Annular Space Report

8/10/2019 Annular Space Report

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EVALUATION OF THE ANNULAR SPACE REGION IN

HORIZONTAL DIRECTIONAL DRILLING INSTALLATIONS

Prepared by

Samuel T. Ariaratnam, Ph.D., P.Eng.Arizona State University

2001


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TABLE OF CONTENTS

ABSTRACT...........................................................................................................5

CHAPTER ONE INTRODUCTION TO HDD.............................................61.1 INTRODUCTION ......................................................................................................... 61.2 THE HDD INSTALLATION PROCESS...................................................................... 8

CHAPTER TWO DRILLING FLUIDS IN HDD.........................................102.1 INTRODUCTION TO DRILLING FLUIDS AND ADDITIVES.............................. 102.2 GENERAL DRILLING FLUID FUNCTIONS AND PROPERTIES........................ 15

CHAPTER THREE FIELD EVALUATION................................................203.1 INTRODUCTION ....................................................................................................... 20

3.1.1 University of Alberta Farms, Edmonton, Alberta................................................................203.1.2 Sil Silica Sand Pit, Bruderheim, Alberta.................................................................................21

3.2 FIELD SETUP.............................................................................................................. 223.3 INSTALLATION PROCESS........................................................................................ 233.4 POST-INSTALLATION............................................................................................... 243.6 DRILLING FLUID FIELD TESTS............................................................................. 273.7 CLAY SITE ANALYSIS............................................................................................... 30

CHAPTER FOUR CONCLUSIONS.............................................................464.1 INTRODUCTION ....................................................................................................... 464.2 RECOMMENDATION FOR FUTURE RESEARCH................................................. 48

CHAPTER FIVE - REFERENCES..................................................................49


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LIST OF FIGURES

FIGURE 1-1. Horizontal Directional Drill Rig .............................................................................. 7FIGURE 1-2. Product Installation Phase ........................................................................................ 9

FIGURE 2-1. Schematic of Bentonite Clay Particles.................................................................. 10

FIGURE 3-1. University of Alberta Farms Site (Clay Soil Medium).......................................... 21FIGURE 3-2. Sil Silica Sand Pit (Sand Soil Medium) ................................................................ 22

FIGURE 3-3. Typical Field Setup ................................................................................................ 23

FIGURE 3-4. Fluted Reamer Installing 100mm (4 in.) HDPE Pipe ............................................ 24FIGURE 3-5. Saw Cut to Expose Open Cross-Section ................................................................ 25

FIGURE 3-6. Field Mud Testing Kit ............................................................................................ 28

FIGURE 3-9. 100mm (4 in.) Clay Excavation @ 1 week ............................................................ 32FIGURE 3-10. 200mm (8 in.) Clay Excavation @ 1 week .......................................................... 32

FIGURE 3-11. 300mm (12 in.) Clay Excavation @ 1 week ........................................................ 32

FIGURE 3-12. 100mm (4 in.) Clay Excavation @ 2 weeks......................................................... 33

FIGURE 3-13. 200mm (8 in.) Clay Excavation @ 2 weeks......................................................... 33

FIGURE 3-14. 300mm (12 in.) Clay Excavation @ 2 weeks....................................................... 33FIGURE 3-15. 100mm (4 in.) Clay Excavation @ 4 weeks......................................................... 34

FIGURE 3-16. 200mm (8 in.) Clay Excavation @ 4 weeks......................................................... 34FIGURE 3-17. 300mm (12 in.) Clay Excavation @ 4 weeks....................................................... 34

FIGURE 3-18. 100mm (4 in.) Clay Excavation @ 1 year............................................................ 35

FIGURE 3-19. 200mm (8 in.) Clay Excavation @ 1 year............................................................ 35FIGURE 3-20. 300mm (12 in.)Clay Excavation @ 1 year........................................................... 35

FIGURE 3-21. 100mm (4 in.) Sand Excavation @ 1 day ............................................................ 38

FIGURE 3-22. 200mm (8 in.) Sand Excavation @ 1 day ............................................................ 38

FIGURE 3-23. 100mm (4 in.) Sand Excavation @ 1 week.......................................................... 39FIGURE 3-24. 200mm (8 in.) Sand Excavation @ 1 week.......................................................... 39

FIGURE 3-25. 300mm (12 in.) Sand Excavation @ 1 week........................................................ 39FIGURE 3-26. 100mm (4 in.) Sand Excavation @ 2 weeks ........................................................ 40FIGURE 3-27. 200mm (8 in.) Sand Excavation @ 2 weeks ........................................................ 40

FIGURE 3-28. 300mm (12 in.) Sand Excavation @ 2 weeks ...................................................... 40

FIGURE 3-29. 100mm (4 in.) Sand Excavation @ 4 weeks ........................................................ 41FIGURE 3-30. 200mm (8 in.) Sand Excavation @ 4 weeks ........................................................ 41

FIGURE 3-31. 300mm (12 in.) Sand Excavation @ 4 weeks ...................................................... 41

FIGURE 3-32. 100mm (4 in.) Sand Excavation @ 1 year ........................................................... 42FIGURE 3-33. 200mm (8 in.) Sand Excavation @ 1 year ........................................................... 42

FIGURE 3-34. 300mm (12 in.) Sand Excavation @ 1 year ......................................................... 42

FIGURE 3-35. Pocket Penetrometer............................................................................................. 43

FIGURE 3-36. Field Measurements using Pocket Penetrometer ................................................. 44FIGURE 3-37. Unconfined Shear Strength of Annular Space Over Time................................... 45


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LIST OF TABLES

TABLE 2-1. Composition of Drilling Fluids used in Research Project........................................... 19TABLE 3-1. Field Test Drilling Fluid Properties............................................................................ 29


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ABSTRACT

Recently, questions concerning the compactive nature of drilling fluids within the annular space

during Horizontal Directional Drilling (HDD) operations have arisen. To address these concerns, a

field and laboratory study was conducted to provide both a qualitative and a quantitative assessment

of the annular space. The study consisted of installing 61 m (200 ft.) bore lengths of 100 mm (4 in.),

200 mm (in.), and 300 mm (12 in.) SDR 17 High Density Polyethylene (HDPE) pipe in two

different soil mediums: clay and sand. Subsequently, the pipes were excavated with visual and

strength measures of each of the installations taken at time periods of 1 day, 1 week, 2 weeks, 4

weeks, and 1 year after installation to assess the annular space region over time. Additionally,

samples of the drilling fluid were evaluated both in the field and at a laboratory. This paper presents

the results of this research initiative and provides qualitative and quantitative information on

borehole annular space integrity during HDD installations. The study revealed that: 1) the integrity

of the annular space was maintained, as little evidence of voids was present; and 2) the strength

properties increased over time through apparent consolidation, or equalization, with the native soil.

For Additional Information Contact:

Dr. Samuel T. Ariaratnam

Associate ProfessorDel E. Webb School of ConstructionArizona State UniversityTempe, Arizona 85287-0204tel. (480) 965-7399; fax (480) 965-4708Email: [email protected]


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CHAPTER ONE INTRODUCTION TO HDD

1.1 INTRODUCTION

New underground infrastructure construction is an important aspect for a developing municipal

environment. Installing this new infrastructure using traditional trenching techniques, particularly

open cut construction, can equate to high social costs. These social costs include noise pollution,

traffic disruption, aesthetic factors, and negative public perception. The use of trenchless

technologies can enable installation of pipelines and other conduits under these sensitive areas while

providing minimal disruption in comparison to traditional trenching methods.

Horizontal Directional Drilling (HDD) is a trenchless technology that has the capacity to

install a wide variety of pipe materials into the ground. This process provides an alternative over the

traditional open cut methodology while providing a number of benefits. For example, the HDD

process can decrease the social costs of installing underground conduit as the operation can be

performed more quickly, require less working space, and can be conducted without disruption to

surface activities (traffic and pedestrian areas). When utilized under a watercourse, the HDD

method can provide reduced environmental impacts and increased productivity in comparison to an

open cut operation (Allouche et al. 2000).

Today, Horizontal Directional Drilling (HDD) is one of the fastest growing trenchless

construction methods. Currently, there are over 10,000 HDD rigs in operation throughout the

world (Krzys 1999). Smaller drilling rigs (Figure 1-1) are typically used for the installation of

telecommunication residential service cables. Larger rigs are capable of installing pipelines up to

1200 mm (48 in.). With this growth comes an ever-increasing need for gaining a better

understanding of the physical nature of this construction process and its influence on the


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surrounding medium. While HDD has been employed in North America since the 1970s, there are

still some municipalities and regulatory bodies that are wary of allowing the process due to negative

perceptions regarding the annular space region. It is hoped that the results of this research will

make these municipalities and regulatory agencies more aware of the capabilities of the HDD

process and curb any concerns regarding the effects on the annular space created during these

operations. Thus, these bodies can consider the use of HDD for new infrastructure development

programs.

FIGURE 1-1. Horizontal Directional Drill Rig

During the summer of 2000, a field research program was conducted in which six HDD

installations were performed at two different locations. The first series of installations were


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conducted in June 2000 at the University of Alberta Farms in Edmonton, Alberta, in a clay soil

medium. At this location, three SDR 17 High Density Polyethylene (HDPE) pipes were installed;

one each of 100 mm (4 in.), 200 mm (8 in.), and 300 mm (12 in.) diameters. The second series of

installations was conducted in July 2000 at the Sil Silica sand pit located west of Bruderheim,

Alberta. At this sand location, three SDR 17 HDPE pipes were installed; one each of 100 mm (4

in.), 200 mm (8 in.), and 300 mm (12 in.) diameters. All of these installations were 61 m (200 ft) in

length and the depth of each installation was based on pipe diameter; 600 mm (2 ft) for the 100 mm

(4 in.) diameter pipes, 900 mm (3 ft) for the 200 mm (8 in.) diameter pipes, and 1200 mm (4 ft) for

the 305 mm (12 in.) diameter pipes.

1.2 THE HDD INSTALLATION PROCESS

Horizontal Directional Drilling (HDD) is a trenchless method of pipe installation. As a trenchless

construction method, there are minimum, if any, excavation requirements to install pipe and conduit

of varying size and depth. This technique allows for great design flexibility as installation paths, or

borepaths, may be curved or straight, with the path changing direction and depth to avoid

subsurface obstacles.

The installation of pipe and conduit utilizing directional drilling is typically completed in a

two-phase operation including the drilling of a pilot hole and its subsequent reaming to install the

product pipe. Installation of conduit and pipe is conducted from the surface, and commences with

the boring of a pilot bore along the path of installation. The pilot bore is launched from the surface

at an angle between 8 and 20 degrees to the horizontal, and then gradually becomes horizontal when

the required depth is reached. The bore can be steered and tracked from the surface using a walk

over or wire line locator system to direct the bore to the exit location (Ariaratnam and Allouche

2000). Once the drill string reaches the surface at the exit location, a reamer is attached to the drill


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CHAPTER TWO DRILLING FLUIDS IN HDD

2.1 INTRODUCTION TO DRILLING FLUIDS AND ADDITIVES

Drilling fluid is composed of a carrier fluid (water) and drilling fluid additives (bentonite and/or

polymers). Bentonite is a naturally occurring clay mineral (montmorillinite) that forms a mud when

mixed with water. When bentonite is mined, the clay platelets (flat plate-like particles), which have

been subjected to high confining stresses, are closely compressed and have very little water between

them. An aggregate is a unit of stacked clay platelets. When water enters between some of the clay

platelets, it immediately causes them to disperse, separating the clay platelets as illustrated in Figure

2-1. The dispersion is aided by shearing through good quality mixing equipment. In fact, one cubic

inch of bentonite, if mixed until it is broken down to single platelets, would have enough surface

area to cover 66 football fields.

FIGURE 2-1. Schematic of Bentonite Clay Particles


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circulation once the drilling fluid or slurry has set for a period of time. This higher gel will

result in higher initial pressures needed to get this drilling fluid or slurry to move (less shear

thinning). If this pressure is greater than the pressure required to cause hydrofracture,

circulation loss or frac-out may occur. Adequate gel strength must be maintained to suspend

drilled solids when the fluid is in the static state for the formation being drilled. The drilling

fluid must suspend the solids and keep them in suspension as they are transported out of the

bore. The resulting slurry (fluid and solids) acts like a conveyor belt to remove at least

enough solids to make room for the product. Gel strength is especially important in coarse-

grained soils, and can be important in clays and shales, especially when using large diameter

reamers, which tend to produce large cuttings. The solids will only remain in suspension in

the slurry if the gel strength is adequate.

Fluid Loss and Fluid Density. Fluid loss is the measurement of filtrate (free water)

passing from the drilling fluid into a porous permeable formation. It is not to be confused

with whole mud loss to the formation (loss circulation). Fluid loss properties are measured

using a standard filter press. A sample of the fluid to be tested is placed in a metal cell and

pressurized (100 psi) for 7.5 minutes. The filtrate that is collected from the filter press in a

graduated cylinder is measured in cubic centimeters (cc). This filtrate quantity is multiplied

by 2 and represents fluid loss. Suspended particles in the drilling fluid will be deposited on

the side of the bore hole or in the case of a fluid loss test on a piece of filter paper. This

filter cake represents the thickness, durability, quality, and slickness of the filter cake. A slick

tough durable filter cake can and often will only be 2/32-inches thick when checking a clean

fluid. With experience, it is also an indicator as to the borehole integrity. High fluid loss

properties represent a thicker softer filter cake. This thicker filter cake decreases the annular


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space in the borehole, thus requiring greater pressure due to drilling fluid and cuttings

traveling in the smaller passage way. The filtrate passing into the formation can also cause

weakening of the formation to the point of collapse. Low fluid loss is an indicator as to the

inhibiting properties of that fluid for clays and shale drilling. Low fluid loss is the key to

borehole integrity. Fluid density is the weight of a gallon of drilling fluid. The density or

mud weight of a fluid is measured using a mud balance. A gallon of water weighs 8.34 lbs.;

any additional weight in this water will come from active or inactive solids. A typical mud

weight for a clean bentonite-polymer HDD drilling fluid will be around 8.5 lbs per gallon or

3% solids by weight. Any additional weight to this fluid above 8.5 lbs per gallon is due to

active or inactive solids from the formation. To convert the density of the fluid or slurry to

solids content, the following equation can be used: (Density - 8.34) X 8 = % solids, where

density is in lbs/gallon. This calculation assumes a specific gravity of solids of 2.5. The fluid

density value can be used in two ways. First, it can be used to determine if the solids content

is approaching unacceptable levels (9 lbs/ gallon for small to medium rigs and 10 lbs/gallon

for large rigs). However, the unacceptable level will vary with ground conditions, disposal

requirements, and pumps. These solids, if allowed to build up in the fluid system, can have a

very negative effect on the efficiency of the total drilling system, from breaking the

backbone of the drilling fluid to excessive wear on pumps. If this occurs, the solids content

must be reduced by: 1) additional cleaning (i.e. finer screens, re-circulation within the

cleaning system); 2) reducing drilling penetration rates; and 3) disposing and mixing new

fluids. Secondly, fluid density can be used to measure the effectiveness of solids control

equipment when using a recycling system.


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groundwater) from flowing into the bore or drilling fluids from exiting the bore into the

formation (loss of circulation).

Providing hydraulic power to downhole mud motors.

When the drilling fluid is pumped into the hole, the fluid, just like water, attempts to flow

through the sand or gravel. However, the bentonite platelets will start to plaster or shingle off the

wall of the borehole and form a filter cake that seals off the flow of fluid from the bore into the

native soil. The ideal filter cake is slick and tough, forms quickly during construction of the

borehole, reduces migration of drilling fluid into the formation, and reduces intrusion of ground

water and soil into the bore. Optimum filter cake thickness should range between 1/32 and 3/32 in.

The water that does manage to filter through the cake is referred to as the filtrate. Filter

cake quality can be improved to reduce the amount of filtrate entering the surrounding soil. This

can be accomplished by one of two methods: 1) adding more bentonite (more platelets); or 2) using

certain polymers in conjunction with bentonite to tighten the filter cake. It is more effective to use a

bentonite/polymer mix because it is less viscous, more pumpable, and flowability in the annular

space will be maximized due to the shear-reducing properties of the fluid (i.e. more slurry will flow).

In addition to providing a filter cake layer, the drilling fluid must provide suspension

characteristics or gel strength. The drilling fluid has to be able to support, suspend and carry the

cuttings. If the fluid cannot suspend the drilled material, that material will quickly settle out of

suspension and pack around the drill pipe or around the product line being pulled. Even if the fluid

has a high viscosity (i.e. thick fluid) it may have very low carrying capacity (i.e. gel strength). Proper

control of gel strengths is an important factor in avoiding excessive downhole pressures. Gel

strength is usually checked with a clean fluid. When solids are added to this fluid, the drilling fluid

properties change drastically. The yield value of a drilling fluid (not the gel strength) is the


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measurement of the drilling fluids internal resistance to flow and thus the carrying capacity of the

fluid when it is moving. Gel strength and yield value are more important in horizontal drilling than

viscosity. Because plain water has low viscosity and no gel strength or yield. Polymers by

themselves have high viscosity but low gel strength and yield. Therefore, bentonite is required to

provide the necessary carrying capacity for cuttings from coarse soils.

At times, additives such as detergents are added to the drilling fluids to counteract some of

the formation characteristics such as swelling and stickiness. Other additives are used to adjust the

pH of the fresh water constituent of drilling fluid.

For HDD, the proper drilling fluid mixture is heavily dependent upon the soil encountered.

It must be formulated for the anticipated geological conditions. For simplicity, soil conditions may

be defined as either a coarse soil (sand and gravel) or a fine soil (clay, silt and shale). When drilling

through sand and gravel, a drilling fluid needs to serve two important functions: stabilization of the

borehole and suspension and transportation of cuttings. When drilling through clay, the same

functions need to be performed; however, an additional requirement of the fluid is to retard swelling

and reduce sticking of the soil to the downhole tooling and product line being installed. Geological

conditions may vary between fine and coarse soils; consequently different combinations of drilling

fluid additives will be needed to perform the required functions under actual conditions. In general,

for coarse soils bentonite should be used, while for fine soils polymers (possibly added to a

bentonite base) are recommended. When drilling through sands and gravel, drilling fluids may

migrate out of the bore into the native soil formation. Bentonite and lost circulation materials

reduce fluid losses into the formation.

To create the optimal drilling fluid, each one of the above factors must be considered.

Undoubtedly, the native soil will decide first and foremost what type of drilling fluid is required.


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Once the native soil is properly identified, the right type of drilling fluid can be chosen and then

quantified for optimal performance.

2.3 DRILLING FLUID COMPOSITION

The drilling fluid mixtures that were utilized during the installations in this research are presented in

Table 3-1. A representative from Baroid Industrial Drilling Products (IDP), who was present during

all stages of each installation, conducted all of the drilling fluid designs. Additionally, all of the

drilling fluid was supplied by Baroid IDP. For each batch, a cup of soda ash (approximately 1 lb.)

was also added into the mixture to ensure that the pH of the make up water remained at an optimal

level of 8 to 10. At this level, the Bore-Gelreacts better with the make up water and the overall

drilling fluid is able to optimally perform its necessary functions. Bore-Gelwas the primary

component, along with water, that was utilized for the installations. Bore-Gelis comprised mainly

of sodium bentonite, which provides the primary function of stabilizing the borehole and removing

the cuttings. EZ-Mudis a liquid polymer that is used as a borehole stabilizer and prevents reactive

clay from swelling. Con Det is a wetting agent that aids in the cleaning of the drill bit and

counteracts the sticking tendencies of clays. No-Sagis a gel strength enhancer that enables better

suspension of cuttings and increases the carrying capacity for solids suspension. The constituents of

the drilling fluid are all products that are produced by Baroid IDP. These products (and many

others) are key components used by directional drilling contractors to maximize drilling

performance for a wide range of HDD projects.


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TABLE 2-1.Composition of Drilling Fluids used in Research Project

Pipe Designation# of

BatchesWater

Bore-

Gel

EZ-

MudCon Det Other

100mm (4) Clay 1 900gal 150lbs 2L 2L -

200mm (8) Clay 2 900gal 150lbs 2L 2L -

300mm (12) Clay 2 900gal 150lbs 4L 2L 2 lbs No-Sag

100mm (4) Sand 1 900gal 250lbs - - -

200mm (8) Sand 1 900gal 250lbs - - 2.5 lbs No-Sag

300mm (12) Sand 2 900gal 250lbs - - 5 lbs No-Sag


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CHAPTER THREE FIELD EVALUATION

3.1 INTRODUCTION

Field testing was performed at two different locations in order to evaluate the annular space region

in both a cohesive and a cohesionless soil medium. This involved the installation of 61m (200 ft.)

bore lengths of 100 mm (4), 200 mm (8), and 300 mm (12) SDR 17 High Density Polyethylene

(HDPE) pipe in two different soil mediums: clay and sand. Field locations were chosen based on

the consistency of soil conditions (i.e. homogeneous), topography of the site, and the ability to leave

the pipe in the ground for a period of one year to conduct long term analysis. The two locations

utilized for this research were the University of Alberta Farms in Edmonton, Alberta and the Sil

Silica sand pit in Bruderheim, Alberta.

3.1.1 University of Alberta Farms, Edmonton, Alberta

The University of Alberta Farm site, shown in Figure 3-1, was chosen as it provided the cohesive

soil medium for this research. The upper 4 m (12 ft.) of the soil at this site consists of uniform

lacustrine Lake Edmonton Clay with a unit weight of approximately 18 kN/m3 (Zhang 1999).

Laboratory testing of soil samples revealed a moisture content of approximately 27%. There were

three installations performed at this location including 100 mm (4 in.), 200 mm (8 in.), and 300 mm

(12 in.) diameter SDR 17 HDPE pipes, which were each installed over a distance of 61 m (200 ft.).

These installations were performed on June 13 and 14, 2000.


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FIGURE 3-2.Sil Silica Sand Pit (Sand Soil Medium)

3.2 FIELD SETUP

Field setups at both sites were performed in a similar manner as illustrated in Figure 3-3. The

overall length of each borehole and subsequent product line was approximately 61 m (200 ft).

Laterally, the pipes were spaced 5 m (15 ft.) apart from the centerline of one installation to the

centerline of the next. This 5 m (15 ft.) spacing was maintained to accommodate a surface heave

monitoring study that was being conducted simultaneously with this research program. Both sites

were surveyed prior to installation and during this time, survey stakes were placed at the beginning,

intermediate, and end points of each installation. The survey stakes were utilized to ensure that the

bore path proceeded in a straight line and were necessary for the ground surface monitoring that

was being conducted during the installation process. The placement of the drilling rig and the layout


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of the installation lines was determined by the access location for each site and to accommodate the

support equipment and product pipe being installed.

FIGURE 3-3.Typical Field Setup

3.3 INSTALLATION PROCESS

Each installation was conducted using generally accepted drilling practices to ensure that the data

collected reflected not only good drilling practice but also captured the techniques utilized by the

majority of contractors. To this extent, the contractor used fluted reamers (Figure 3-4) in both the

clay and sand soils. Reamers were sized according to the rule of thumb practice of having reamers

1.5 times the diameter of the product pipe being installed (DCCA 1998). Subsequently, on the 100

mm (4 in.) pipe installation a 150 mm (6 in.) reamer was used in a one-pass installation, a 300 mm

(12 in.) reamer was used on the 200 mm (8 in.) product pipe with a one-pass installation, and a 450

mm (18 in.) reamer on the 300 mm (12 in.) pipe with a pre-ream using the 300 mm (12 in.) reamer.

5 m (15 ft.)


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FIGURE 3-4.Fluted Reamer Installing 100mm (4 in.) HDPE Pipe

Both the clay and sand installations were excavated at sections along the borepath in

intervals of 1 day, 1 week, 2 weeks, 4 weeks, and 1 year after installation to visually assess the

integrity of the annular space. The annular space region, which is comprised of drilling fluid mixed

with native soil, is defined as the region between the outside diameter of the installed pipe and the

wall of the borehole. The analysis of the annular space region commenced once the installations of

the HDPE pipes were completed. These observations were imperative in trying to gain a better

understanding of the annular space region over time.

3.4 POST-INSTALLATION

Once the installation of a pipe is achieved, it remains untouched until the next day. Because the 100

mm (4 in.) and 200 mm (8 in.) pipes were installed in one day, they were both excavated the


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People have hypothesized about the short-term and long-term post installation state of the

annular space yet very few have actually conducted research in this area. Subsequently, this research

involved the evaluation and assessment of:

The placement of the pipe in relation to the annular space.

Any existence of voids in the annular space.

The state of the annular space in terms of strength, texture, and composition.

During the visual examination of the annular space, a geotechnical in-situ test was performed

to assess the unconfined shear strength of the annular space and native soil. It should be noted that

shear strength tests were only performed in the clay site, as this property is never evaluated in

cohesionless soils such as sand. The in-situ tests were preferred over the laboratory tests due to the

fact that a change in environmental conditions (i.e. pressure, moisture content) and the disturbance

of the samples when extracted, handled, and subsequently tested can greatly influence the test

results.

3.5 MOISTURE CONTENT

Moisture content is defined as the ratio of the weight of the water to the weight of the solid particles

in a soil medium. To obtain moisture content, the sample is first weighed and then placed in a hot

oven overnight. The next day, the dried out sample is again weighed and the moisture content is

calculated as a percentage. The moisture content in sands generally lie between 10% and 30%,

while in clay it can range from less than 5% to over 300%. The importance of moisture content in a

soil mass cannot be understated as it can have a significant effect on some of the characteristics and

behavior of a soil. For example, in fine-grained soils such as clay, high moisture content can greatly


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reduce the shear strength. At every excavation, five samples were collected from each installation to

determine moisture content of the annular space and the respective soil medium.

The moisture content of the clay averaged 27%, while the annular space averaged 38% up to

4 weeks after installation. Analysis of the annular space from the 1 year excavation revealed a

decrease in moisture content to 32%. This indicates that equalization of the annular space and the

native clay seemed to have occurred as evident by the 6% reduction in moisture content exhibited in

the annular space.

The moisture content of the sand averaged 5%, while the annular space averaged 22% up to

4 weeks after installation. Similar to the clay site, the analysis of the annular space from the 1 year

excavation revealed a decrease in moisture content to 12%. It appears that, over time, an

equalization of the annular space and the surrounding soil medium occurs, thereby increasing the

strength properties of the annular space.

3.6 DRILLING FLUID FIELD TESTS

Samples of the drilling fluid/ slurry were taken and analyzed at the same locations for each

installation as follows:

1. The first sample was taken directly out of the mixing tank. Approximately 10 minutes after all

mixtures had been added. This is denoted as theInitialsample and is a composition of only the

drilling fluid (I).

2. The second sample was taken from the entry pit approximately 3 rod lengths into the

installations. This sample is a combination of drilling fluid and the native soil (slurry) and is

denoted asReturns-EntryPit-Drilling (RED).

3. The third sample was taken from the exit pit. This is a sample of the slurry once the drill head

penetrates through the exit pit. This sample is denoted asReturns-eXit Pit-Drilling (RXD).


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4. The fourth sample was taken from the exit pit during backreaming once 5 rods were pulled in.

This sample is known asReturns-eXit Pit-Backreaming (RXB).

5. The final sample was taken just prior to the completion of the installation and is denoted as

Returns-Entry Pit-Backreaming (REB).

Each sample was analyzed using a Field Mud Testing Kit illustrated in Figure 3-6 to analyze

the properties of the drilling fluid and slurry (i.e. returns) for density, funnel viscosity, pH, sand

content, gel strength, and filtration/ filter cake.

FIGURE 3-6.Field Mud Testing Kit

A summary of the drilling fluid properties from the field test is presented in Table 3-1. The

results reveal that the density of the drilling fluid in clay remained relatively constant at an average


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value, 8.8 lbs./ gal., slightly higher than water. In sand, the average density, 12.3 lbs./ gal., was

consistently higher in the slurry samples than that of the initial samples as expected. The viscosity

increased slightly as the installations progressed with average values of 47.1 secs/qt. and 55.9 secs/qt

in clay and sand, respectively. The pH values varied between 8 and 10 for each of the sites. In clay,

the sand content was minimal, whereas consistently high readings, over 20%, were exhibited in the

sand site as expected.

TABLE 3-1.Field Test Drilling Fluid Properties

Pipe Size Soil Time Density Funnel Viscosity pH Sand Content Gel Strength Filtrate Cake Thickness

(inches) (lb/gal) (Secs/Qt) (%) (lb/100ft2) (cc/7.5min) 32nd's of an inch

4" clay 9:45(I) 8.6 39.2 10 0 0 4.8 2

4" clay 11:52(RED) 8.6 40.1 10 1.5 0 4.2 2

4" clay 1:30(RXD) 8.6 41.3 10 1 0 4.1 2

4" clay 1:45(RXB) 8.6 44.3 10 0.1 0 3.8 4

4" clay 2:10(REB) 9.6 40 8 4 0 9 8

8" clay 3:30(I) 8.6 36.3 10 0 0 4 4

8" clay 4:25(RED) 8.6 36.7 10 1 0 4.2 2

8" clay 5:07(RXD) 8.4 55.1 10 1.5 4.7 3.6 2

8" clay 5:20(RXB) 8.8 48.7 10 0 6 6.2 6

8" clay 6:00(REB) 9.5 70 10 2.5 3 4.3 4

12" clay 11:35(I) 8.6 39.9 10 0 0 4 2

12" clay 12:05(RED) 8.7 38 10 0.25 0 3.6 2

12" clay 12:50(RXD) 8.7 52.4 10 0.5 0 2.8 2

12" clay 2:05(RXB) 8.7 63.6 10 0.75 6 2.6 212" clay 3:30(REB) 8.7 60.8 10 0.75 4.5 2.6 2

4" sand 9:50(I) 8.4 46 10 0 5 4.1 2

4" sand 10:35(RED) 13.7 128 8.5 20 19 3.8 14

4" sand 12:10(RXD) 11.7 54 9 20 6.5 4 4

4" sand 12:35(RXB) 12.4 56 9 20 7.5 4.2 8

4" sand 12:55(REB) 12.9 62 9 20 7.5 4.4 8

8" sand 2:08(I) 8.45 44 10 0 0 4.8 4

8" sand 2:25(RED) 13.1 46 9 20 1.5 3.2 8

8" sand 3:40(RXD) 13.05 48 9 20 2 3 8

8" sand 4:30(RXB) 12.5 63 9 20 3 2.9 4

8" sand 5:15(REB) 12.9 68 9 20 3 3 4

12" sand 10:00(I) 8.45 31 10 0 0 4.8 2

12" sand 10:20(RED) 9.8 35 9 20 0 3.6 2

12" sand 12:55(RXD) 9.5 37 9 20 0 4 4

12" sand 4:05(RXB) 13.5 63 9 20 0 2.2 6

12" sand 5:00(REB) 12.9 58 9 20 0 2.8 8


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3.7 CLAY SITE ANALYSIS

At each cross-sectional excavation, photographs were taken to capture the insitu state of the annular

space over time. Figures 3-7 to 3-20 illustrate the annular space region of the three installed pipes at

various time intervals. As observed, the HDPE pipe is generally centered within the annular space

region with no evidence of voids. Additionally, clay, being a cohesive soil, enables the drilling fluid

to remain within the boundaries of the annular space thereby permitting the fluid to setup/solidify.

Insitu analysis of the unconfined shear strength of the drilling fluid revealed that the properties

increase over time within the annular space region. This is explained in greater detail in Section 3.9.

Comparing Figures 3-9, 3-10, and 3-11 to Figures 3-18, 3-19, and 3-20, one can see that the

visual annular space actually decreases over time and is relatively non-existent in the 1 year

excavations. It appears that, over time, the amount of water present in the annular space decreases

and the texture of the annular turns into a more solid state. This may be attributed to equalization

between the annular space region and the native soil formation. As well, there is no evidence of the

existence of voids in any of the cross-sections as confirmed by the photographs.


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FIGURE 3-7.100mm (4 in.) Clay Excavation @ 1 day

Figure 3-8.200mm (8 in.) Clay Excavation @ 1 day


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FIGURE 3-9.100mm (4 in.) Clay Excavation @ 1 week




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FIGURE 3-12.100mm (4 in.) Clay Excavation @ 2 weeks




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3.8 SAND SITE EVALUATION

For the pipe installations in sand, it was difficult to determine whether voids existed in the annular space.

Because of the disturbance created when excavating and cutting up the pipe, the slurry in the fragile and

very liquefied annular space tended to flow out of the cross-section that was just created. Once the slurry

stopped flowing and the annular space was intact, a clear and evident sign of a slight void was present in

the 100 mm (4 in.) installations as shown in Figures 3-21, 3-23, 3-26, and 3-29. In each excavation, the

voids always occurred beside the pipe and never below or above. It is difficult to assess whether these

voids existed before the cross-sections were excavated or whether they resulted from the disturbance that

was created when the cross-section was made. Some questions were answered once closer inspection of

the annular space with the void was made. When examining the void, it was evident that the void was not

local to that cross-section but in fact spread continuously through the formation. This void was

predominant found only in the 100 mm (4 in.) installation indicating that this may be an isolated incident

caused by the actual soil medium encountered. Additionally, these voids may have been formed due to

the fluid permeating into the surrounding cohesionless sand formation. The 1 year excavation of the

100 mm (4 in.) pipe, Figure 3-32, revealed no presence of voids whatsoever in the annular space.

Therefore, the presence of voids is not thought to be a problem during HDD installations in sand;

however, any short-term voids that may be presence will more than likely be eliminated through

redistribution of the soil with the annular space over time. It is important to recognize that more solids

are present in the annular space region and provide support to the installed product pipe.

Additionally, the presence of small voids are not a cause for alarm as the surrounding native soil

retains its compactive effort, which is difficult to achieve using traditional open-cut trenching

methods of pipe installation.

Figures 3-21 to 3-34illustrate the annular space region of the three installed pipes at various

time intervals. In comparison to the clay installations, the analysis revealed that the HDPE pipe

tended to settle in the upper region of the annular space. This is a result of buoyant forces acting on


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the pipe in the cohesionless sand resulting in the pipe floating upwards. In such installations,

particularly when crossing under a water coarse, it is often the practice to weigh down the pipe by

filling it with water.


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FIGURE 3-21.100mm (4 in.) Sand Excavation @ 1 day

FIGURE 3-22.200mm (8 in.) Sand Excavation @ 1 day


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FIGURE 3-23.100mm (4 in.) Sand Excavation @ 1 week




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FIGURE 3-26.100mm (4 in.) Sand Excavation @ 2 weeks




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3.9 POCKET PENETROMETER

A pocket penetrometer was used in analyzing the shear strength of the annular space. The

instrument, illustrated in Figure 3-35, is small and readily available. As well, using the penetrometer

to obtain unconfined shear strength readings (measured in kg/cm2) is relatively easy, as it entails

physically pushing the instrument into the annular space stratum to a calibration mark and recording

the subsequent reading. It should be noted that the pocket penetrometer was only utilized at the

clay site because it is only applicable in fine-grained soil. When evaluating the results of the

penetrometer tests, it is important to note that the soil is not completely uniform throughout.

Subsequently, it may exhibit different shear strength characteristics at various planes and for

different moisture contents. Therefore, it is important to note that this may or may not reflect the

true shear strength of the native soil in all directions. As well, because it is not uniform, the shear

strength characteristics through time may be influenced by the plane being sampled.

FIGURE 3-35.Pocket Penetrometer

For each cross-sectional excavation that occurred in clay, the pocket penetrometer was used

to determine the unconfined shear strength. Comparisons were subsequently made between the


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different pipe installations to assess the change in shear strength over time. The pocket

penetrometer field test was performed at various locations in the annular space surrounding each

installation, as illustrated in Figure 3-36. Figure 3-37 reveals that the unconfined shear strength of

the annular space material increases over time. For example, the initial readings for the three

installations were between 0.1 kg/ cm2and 0.25 kg/ cm2, which converged to 0.6 kg/ cm2 to 0.7

kg/ cm2recorded at the 1 year excavation. The existing clay medium exhibited unconfined shear

strengths between 0.8 and 1.1 kg/cm2from measurements taken approximately 300 mm (12) away

from the installed pipe. This increase may be explained by the consolidation of the surrounding soil

medium within the annular space over time and the slow hydration of the native clay in the slurry,

thereby increasing the strength properties around the installed pipe.

FIGURE 3-36.Field Measurements using Pocket Penetrometer


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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

24 hrs. 1 Week 2 Weeks 4 Weeks 1 Year

Time of Digup

UnconfinedShearStrength(kg/cm2)

100 mm (4 in.) 200 mm (8 in.) 300 mm (12 in.)

FIGURE 3-37.Unconfined Shear Strength of Annular Space Over Time


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CHAPTER FOUR CONCLUSIONS

4.1 INTRODUCTION

The findings of a field and laboratory study conducted to provide both a qualitative and a

quantitative assessment of the annular space region during Horizontal Directional Drilling

installations are presented. Observations of the annular space region at various time intervals after

installation indicate that small voids may initially be present in cohesionless soils due to the

permeation of fluid into the surrounding native material. However, it is important to realize that

more solids are present in the annular space region thereby providing support to the installed

product pipe. No voids were detected in any of the installations in the cohesive soil.

The shear strength of the annular space is dependent on the characteristics of the native soil

and its reaction with water. As was evident when comparing the clay and sand installations, the state

of the clay annular space was far more mature than the sand installation. It also exhibited strength

and cohesive characteristics while the annular space in sand was fluid-like. In addition, the sand

installations did exhibit initial voids, which is another sign of non-cohesion. Measures of the

unconfined shear strengths of the annular space in the clay soil medium indicate that it reaches

about 70-80% of the native soil after 1 year. This is an important consideration since these

measures are difficult to obtain using open cut methods.

Even within the same soil site, or even the same installation, there are differences between

every cross-section. Because the soil naturally exhibits different stratums or pockets of

compositions, strengths, and moisture content, the annular space reflects this as well. The annular

space was discovered to change in shape, texture, composition, shear strength, and moisture content

from cross-section to cross-section. In all cases, the diameter of the annular space region decreased


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over time to the point that it equalized (or consolidated) with the native soil. The moisture content

of the clay averaged 27%, while the annular space averaged 38% up to 4 weeks after installation.

Analysis of the annular space from the 1 year excavation revealed a decrease in moisture content to

32%. The moisture content of the sand averaged 5%, while the annular space averaged 22% up to 4

weeks after installation. Similar to the clay site, the analysis of the annular space from the 1 year

excavation revealed a decrease in moisture content to 12%. It appears that, over time, an

equalization of the annular space and the surrounding soil medium occurs, thereby increasing the

strength properties of the annular space.

The primary and most important function of the post-installation annular space is to behave

like the native soil and provide security to the installed pipe. Insitu tests and visual assessments

validate this notion, as all of the pipes that were installed remained secure with no evidence of any

potential movement. It should be noted that surface points placed along the installations revealed

that no ground settlement occurred at the surface during installation. Also, no ground settlement

was observed over time.

Much information may be obtained from field studies of construction processes such as the

research described in this report. The final results should provide owners, contractors,

manufacturers, engineers, and others interested in directional drilling with a better understanding of

the influence that HDD installations have on the surrounding medium. The six pipes installed and

the twenty-eight cross-sections that were excavated and analyzed support the opinion that the

annular space does provide the necessary attributes for the short-term and long-term success of a

pipe installation using horizontal directional drilling.


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4.2 RECOMMENDATION FOR FUTURE RESEARCH

Recommendations for future research include expanding the scope of research to include other soil

mediums, pipe diameters, and pipe material. Additionally, it would be beneficial to try assessing the

annular space using different mixtures of drilling fluid and at different depths of installation.

Evaluation of the annular space at 2 year, 3 year, etc. after installation to assess the unconfined shear

strength over a longer time horizon is recommended. This could provide additional validation of

the long-term integrity of the installed pipe. Furthermore, more elaborate strength tests or other

geotechnical in-situ or laboratory tests to measure properties of the annular space could be utilized.

Assessment of the annular space in installations made below the water table is suggested for

comparison with the results presented in this research.


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ACKNOWLEDGEMENTS

The financial support to conduct this research project from the Vermeer Manufacturing Company

and Baroid IDP is hereby acknowledged. Additionally, the authors would also like to acknowledge

T.C. Backhoe Services Ltd. of Sherwood Park, Alberta for their professionalism and diligence during

the research project.

Documents

Annular Space Report