRILLING (HDD)

2.1

Importance of trenchless technology

4

2.2

HDD objectives and methodology

5

2.2.1

Pipe string preparation

6

2.2.2

Rig set up

6

2.2.3

Pilot hole

7

2.2.4

Pilot hole reaming

8

2.2.5

Swab pass

9

2.2.6

Product pipe attachment and preparation for pipe pullback

9

2.2.7

Buoyancy control

10

2.2.8

Pipe pullback

11

2.3

Brief description of HDD equipment /Accessories

12

2.3.1

Rig unit

12

2.3.2

Bottom hole assembly

12

2.3.3

Drill pipe

13

2.3.4

Drill bits

13

2.3.5

Reamer

14

2.4

Guidance system

15

2.4.1

Walk over system

16

2.4.2

Wire line steering tools system

17

2.4.3

Tru-Tracker survey system

17

2.4.4

Para-Tracker survey system

18

2.5

Drilling mud & mud recirculation unit

19

2.5.1

Drilling fluid/Drilling mud

19

2.5.2

Mud recirculation unit

20

Chapter 3

SELECTION OF HDD AS THE PREFERED CROSSING METHOD

3.1

Pipeline route selection

21

3.2

Crossing location selection

21

1

Page | 8

3.3

Crossing method selection

21

3.4

Other selection issue

22

3.4.1

Access

22

3.4.2

Drill entry & exit site selection

23

3.4.3

No drill zone

24

3.4.4

Water source

24

3.5

Risk consideration

25

3.5.1

Regulatory risk

25

3.5.2

Construction risk

26

3.5.3

Operation risk

27

3.6

Potential economic advantages of HDD

28

3.7

Cost of HDD application

28

3.7.1

Direct cost and benefits of HDD applications

29

3.7.2

Indirect cost and benefit of HDD applications

29

3.8

30

Chapter 4

Cost analysis for six river crossing in Bakhrabad-Siddhirganj gas transmission pipeline project, GTCL. ENGINEERING DESIGN CONSIDERATION

4.1

Geotechnical investigation prior to HDD

31

4.2

Borehole profile and geometry

32

4.3

Installation load

33

4.4

Pipe weight/Buoyancy

35

4.5

External coating

36

Chapter 5

CASE STUDY

5.1

Case study-01: Shitallakhya river crossing

40

5.1.2

41

5.1.3

Challenge-1: Magnetic interference problem due to space constraint and steel structure Challenge-2: Product pipe alignment problem

5.2

Case study-02: Old Brahmaputra river crossing

43

5.2.1

Challenge-1: Right-of-way mismatch

44

5.3

Case study-03: Kajla river crossing

46

5.3.1

Challenge-1: Higher entry and exit angle effect

47

5.3.2

Challenge-2: Straight right-of-way is not available

48

5.3.3

Challenge-3: Bundle pulling stuck up at kajla river crossing

49

5.4

Case study-04: Meghna river crossing

51

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42

5.4.1

Challenge-1: Difficulties of HDD pipe string preparation due to non-availability of straight right-of-way

52

5.4.2

Challenge-2: Rig anchoring arrangement

55

5.4.3

Challenge-3:Reaming operation and disposal of drilling mud

56

5.4.4

Challenge-4: Buoyancy control during pipe pullback

57

5.4.5

Challenge-5: Mechanical breakdown of mud pump during pipe pullback

58

5.5

Case study-05: Asharier river crossing

61

5.5.1

Challenge-1: Rig machine and its accessories mobilization problem---------------------------------------------------------------------Challenge-2: Drill pipe mobilization during pilot hole drilling and

62

5.5.2

reaming

63

5.6

Case study-06: Meghna-Gumoti river crossing

64

5.6.1

Challenge-1: Rig anchoring arrangement

65

5.6.2

5.6.3

5.6.4

Challenge-2: Casing pipe installation to keep the drill string more rigidity. Challenge-3: Stuck up reamer (at 690m location) retrieval using vibrating hammer technique. Challenge-4: Stuck up reamer (at 1246m location) retrieval using donut wiper and vibrating hammer technique.

67

67

69

5.6.5

Challenge-5: Buoyancy control during pipe pullback

71

5.7

Summary of case study

72

5.8

Degree of difficulties and frequency of occurrences

76

5.9

Factor that contribute HDD productivity

76

5.10 Chapter 6

Monitoring and assessing environment related issues during HDD installation

80

CONCLUSION Conclusion

85

REFERENCES

86

Appendix-A1: Engineering calculation for Meghna river crossing

88

Appendix-A2: Shitallakhya river crossing profile

96

Appendix-A3: Old Brahmaputra river crossing profile

97

Appendix-A4: Kajla river crossing profile

98

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Appendix-A5: Meghna river crossing profile

99

Appendix-A6: Asharier river crossing profile

100

Appendix-A7: Meghna-Gumoti river crossing profile

101

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LIST OF TABLE Page No. Table 2.1

Classification and characteristic of HDD rig

12

Table 3.1

Construction Risks Associated with an HDD

27

Estimated cost analysis for Six River Crossing under BakhrabadTable 3.2

Siddhirganj gas transmission pipeline project submitted by

30

international contractor Table 5.1

The name of the river which was crossed by HDD method

37

Table 5.2

Design Parameters for Shitallakhya river crossing

40

Table 5.3

Design Parameters Old Brahmaputra river crossing

43

Table 5.4

Design Parameters for Kajla river crossing

46

Table 5.5

Design Parameters for Meghna river crossing

51

Table 5.6

Design Parameters for Asharier river crossing

62

Table 5.7

Design Parameters for Meghna-Gumoti river crossing

65

Table 5.8

Evaluation of case study

72

Table 5.9

Case study summary table.

76

Table 5.10

Description of factors that contribute HDD productivity

77

Table 5.11

Summary of Noise Level Measurements

81

Table 5.12

Air Quality Monitoring Result

82

Table 5.13

Soil Quality Test Result

83

Table 5.14

Physical / Chemical/Bacteriological Analysis of River Water Sample

84

Page | 12

LIST OF FIGURES Page No. Figure 2.1 Figure 2.2

Tasks associated with HDD project Pipe string preparation

6

Figure 2.3

Rig site work space

7

Figure 2.4

Pilot hole drilling procedure

8

Figure 2.5

Reaming procedure

8

Figure 2.6

Details of Pipe Roller

9

Figure 2.7

Pipe String lifted on roller by Side Boom

9

Figure 2.8

Typical HDD site layout pipe site.

10

Figure 2.9

Typical pipe side layout with buoyancy control arrangement

11

Figure 2.10

Pipe pullback procedure

11

Figure 2.11

ure Typical rig unit

12

Figure 2.12

Bottom hole assembly (BHA).

13

Figure 2.13

Heavy wall drill pipe

13

Figure 2.14

Different type of drill bits

14

Figure 2.15

Fly cutter type reamer

14

Figure 2.16

Barrel type reamer

14

Figure 2.17

Bullet-nose type reamer

15

Figure 2.18

Conventional hole openers

15

Figure 2.19

Walk over system

16

Figure 2.20

Tru tracker survey system

17

Figure 2.21

Para-Tracker survey system

18

Figure 2.22

Mud recirculation unit

20

Figure 4.1

A typical HDD borehole profile

32

Figure 4.2

Interaction forces between the pipe and ground surface

34

Figure 4.3

Buoyancy control with water

35

Figure 5.1

Location of Bakhrabad-Siddhirganj gas transmission pipeline route on Bangladesh map.

Figure 5.1.1

Pipe string inside trench with bentonite slurry

Figure 5.2.1

Entry and exit point of pipeline on the bank of the Old Brahmaputra river Page | 13

5

38 42 44

Page No. Figure 5.2.2

Old Brahmaputra river crossing layout

45

Figure 5.3.1

Rig installation details for Kajla river

47

Figure 5.3.2

Kajla river crossing layout

48

Figure 5.3.3

Pipe pulling preparation at curve segment of right-of-way at Kajla river crossing.

49

Figure 5.3.4

6″ Steel conduit disconnect from pulling head at Kajla river

50

Figure 5.3.5

Bore hole Cross Section at Kajla river crossing

50

Figure 5.4.1

30″ Pipe string preparation on Asharier river water

52

Figure 5.4.2

Pipe string of Meghna river floated on Asharier river

53

Figure 5.4.3

Pipe site preparation for pipe pullback at Meghna pipe site

54

Figure 5.4.4

Rig machine (GD-3500L) installed for Meghna river crossing

55

Figure 5.4.5

Rig anchorage arrangement (Plan View)

56

Figure 5.4.6

Forward reaming for Meghna river

57

Figure 5.4.7

Product pipe attached with pulling assembly and water filling arrangement for buoyancy control.

58

Figure 5.4.8

Mud pump breakdown at Meghna rig site

59

Figure 5.4.9

Pipe pullback completion of Meghna river crossing

60

Figure 5.5.1

Layout of Asharier river crossing site

61

Figure 5.5.2

Rig unit mobilization by barge at Asharier river rig site

63

Figure 5.6.1

Pipe site layout of Meghna-Gumoti river crossing

64

Figure 5.6.2

Rig anchoring arrangement at Meghna-Gumoti river crossing site

65

Figure 5.6.3

Rig anchoring arrangement by driven 6m long steel sheet pile

66

Figure 5.6.4

16″ Casing pipe arrangement.

67

Figure 5.6.5

Fly cutter and barrel type reamer assembly for 24″reaming

68

Figure 5.6.6

Drill pipe recovery procedure by vibrating hammer at MeghnaGumoti river exit site

68

Figure 5.6.7

Reaming operation with two rigs on both sides of the river

69

Figure 5.6.8

Donut wiper

70

Figure 5.6.9

Water filling arrangement for buoyancy control at MeghnaGumoti river exit site Page | 14

71

Page No. Figure 5.6.10

HDD productivity factors

77

Page | 15

NOMENCLATURE ASTM

American Standard and Testing Materials

BHA

Bottom Hole Assembly

BPDB

Bangladesh Power Development Board

BRTC

Bureau of Research Testing & Consultation

CAPP

Canadian Association of Petroleum Producers.

CCPP

Combine Cycle Power Plant

CO

Carbon Monoxide

DCCA

Directional Crossing Contractors Associations

DO

Dissolve Oxygen

DoE

Department of Environment

DPP

Development Project Proforma/Proposal.

EGCB

Electricity Generation Company of Bangladesh

FBE

Fusion Bond Epoxy

GoB

Government of Bangladesh

GTCL

Gas Transmission Company Limited

HDD

Horizontal Directional Drilling

hp

Horse Power

ID

Internal Diameter

JTU

Jackson Turbidity Unit

km

Kilo Meter

lb

Pound

MDL

Minimum Detection Limit

MMscfd

Million cubic feet per day at standard condition.

MT

Metric Ton

MLV

Main Line Valve

MW

Mega Watt

NOx

Oxide Nitrogen

OD

Outer Diameter. Page | 16

Petrobangla

Bangladesh Oil, Gas & Mineral Corporation.

PPM

Parts Per Million

ROW

Right-of-Way

RPM

Round per Minuit

RDDP

Revised Development Project Proforma/Proposal

SPM

Suspended particulate Maters

SO2

Sulphur dioxide

WB

World Bank

WT

Wall Thickness.

3LPE

Three Layer Polyethylene

Page | 17

CHAPTER-1 INTRODUCTION _____________________________________________________________________________________ __

Watercourse crossing is a unique component of pipeline construction projects. Watercourse crossing construction typically requires devoted crews and specialized equipment, specific engineering design and specific planning and regulatory approval considerations. Crossings pose unique risks to the success of pipeline projects.

Pipelines are used for a number of purposes. These include e.g.: 1. Export (transportation) pipelines. 2. Flow lines to transfer product (gas, Oil, Water). 3. Water injection or chemical injection flow lines. 4. Flow lines to transfer product between platforms, subsea manifolds and satellite wells. 5. Electric/Optical Fiber cable /Telecommunication line passing through pipeline under the water body/river.

Pipeline water courses crossing construction have several techniques commonly used. Now a daywide water courses crossing by trenchless technology is popular due to less affected existing facilities. Horizontal directional drilling (HDD) method is a prime example of the application new technologies in environmental practice for pipeline crossing the river. HDD is a relatively new construction method, but its use has been growing dramatically from 1990s. HDD refers to method in which a borehole is advanced other than vertically, and curves prior reaching a target zone. The drilling rate and direction are both variable and controllable during boring operations. Typically included are a wide range of horizontal and angled petroleum exploration and geotechnical drilling application like pipeline, utilities, oil and gas production etc.[1]

HDD has emerged as a preferred crossing method in many situations for the installation of oil and gas pipelines as well as other utilities under watercourses, roads, rail lines, steep slopes and other obstacles. This technology has been enthusiastically embraced by proponents, contractors and regulators as a potentially low impact construction technique. Page | 18

In many cases, however, the suitability of the HDD method must be evaluated and compared to more traditional open-trench construction techniques in order to ensure that an appropriate technique is chosen for the conditions and concerns present at a particular crossing. Recognition of the advantages, limitations and potential risks of HDD is an important step in this evaluation.

The successful design and construction of an HDD is the result of a team effort combining the skills of the regulatory group, owner, engineering consultant, environmental consultant, inspection services and the specialist HDD contractor. Success in this endeavor is measured in more than the successful pull back of the pre-built pipeline drag section. It is important to realize that an HDD may represent the critical path on the overall project schedule. In addition, an HDD may have the highest risk of failure of any activities on a project. Therefore, all aspects of planning and design for an HDD need to be assigned a high priority or importance value due to their potential effect on the overall the HDD project. Bangladesh government has policy and plan,Government’s development goals are[2] 1. To provide energy for sustainable economic growth and for maintaining energy security in the country 2. To provide energy to all socio-economic groups in the country especially to the lessdeveloped areas 3. To diversify use of indigenous energy and 4. To contribute towards protection of the environment

In order to achieve the above goals, the Government is planning to take various measures for the petrochemical fuel sector including natural gas such as to increase the proven gas reserves by hastening survey and gas transmission network. From that point of view, Government took steps to supply and distribute gas to the existing and upcoming power plant in eastern side of Dhaka i.e. Meghnaghat, Haripur and Siddhirganj areaunder Narayanganj district by constructing a 60kmX30″ gas transmission pipeline from Bakhrabad gas field, Comilla to Siddhirganj power plant, Narayanganj. This pipeline project“60kmX30″ Bakhrabad-Siddhirganj gas transmission pipeline project” implemented by a state own organization “Gas Transmission Company Limited (GTCL)” under Petrobangla. [3]

In this study, present challenges and mitigation of challenges are conducted about the gas pipeline crossing the river by HDD methods. The said pipeline project has six numbers of river Page | 19

crossings named as Shitallakhya river,Old Brahmaputra river, Kajla river, Meghna river, Asharier river and Meghna-Gumoti river. During river crossing, different types of challenges are found such as ROW mismatch, higher entry & exit angle, non-availability of straight ROW for pipe string preparation, wrongly selection of reamer combination, difficulties of mud disposal, magnetic interference problem and breakdown of equipment/machinery etc. that was mitigated by varieties type of technical solutions which is explained in the following chapters.

1.1 OBJECTIVE The study has been undertaken with following objectives; 1. To analyze the problems encountered and remedial measures taken while river crossing work is continue. 2. To categorize these problem in different way such as the frequency of occurrence, degree of difficulty, monetary involvement etc. 3. To identify the factors affecting the pipeline construction crossing river by HDD method. 4. To reveal different accidents and assessing environment related issues in pipeline construction project.

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CHAPTER-2 HORIZONTAL DIRECTIONAL DRILLING (HDD) _____________________________________________________________________________________ __

Before 1445, Leonardo da Vinci invents and constructs the first horizontal drilling machine above ground. It serves to bore wooden logs to produce wooden water pipes. In his lifetime, ten horizontal drilling machines are presumed to have been built.Leonardo da Vinci also improves the mechanism of vertical drilling. In 1987 First HDD applications start in England. In 2004 Largest HDD unit in Europe is built in Wenden near Olpe (450-ton unit by Prime Drilling). [4]

2.1

IMPORTANCE OF TRENCHLESS TECHNOLOGY

Buried pipelines provide essential services for urban areas. These services include distribution of drinking water and natural gas, oil transport, transmission of waste water for treatment, storm sewers for flood prevention, power and telecommunication conduits, and transportation tunnels. There has been an increasing demand on these services due to increased population, growing business, and industries. This requires upgrades to the capacity of existing utilities either by upsizing or by installing new utilities.

Open-trench methods for installing new buried pipes or replacing existing pipes involve excavating a trench, removing the old pipe (for replacement methods), preparing the bedding for the new pipes, placing the new pipe, and backfilling with compaction. These methods have disadvantages including higher cost and construction times, problems with groundwatercontrol, safety risks, environmental effects, and business interruption. In cases like installation of a pipe below a water body, the open trench method is not an option. [1]

Trenchless methods, which have been progressing rapidly in the last few decades, provide efficient alternatives that overcome most or all of these challenges; 1. They are usually less expensive and faster to conduct 2. They reduce or eliminate the traffic congestion that lead to business interruption and higher exhaust emission 3. They pose lower safety risks to construction workers and the public and less influence on the environment Page | 21

4. They prevent long excavations, which cause inconvenience and unpleasant views for the nearby residents and disturbancee to other infrastructure (pavement, pipes and buildings) 5. They can reduce disturbanc

Moreover, trenchless techniques are often the only option in congested urban centersand open-cut environmentally sensitive areas, where open cut installation methods are not allowed. The objective of this chapter is to provide background information on horizontal directional drilling operations, and to introduce the research methodology and procedures.

2.2

HDD OBJECTIVES AND METHODOLOG

All the tasks associated with the HDD project are as shown in Figure 2.1.

Figure 2.1: Tasks associated with HDD project [5] Briefly, HDD is a steerable trenchless method of installing underground pipes, conduits and cables in a shallow arc along a prescribed bore path by using a surface launched drilling rig, surface-launched area. The with minimal impact on the surrounding are he HDD process begins with boring a small,

horizontal hole (pilot hole) under the crossing obstacle (e.g. a highway, railway, river crossing etc.) with a continuous string of steel drill rod. When the bore head and rod emerge on the opposite side of the crossing, a special cutter, called a back reamer, is attached and pulled back through the pilot hole. The reamer bores out the pilot hole so that the pipe can be pulled through. The pipe is usually pulled through from the side of the crossing opposite the drill rig.Theobjectives and methodologies of HDD process areexplained step by step in the following paragraphs.

2.2.1 Pipe String Preparation The pipeline should be welded and pretested in a single string in the alignment of the proposed crossing. The risk of getting stuck during pullback is increased by standby in the pulling operation, whether it is because of a mechanical problem or a tie-in of two sections. A typical pipe string at drill exit site is shown in Figure 2.2.

1. Pipe end for catenary calculation

5. Pulling assembly (pull head, swivel, reamer or bullet nose)

2 .Crane /Side boom and cradle number 1

6. Pipeline rollers

3 .Crane /Side boom and cradle number 2

7.Force at pipe end (friction on remaining rollers)

4. Crane /Side boom and cradle number 3

8. Pulling force 9.Weight of pulling assembly

Figure 2.2: Pipestring preparation.[6] 2.2.2

Rig Set Up

A horizontal drilling rig and its ancillary equipment typically require a temporary workspace of approximately 150 feet (45 m) by 250 feet (75 m). The addition of water storage may increase this area. A typical horizontal drilling spread can be moved onto the site in approximately 10 tractor loads. Where marine access is available, barges can be used for site access, to move and storedrilling fluids, and to augment land based workspace. Equipment typically found on the rig site/drill entry side of a HDD isas show in Figure2.3.

Page | 23

Figure2.3: Rig site work space.[6]

Rig set up at any entry point a steel frame footing or “Dead Man” will be buried to which the drill rig will be secured onto. This will prevent any movement of the drill rig during drilling operation. After successful set up of rig unit, Bottom Hole Assembly (BHA) and drill bit connected.

2.2.3

Pilot Hole

Pilot hole directional capability is accomplished by using a non-rotating drill string with an asymmetrical leading edge. A steering bias is created by the asymmetry of the leading edge. If a change in direction is required, the drill string is rolled so that the direction of bias is the same as the desired change in direction. Drilling progress is normally achieved by hydraulic cutting action with a jet nozzle.

Mechanical cutting action, when required, is provided by a downhole positive displacement mud motor. The actual path of the pilot hole is monitored during drilling by taking periodic readings of the inclination and azimuth of the leading edge.

These readings, in conjunction with

measurements of the distance drilled since the last survey, are used to calculate the horizontal and vertical coordinates along the pilot hole relative to the initial entry point on the surface is shown in Figure 2.4. Page | 24

Figure 2.4: Pilot hole drilling procedure. [12]

In some cases, a larger diameter wash pipe may be rotated concentrically over the nonrotating drill string. This serves to prevent sticking of the non-rotating string and allows its drilling bias to be freely oriented. It also maintains the pilot hole if it becomes necessary to withdraw the steerable string.

When the steerable string penetrates the surface at the exit point opposite the horizontal

drill rig, the pilot hole is complete.

2.2.4 Pilot Hole Reaming Enlarging the pilot hole is accomplished using either pre reaming passes prior to pull back or simultaneously during pull back. Pre reaming tools are typically attached to the drill pipe at the exit point. The reamers are then rotated and drawn to the drilling rig thus enlarging the pilot hole is shown in Figure 2.5.

Figure 2.5: Reaming Procedure.[12]

Drill pipe is added behind the reamers as they progress toward the drill rig. This insures that a string of pipe is always maintained in the drilled hole. It is also possible to ream away from the drill rig. In this case, reamers fitted into the drill string at the rig are rotated and thrust away from it. Reaming tools typically consist of a circular array of cutters and drilling fluid jets. Page | 25

Drilling fluid is pumped through the reamers to aid in cutting, support the reamed hole, and lubricate the trailing pipe. For smaller diameter lines in soft soils, pre reaming passes may be omitted and the final installation pass is undertaken upon completion of the pilot hole. [6]

2.2.5

Swab Pass

While pilling the reamer back to the Rig, it is feels that the hole is not conditioned or if there is a collapse of hole, additional swab passes shall be made. High yield bentonite with quick jelling characteristics shall be used to preserve the integrity of the borehole during the swab pass.

2.2.6 Product Pipe Attachment and Preparations for Pipe Pullback On a pre-welded and tested product pipe string have been attached a pulling head. The section of the product pipe string has been lifted with the help of adequate lifting equipment (Side Booms) to make a necessary over bend. The pipe string behind the over bend has been placed on the roller on natural ground surface as shown in Figure 2.6&2.7.

Figure 2.6: Details of Pipe Roller.[7]

Figure 2.7: Pipe String lifted on roller by lifting apparatus (Side Boom). [7]

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Once the over bend section of the product pipe string is properly supported, pipe pulling head attached with pulling assembly. The all activities of pipe site/ drill exit site are as shown in Figure 2.8.

1.

Mud pit

2.

Exit Pit

3.

Rollers

4.

Pipe String/Product Pipe

5.

Excavator

6.

Drill Pipe Rack

7.

Generator

8.

Transport to Recycling Unit.

Figure 2.8: Typical HDD Site Layout Pipe Site. [6]

2.2.7 Buoyancy Control In any directionally drilled crossing, one of the main considerations of the pipe pull back is the weight of the pipe in the pathway and the associated force necessary to overcome this resistance, Obviously, the heavier the pipeline, the more difficult the operation.When installing largediameter pipelines, the buoyancy of the pipe in the fluid creates more resistance than the gravitational weight of the pipe. To successfully install large-diameter pipelines, it must be consider the weight and buoyancy of the pipe. If the pipe is too buoyant, consider adding weight to the pipe. The preferred method for combating buoyancy is to add water into large-diameter pipelines during the pullback operation. The simplest method is to pump water directly into the pipe through a filler line or pipe.

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This water is pumped into the pipeline as it goes below the ground surface without adding weight to the pipe on the surface are as shown in Figure 2.9.

1 Pipeline string

4 Mud pit

7 Water hose reel for ballasting (if required)

2 Pipeline rollers

5 Mud pit (dirty mud)

8 Water pump for ballasting (if required)

3 Entry pit

6 Pipeline handling cranes with cradles

9 Hose from water source

Figure 2.9: Typical pipe side layout with buoyancy control arrangement.[6] 2.2.8

Pipe Pullback

In this case, the prefabricated pipeline pull section, or sections, is attached behind the reaming assembly instead of more drill pipe and follows the reamers to the drill rig. A swivel is utilized to connect the pull section to the leading reamers to minimize torsion transmitted to the pipeline.[6] The following Figure showed the pullback procedure.

Figure no. 2.10: Pipe pullback procedure.[12] Page | 28

2.3

BRIEF DESCRIPTION OF HDD EQUIPMENT/ACCESSORIES

2.3.1

Rig Unit

A basic horizontal directional rig is illustrated in Figure 2.11.

Figure .2.11: Typical rig unit Drill rig are available in a range of size and are distinguished chiefly by the torque and push/pull force they provide. The drill rig provides thrust to the drilling tool and pullback to the drill string. When drilling a directional bore hole, the drill string is rarely in a vertical position and therefore the weight of the bit or thrust on the drill string must be provided by the drill rig. The force on the bit is provided (through the drill pipe) a chain or rack-and pinion system on the rig. [5]

The classification and characteristics of HDD rigs are explain in tabular form in following

Table 2.1 Table 2.1 Classification and characteristics of HDD rigs.[8] Small/Mini Rig

Medium/Midi Rig

Large/Maxi Rig

Thrust/Pullback force

100,000lbs

Maximum Torque

20,000 ft-lbs

Rotational Speed

>130rpm

90-210rpm