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Discussion for Affected Factors of the Carrying Capacity of HDD Drilling Fluid

Hong Gao1, Guohui Li2,Xiaocheng Ma3, Liang Feng4 and Gang Liu5

1 Senior Engineer, Crossing Department, China Petroleum Pipeline Engineering

Cooperation, No.146, Heping Road, Lanfang, Hebei 065000,

Tel:03162074414;Fax:03162073756;Email:cppegaohong@cnpc.com.cn

2 Senior EngineerDirector of Crossing Department, China Petroleum Pipeline

Engineering Cooperation, No.146, Heping Road, Lanfang, Hebei 065000,

Tel:03162074314 Fax:03162073756 Email:cppe_ligh@cnpc.com.cn

3 Engineer Crossing Department, China Petroleum Pipeline Engineering

Cooperation, No.146, Heping Road, Lanfang, Hebei 065000, Tel:03162075754

Fax:03162073756 Email:maxiaocheng@cnpc.com.cn4 MasterCrossing Department, China Petroleum Pipeline Engineering Cooperation,

No.146, Heping Road, Lanfang, Hebei 065000, Tel:03162072354

Fax:03162073756 Email: feng-liang@cnpc.com.cn

5 Senior EngineerCrossing Department, China Petroleum Pipeline Engineering

Cooperation, No.146, Heping Road, Lanfang, Hebei 065000, Tel:03162075489

Fax:03162073756Email:cppeliugang@cnpc.com.cn

ABSTRACT

Although the carrying capacity of the drilling fluid is an important factor for HDD

crossing, it is not only a matter of drilling fluid, some other factors are also related to

it, such as the drillability of the stratum, types of the bit and the reamer, passes of the

hole, mud pressure, velocity of the flow in annular space of the hole, the viscosity

and gravity of the mud, the size and gravity of the cuttings, etc. Till now, it has not

been mentioned yet, and this paper is trying to explore the relationship among these

factors, and expect to make more successful HDD crossings.

KEYWORDS

Horizontal Directional Drilling; Drilling Fluid; Slurry; Drilling Speed; Carrying

Cuttings Rate; Match.

INTRODUCTIONS

Although our country had introduced HDD crossing technology for nearly 30 years,

but the understanding of this technology is far from enough, the specification of

HDD is also not perfect. For example, almost everyone understands that the drilling

fluid(clean mud without cuttings) is a critical matter for the HDD crossing, it

mailto:gaohong@cnpc.com.cnmailto:gaohong@cnpc.com.cn

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should have a good capability of carrying cuttings to clean the hole, which is critical

for the success of HDD crossing. But how to clean the hole is not very clear, and it is

difficulty to find an answer in the relative materials from home and abroad.

Therefore both design and construction are lack of complete and rational guidance. It

seems to be a simple question for the matching between drilling speed and drilling

fluid carrying capacity, but it is a significant issue for cleaning the hole. It also

involves reasonable selection of reaming passes, cuttings carrying rate, velocity of

the flow in annular space of the hole and capacity of mud pump, etc. Diameters of

drill bit and reamers and drilling speed, property of drilling fluid, velocity of the flow

in annular space of the hole (or mud discharge value), cuttings carrying rate

determine the deslagging ability. This article is mainly focus to discuss these

questions, in order to determine a reasonable reaming passes and cuttings carrying

rate, improve the reliability of HDD crossing, so that to complete the crossing with areasonable price.

The drill cutting amount per unit time is equal to the cuttings carrying amount of

drilling fluid per unit time during the HDD crossing construction is the basic point of

this study.

DECITION THE AMOUNT OF CUTTINGS

The amount of cuttings is related with pipeline diameter, reaming passes and drilling

speed.

Factors for reaming passes. The amount of drill cuttings is related to the sizes of bit

and the each reaming , and the reaming size is associated with the life of reamer.

According to the manual of roller bit from Lilin Drill Bit, the reaming size = basic

height of body size + basic height of drill tooth 2, the basic height of tooth is

generally 4 ', 5', 6 ', 7', 8 'and 9 'separately. Recommended cutting height for each

level of reaming is not less than 50% of tooth height, so that, the bearing of the

reamer is sustaining even force, hence it extends the bearing life and prevents early

failure of the drill body, improves the safety of use(Lilin Machinery Group Co. Ltd).For soft stratum, the diameter of each reaming can be larger to save the budget, and

can be achieved by selecting the reaming tool with higher tooth. Contrary for hard

stratum. The reaming size and passes number can be determined according to this

principle.

For example, reaming a hole from 30' diameter(782mm) to 38'914mm,it is suitable

to reaming 3' on each side of the hole, thus a reference height of the drill teeth

equal to or less than 6'(Lilin Machinery Group Co. Ltd).

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Drilling speed.Drill cutting value is related with drilling speed. The drilling speed

can be estimated from rock drillability or empirical parameters.

Dr il lability of rock. The drillability of rock is the key indicator for evaluating the

difficulty of drilling, it is generally use the number of footage in unit time to

represent the level of drillability. The drillability is related with drilling method, drill

bit structure and parameters of drilling process. According to the drillability of core

drilling, the drillability can be divided into 12 classifications which are shown in the

Table 1 as below(Download from Internet).

Table 1. Drillability of Core Drilling Method

Geotechnical

classification

1~3 4~6 7~9 10~12

Geotechnical

title

Soft rock Mid and hard

rock

hard rock Stiff rock

Drillability

m/h

7~2.45 1.6~0.82 0.57~0.25 0.15~0.045

Representative

geotechnical

Loose sand,

containing

10% to 20%

gravel, clay

and sand

gravel,

weatheredshale

Shale, gravel,

crushed stone

and gravel,

calcareous

conglomerate

Phyllite,

gneiss,

coarse-grained

granite,

limestone

breeze

Fine-grained

granite,

quartzite,

chert

I nstallation of Pipeline by Horizontal Dir ectional Dr il li ng an Engineer ing

Design Guide . According to PRCIInstallation of Pipeline by HorizontalDirectional Drilling an Engineering Design Guide, the speeds of pilot hole and

reaming passes are shown in Table 2.2-2 and Table 2.2-3(J.D.Hair &Association,

PRCI, 2008).

Table 2. Product rate of Pilot Hole

ProjectCrossing

Length

Silt, Sand,

Clay

Cobble and

Gravel

Soft rock Hard rock

Productio

n Rate of

Less

Than 30

"(762mm

)

Diameter

Pipe Pilot

ft/h m/h ft/h m/h ft/h m/h ft/h m/h ft/h m/h

2000

609.6 60 18.28

8

45 13.71

6

30 9.14

4

15 4.572

2000

3000

609.6

914.4

55 16.76

4

40 12.19

2

25 7.62 103.04

8

3000

914.4 50 15.24 35 10.66

8

20 6.09

6

Proble

m

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Hole

Productio

n Rate of

Greaterof 30

"(762mm

)

Diameter

Pipe Pilot

Hole

2000

609.6 50 15.24 40 12.19

2

257.62

10 3.04

8

2000

3000

609.6

914.4

45 13.716

35 10.66

8

20 6.09

6

Problem

3000

914.4 40 12.19

2

30 9.144 15 4.57

2

Proble

m

Note: Drilling pipe changing time included.

Table 3. Product rate of Reaming

Diameter Silt, Sand,Clay Cobble andGravel

Soft rock Hard rock

in mm ft/h m/h ft/h m/h ft/h m/h ft/h m/h

24

609.6 180 54.864 129 39.319 60 18.28

8

30 9.144

24

32

609.6

914.4

150 45.72 90 27.432 30 9.144 Proble

m

32

914.4 120 36.576 Proble

m

18 5.486 Proble

m

Note: Drilling pipe changing time included

Horizontal Directional Drilling Trainning Mannual . According to theHorizontal Directional Drilling Training Manual, assuming the drilling fluid is

appropriate quality and the best cuttings carrying rate by drilling fluid is 20%, use

this value to decide reaming speed. After determining the carrying amount and pump

capacity, the drilling speed will be calculated by formula (1)(Houston,Taxas, USA &

Paris France for Sumitomo Metal Industries, Ltd.,1999).

R=W(VQn) (1)where, RMaximum drilling speed, m/min

WOptimal weight carrying amount of ,cuttings, %

VHole volume per meter, m3/m

QnEffective flow of mud pumpm3/min

Practical experience. There is another method to estimate the drilling rate, use the

drilling speed from other project nearby the crossing site, practical experience from

previous project which crossing different stratum, and test drilling or finished drilling

segment drilling speed to estimate. Based on the experience of Longjiang River HDD

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crossing, in the completely weathered and strongly weathered granite stratum, when

use 54 "rock reamer repair and clean the hole, the average time for a single drill pipe

progress is 10 minutes for most segments, which means 57.6m/h, and in some

individual segments, it is estimated that some hard rock dyke is encountered as the

longest time is 218 minutes for a single drill pipe, the equivalent of 2.64m/h. In Liyu

River crossing of another natural gas transmission line, in the medium-slight

weathered limestone (natural compression strength range is 54.4 to 106.0MPa), the

drilling time for some of the single drill pipe is at a maximum 5~6 hours, the

equivalent of 1.92~1.6m/h.

In summary, from the Table 1 of drillability of rock, it can be seen that the drilling

speed is lower than Table 2 and Table 3. As the drillability in Table 1 is related with

the technology used in the drilling, and is used for geological survey, it should betaken as reference only. Table 2 and Table 3 are suitable for HDD crossing processes,

but it should be noted that Table 2 and Table 3 are representing the production rate,

which include the times of changing the drill pipe and each pass reaming , and it is a

composite value related with pipeline diameter, suitable for estimate the construction

period for a project, only be used as a reference for drilling speed. As the drilling

speed in "Horizontal Directional Drilling Training Manual" is derived based on the

condition that suitable drilling fluid property and cuttings carrying rate and given

capability of mud pump, the speed is not suit for design. In the experiences of

Longjiang river and Liyu river crossing, the drilling speed are higher than the speed

in Table 1, but lower than that in Table 2 and Table 3, therefore, the actual

experience is the most accurate and best, and should be collected and accumulated to

form a statistical curve for each crossing company, so as to used as a reference for

design and construction.

DETERMINATION OF CUTTINGS CARRYING AMOUNT

Cuttings carrying amount is related with drilling fluid property, velocity of the flow

in annular space of the hole, optimized cuttings carrying rate, capacity of mud

pump,etc..

Property of drilling fluid. The density, viscosity, colloid rate and static shear

strength of the drilling fluid are closed related with cuttings carrying capacity. The

cuttings carrying amount will be high if these four properties indicators are high

which means the suspension ability of the cutting is high. But higher properties

indicators have some drawbacks, therefore these indicators should be appropriate.

Dr il li ng fl uid density. According to HORIZONTAL DIRECTIONAL DRILLING

GOOD PRACTICE GUIDELINES, typical clean bentonitepolymer drilling fluid

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density is 8.5lb/gal (1.02t/m3), or 3% of the weight of the solid content. The density

of acceptance criteria of slurry (mud containing cuttings) for small and medium-sized

rig is equal or less than 9lb/gal (1.1t/m3) , and for big rig, equal or less than 10lb/gal

(1.2t/m3). U.S. expert suggest that the density of slurry is less than 9lb/gal for

good(HDD consortium, 2001).

In accordance with department specification of Gazprom HDD Underwater

Crossing Construction, the viscosity, colloid rate and static shear strength can be

calculate as follows(,,1998):

Plastic viscosity.

= Q

dl

t

222 )

29.0

.. 2

where-Plastic viscosity, mPa.s

- The cuttings size, m;

Density of cuttings and drilling fluid respectively, kg/m3;

Diameter of the drilling hole, m;

dtDrilling pipe diameter, m;

lThe length of horizontal directional drilling, m;

QAmount of Drilling fluid for mud pump, m3/s;

0.29- Size factor.

Colloidal volume content.

C= ln.b/p 3

whereCVolume content of the clay colloid component, %;

ln-- Natural logarithm of plastic viscosity;

bpDensity of water and drilling fluid respectively, kg/m3

Range of shear stress.

Dynamic shear:T0=23dPs.s 4Static shear: T=T0/3dPs.s 5

Velocity of the Flow in Annular Space of the Hole. Velocity of the flow in annular

space of the hole is related with cuttings size. If the cuttings is with large size and

heavy density, its starting flow speed will be high. The flow speed in annular space

of the hole has the following statements.

No-erosion fl ow veloci ty on the riverbed bottom is used as the min imum fl ow rate

of the slurr y.

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Table 4. Allowable Non-erosion Flow Velocity of the Riverbed for Non-cohesive

Soils

Soil type Category dmm

Non-erosion velocity of riverbed

)(V m/s

Water depth

0.4mWater depth

1m

Clay

silt and mud,

planting soil

containing fine

sand

0.065~0.05 0.15~0.20 0.20~0.30

SandFine sand 0.05~0.25 0.20~0.35 0.30~0.45

Medium sand 0.25~1.00 0.35~0.50 0.45~0.60

Coarse sand 1.00~2.50 0.50~0.65 0.60~0.75

Gravel

Small gravel 2.50~5.00 0.65~0.80 0.75~0.85

Medium gravel 5.00~10.00 0.80~0.90 0.85~1.05

Large gravel 10.00~15.00 0.90~1.10 1.05~1.20

Cobble

Small Cobble 15~25 1.10~1.25 1.20~1.45

Medium Cobble 25~40 1.25~1.50 1.45~1.85Large Cobble 40~75 1.50~2.00 1.85~2.40

Boulder

Small boulders 75~100 2.00~2.45 2.40~2.80

Medium boulders 100~150 2.45~3.00 2.80~3.35

Large boulders 150~200 3.00~3.50 3.35~3.80

Note: The low flow rate is suitable to small size of soil(Download from Internet).

The flow velocity in the above table is the starting velocity in the case of clear water,in the condition of drilling fluid, the starting velocity shall be smaller than that in the

clear water, because of the larger buoyancies and thrust applied by drilling fluid. So

the starting flow of the slurry should be more easier.

Installation of Pipeline by Horizontal Directional Drilling an Engineering

Design Guide . According to INSTALLATION OF PIPELINE BYHORIZONTAL DIRECTIONAL DRILLING AN ENGINEERING DESIGN

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GUIDE, the slurry flow rates during pilot hole drilling, reaming hole and pulling

back are shown in Table 3.2-2, Table 5(J.D.Hair &Association, PRCI, 2008).

Table 5. Mud Flow rate of Pilot Hole

UnitSilt, Sand, Clay Cobble and

Gravel

Soft Rock Hard

Rock

barrels/min/

m3/min

5/0.7945Jet

drilling10/1.589Mud motor drilling

Table 6. Reaming and Pullback Mud Flows

Diameter Silt, Sand, Clay Cobble and

Gravel

Soft Rock Hard Rock

barrels/

minm3/h

barrels/

min

m3/

h

barrels/

min

m3/

h

barrels/

min

m3/

h

24

609.6 7 1.11

210

1.58

9

7 1.11

27

1.11

2

24

32

609.6

914.4

10 1.58

9

132.06

6

101.58

9

Problem

32

914.4 15 2.38

4

Problem 15 2.38

4

Problem

Table 5 and Table 6 are the slurry flow rate during pilot hole drilling, reaming and

pulling back. Using the combination of the slurry flow amount and the hole diameter

for each pass, the slurry flow velocity for each pass can be calculated.

Simple Calcul ation of the Pipes and Pumps.According to Simple calculationof the pipes and pumps, the velocity of the flow in annular space have economic

velocity. Under the condition of the same flow rate, larger diameter pipe have slower

flow velocity which will save the cost on the power, but the cost of pipeline is high.On the contrary, if the cost for smaller diameter of pipeline is saving, but the

electrical power cost will be high. The pipeline resistance = pipe length pipeline

resistance coefficient (velocity)2, from which, it can be seen, the greater the flow

rate, the greater the friction of the hole, the greater the required pump delivery

pressure(China Building Industry Press,1973). With certain power, the greater pump

pressure will decrease the flow rate, and the smaller flow rate may not meet the

requirement of carrying cuttings, and will also cause some problems such as frac-out,

etc. HDD hole does not have the problem of cost of pipeline, but larger holes may

benefit for reducing the slurry transmission cost. For this reason, with same diameter

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of the final hole, larger diameter passes is preferred based on different geological

condition. General flow rate limitation of water pipelines is shown in Table 7.

Table 7. Generally Limits of Water Pipeline Flow Rate

Applicable Conditions Flow Ratem/sOutdoor Long-Distance

Pipelines

DN500 1~1.5

DN500 0.5~1

Pump Outlet Pipe DN200 2~2.5

DN200 1.5~2

Pump Suction Pipe DN200 1.2~1.5

DN200 1~1.2

Workshop General

Pipeline

1.5~2

Empir ical practice. Flow rate is related with pump capacity, and the larger pumping

capacity is, the larger the flow rate and the larger cuttings carrying capacity are, but

greater pumping capacity cost more, and larger flow rate will have serious erosion on

the filter cake due to the slurry, and affecting the stability of the bore hole wall.

Theoretically, the upper limit of velocity of the flow in annular space of the hole

should be the boundary flow rate of laminar and turbulent of non-Newtonian

(Bingham fluid), i.e. in the upper limit of laminar conditions, shall be distinguished

by Bingham fluid critical Reynolds number. The lower limit of the annular velocity

should be starting velocity. As lack of research on the subject of Bingham startingvelocity of the fluid and Bingham fluid critical Reynolds number at present in HDD

industry, a reasonable flow velocity is difficulty to find. From the general practical

experience of HDD crossing, the annulus slurry flow rate shall be higher than 1m/s.

Considering the empirical flow velocity of 1m/s~2m/s is able to comply with the

above methods, and easy for application, it is recommended to use as annular

velocity.

Determination of the cuttings carrying rate.At present, many people are not very

clear of the cuttings carrying rate and two statement for it exist, one of which is solid

particle volume or its weight percentage (including bentonite and additives and

cutting) in the mud (slurry),,and the other is the percentage content of cuttings

volume or weight. Through research, that should be the percentage by weight of

cuttings. The optimal cuttings carrying rate is as follows.

Horizontal dir ectional dri ll ing trainning mannual . According to HorizontalDirectional Drilling Training Manual, the optimal slurry carrying rate shall be 20%

if the drilling fluid quality is suitable(Houston, Taxas , USA & Paris France for

Sumitomo Metal Industries, Ltd., 1999)..

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Horizontal directional dri ll ing good practice guideli ne . From HorizontalDirectional Drilling Good Practice Guidelines, unit weight of water is 8.34lb/gal

(1.02t/m3), unit weight of clean mud (drilling fluid) is 8.5lb/gal (1.02t/m3), unit

weight which is larger than these all comes from solid residue of stratum, and the

carrying weight can be calculate by the Equation 3.3-1(HDD consortium, 2001).

W=m-8.348 6

where:Wweight percent cuttings carrying rate%

munit weight of drilling fluidlb/gal

In addition, for a medium or small rig, the unacceptable weight percentage of slurry

is about 5.3%, and 13.3% is for big rig. For the acceptable criteria of the density of

slurry, the medium and small rigs are equal or less than 9lb/gal1.1t/m3

, which isequivalent to the solid content of 10%, with 7.8% of cutting containing;in it. The big

rig is less or equal to 10lb/gal1.2t/m3, which is equivalent to the solid content of

20% with 17.6% of cutiing containing in it. An U.S. mud expert suggests that the

circulating mud density is best to less than 9lb/gal, which is equivalent to cutting

containing of 7.8%.

Domestic and international oi l and gas pipeli ne HDD crossing engineer ing data

compilation . According to Domestic and international oil and gas pipeline HDDcrossing engineering data compilation, the recommended maximum solid particle

content percentage in the mud is calculated as Equation 3.3-1(Gao K.J. & Dai J.Q.,

1999).

fS=2.917m-14.17 7

where:fSRecommended maximum solid particle content percentage

mUnit weight of drilling fluid, lb/gal

Therefore if m=8.5lb/gal, then fS=10.6%; if m=9lb/gal, then fS=12.1%; if

m=10lb/gal, then fS=15%.

Empir ical cuttings carrying rate. The stratum of Shan-Yin Line Yellow Rivercrossing inclusions round gravel lens dense sand layer, the cuttings carrying rate of

slurry is considered as 10%; The stratum of Guang- Nan trunk branch Longjiang

River HDD crossing is completely weathered and strongly weathered granite,

adopting 5% of cuttings carrying rate.

In summary, the solid content in the slurry is within 5%~20%, HORIZONTAL

DIRECTIONAL DRILLING GOOD PRACTICE GUIDELINES has a clear

formula for calculate the cuttings content, which has complete parameters and clear

meaning, and is easy to use, so it is recommended.

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Determination of mud pump. If annular velocity and bore hole size are given, the

mud pump flow can be calculate by the equation (8).

Qn=SV60 8

where:QnEffective flow of mud pump, m3/min

SBore hole section aream2

VSlurry flow velocitym/s

CONCLUSION

From above results we can see that, to match the speed of drilling and the amount ofthe carried cuttings, the following steps should be considered in the designing.

Determine the maximum diameter of bore hole according to pipeline diameter,and determine reaming passes based on the geological condition and reamer size.

Based on the experience or reference rock drillability and productivity of HDD,or based on the optimal cuttings carrying rate and pump capacity, to determine

the drilling speed.

Determine drilling fluid performance. Unit weights of 1.02 for clean mud and1.1 for containing cuttings mud can be used. And the equations (1)~(5) in this

article can be used to calculate plastic viscosity of the drilling fluid, colloidal

rate and dynamic shear strength and static shear strength..

Determine upper limit flow velocity of laminar flow based on Reynolds numberof Bingham fluid, as a maximum velocity of the flow in annular space of the

hole, or based on the experience to take 1m/s2m/s flow velocity, and the

smaller value and the greater ones is adapted for easily collapse soft stratum and,

hard stratum respectively.

cuttings carrying rates range from 5% to 10% is appropriate, and adopt greatervalue for soft stratum, and smaller value for hard stratum.

Calculate mud pump capacity based on velocity of the flow in annular space ofthe hole and bore hole diameter and pump efficiency. When an optimal cuttings carrying rate and pump capacity are given, the

maximum drilling speed can be calculate based on equation (1).

REFERENCES

Lilin Machinery Group Co.Ltd , Products Introduction

Download from Internet,The Drillability of Core Drilling

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J.D.Hair &Association, PRCI, (2008) Installation of Pipeline by Horizontal

Directional Drilling An Engineering Design Guide

Horizontal Drilling International Houston,Taxas, USA & Paris France for Sumitomo

Metal Industries, Ltd.,(1999) Horizontal Directional Drilling Training Manual

, , Department Specification of Gazprom,(1998) HDD

Underwater Crossing Construction

Download from Internet, Allowable Non-erosion Flow Velocity of the Riverbed for

Non-cohesive Soils

China Building Industry Press , (1973) Simple calculation of the pipes and pumps

HDD consortium (2001), Horizontal Directional Drilling Good Practice Guidelines

Gao K.J. & Dai J.Q.,(1999) Petroleum Industry Press, Domestic and International Oil

and Gas Pipeline HDD Crossing Engineering Data Compilation