Lyons W.C. (ed.). Standard handbook of petroleum and natural gas engineering.2001- Volume 1

Drill String: Composition and Design

725

N.C.

70

7%

REG.'

6%

F.H.

5%

1.F.

7

H-90*

N.C. 61

6%

H-90

6% REG.

5%

F.H.

N.C. 56

REG.

I

N.C.50

Reference Line

Figure

4-130a.

Practical chart

for

drill collar selection-2 +-in.

ID.

(From

Drilco, Division

of

Smith International, Inc.)

726

Drilling and Well Completions

21h"

ID

Reference Line

Figure

4-130b.

Practical chart for drill collar selection-2 +-in.

ID.

(From

Drilco, Division

of

Smith International, Inc.)

Drill String: Composition and Design

727

Reference Line

Figure

4-131a.

Practical chart for drill collar selection-2 +$-in.

ID.

(From

Drilco, Division

of

Smith International, Inc.)

728

Drilling and

Well

Completions

2%

I'

ID

8

7Y4

7%

7'/4

7

6Y4

6Y2

6V4

N.C.

61

6%

H-90

6%

REG.

5Y2

F.H.

N.C.

56

5%

REG.

N.C.

50

N.C.

46

N.C.

44

Y

Reference Line

Figure

4-131

b.

Practical chart for drill collar selection-2 %-in.

ID.

(From

Drilco, Division

of

Smith International, Inc.)

Drill String: Composition

and

Design

729

3”

ID

Reference Line

Figure

4-132a.

Practical chart

for

drill collar selection-3-in.

ID.

(From Drilco,

Division

of

Smith International, Inc.)

730

Drilling and Well Completions

3”

ID

I

N.C*44

Reference Line

Figure

4-1

32b.

Practical chart

for

drill collar selection-3-in.

ID.

(from Drilco,

Division

of

Smith International, lnc.)

Drill String: Composition and Design

731

(text

continued

from

page

722)

Example

Suppose you want to select the best connections for

9

4

x

2

2-in.

ID

drill collars.

For average conditions, you should select in this order of preference (see

Figure

4-131):

1.

Best

=

N.C.

70

(shaded area and nearest reference line.)

2.

Second best

=

7Q

in. REG. (low torque). (Light area to left and nearest to

3.

Third best

=

79

in.

H-90.

(Light area to right and nearest to reference line.)

But in extremely abrasive and/or corrosive conditions, you might want to select

in this order of preference:

reference line.)

1.

Best

=

79

in. REG. (Low torque)

=

strongest box.*

2.

Second best

=

N.C.

70

=

second strongest box.

3.

Third best

=

79

in.

H-90

=

weakest box.

Recommended Makeup Torque for Drill Collars

The rotary shoulder connections must be made up with such torque that the

shoulders will not separate under downhole conditions. This is of critical

importance because the shoulder is the only area of seal in a rorary shoulder

connection. Threads are designed to provide a clearance between crest and root

that acts as a channel for lubricant and also accommodates the small solid particles.

To keep the shoulders together, the shoulder load must be high enough to

create a compressive stress at the shoulder face capable of offsetting the bending

that occurs due to drill collar buckling. This backup load is generated by a

makeup torque. Field observations indicate that an average stress of

62,500

psi

in pin or box, whichever is weaker (cross-sectional area), should be created by

the makeup torque to prevent shoulder separation in most drilling conditions.

It should be pointed out that the makeup torque creates the tensile stress in

the pin and, consequently, the number of cycles for fatigue failure of the pin

is decreased. Therefore, too high a makeup torque has a detrimental effect on

the drill collar service life.

The recommended makeup torque for drill collars is given in Tables

4-75

and

4-76.

Drill Collars Buckling

In a vertical straight hole with no weight on the bit, a string of drill collars

remains straight.

As

the weight for which the straight form of the string is not

stable is reached, the drill string buckles and contacts the wall.

If

weight

on

the bit is further increased, the string buckles a second time and contacts the

borehole wall at two points. With still further increased weight on the bit, the

third and higher order of buckling occurs. The problem

of

drill collars buckling

(text continued

on

page

7?4)

*The connection furthest

to

the left

on

the chart has the strongest box. This connection should he

considered as possible first choice

for

very abrasive formations

or

corrosive conditions.

732

Drilling and Well Completions

Table

4-75

Recommended Makeup Torque

[38]

RECOMMENDED

MAKEUP

TORQUE

(ft-lb)

1%

Note

21

ZSOM

2Wt

ZSlOt

401

1%

3-

3lWt

2MO

Swot

3*0f

am

SI

49001

4200

106

Jv.

5200-

-4200

29W

APlllC

35

VI

N.C.

44

41001

1300t

10000

-

4%

5v.

5%

4li

5%

NOTE:

1

The

calculations tor recommended makeup

toque

assume

the

use

01

a

lhread

compound

containng

40%

10

60%

by weight

of

finely

powdered

metaIIIc

zm,

or

60%

by welghlol

!neb

powdered melallffi

lead,

applied thomughly

to

all threads and shoulders,

the

use

01

the modified jackscrew formula as

shown in the

IADC

Drilling

Manual and the

API

Spec

RP

7G (latest addtlnn). and a unit stress

of

62,500

psi

in the box or

pn.

whichever

IS

weaker

2

Normal toque range

-

tabulated mlnunum value

to

10%

greater Largest diameter shown for e8Ch

conneclion

is

the maxmum recommended for that connection

I1

the

conneclnns are used on dnll

collars larger than the maximum shown.

imrease

tha

toque

values shown

by

10%

lor

a mnimurn value

Drill String: Composition and Design

733

Table

4-76

Recommended Makeup Torque

[38]

RECOMMENDED

MAKEUP TORQUE

(fl-lb)

1%

Note

21

+.-"

32500

1%

40500

7%

49MO

1%

51000

7%

40000

7%

46500

7s

51000

I

>rm

7,h

46000

7%

55000

I

51000

In

SIOO!

ly,

46wv

1%

55MO

I

59500

I

54wo

8%

MUUP

I%

nom

-

I

..-

Y.--

5920

a+

izow

9

7zmg.

I

56000

8%

66000

I'h

74000

I+

14ow

9

14000

9%

14000

In

I+

9%

9

9*

Oy,

9%

10

10%

10

10%

1O'h

10%

11

_______

325mt 405wt

41000

11ooo

4OMOt

48000

moo

(MOO

46WOt

53wo

53000

)Jaw

46WOt

SMOOt

56000

YOOOt

WOOOt

6Mm

68000

38000-

YOOOt

(6000t

10000

7moo

10000

67000t

780001

83000

13000

umo

15000t

8MOOt

101000t

l070W

107000

!0700!-

_~_

-

m

3%

3m0t

M30t

41500

)1y1d

4OOOOt

42000

42000-

46000t

41w0

41000

__

(Iwo

moot

49500

54000t

61000

llmD

%mot

63000

67w0t

1ww

1w00

16000

*

750mt

awwt

lorn00

100000

IOWOO

10~000

IO7WOt

inmot

nmmt

Lmg-

-.

13810

In

addltmn

(0

the

ncmased

mnmum toque value.

It

IS

also recommended that a fishing neck

ba

machined to

the

maximum diameter

shown

3

The

H-90

connectan makeup torque

IS

based

on

56,250

psi stress and other faclors

aa

staled in note

1

4

The

2%''

PAC

makeup torque is

based

on

87,500

psi

stmss

and other

lactors

as

stated

n

note

1

'5

The

iawt diameter

shown

is tha maximum recommended tor

those

lull-face

Wflneclons

If

larger

diameters are used, machine wnnectans with low toque

laces

and

use

the toque values shown under

the

bw

torque

face

lable

If

low

toque

faces am not used,

see

note

2

for

mcreased torque values

t6

Toque

flgures sumeeded

by

a

(t)

indlcate

that

the weaker member

m

torston for

the

corresponding

outside diameter and bore

is

the

BOX

For all other torque values,

the

weaker member

m

torson

is

the

734

Drilling and Well Completions

(texf

continued

from

page

731)

in vertical holes has been studied by

A.

Lubinski [171] and the weight on the

bit that results in first and second order buckling can be calculated as

wcr,

=

1.94(~1p~)‘~ (4-51)

Wcrll

=

3.75( EIp2)‘/’ (4-52)

where

E

=

module of elasticity for drill collars in Ib/ft2 (for steel, E

=

4320

x

lo6

lb/ft2)

p

=

unit weight of drill collar in drilling fluid in lb/ft

I

=

moment of inertia of the drill collar cross-section with respect to its

diameter, in ft

I

=

(~/64)(D:~

-

d4,J

Ddc

=

outside diameter of drill collars in ft

ddc

=

inside diameter of drill collars in ft

Example

Find the magnitude of the weight on bit and corresponding length of drill

collars that result in second order of buckling. Drill collars: 6Q in.

x

2+ ft, mud

density

=

12 lb/gal.

Solution

Moment of inertia:

Unit weight of drill collar in drilling fluid:

p

=

108 1

-

=

88.181b/ft

(

6i24)

For weight on the bit that results in the second order of buckling, use

Equation 4-61:

Wcr,l,

=

3.75(4320

X

lo6

x

4.853

x

Corresponding length of drill collars:

x

88.182)’/3

=

20,468 lb

L,

=--

20’

468

-

232ft

88.18

If the total length of drill collar string would be, for example, 330 ft, then

the number “232 ft” would indicate the distance from the bit to the neutral point.

Lyons W.C. (ed.). Standard handbook of petroleum and natural gas engineering.2001- Volume 1

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