10 Drill String Design

DRILL STRING DESIGN

© 2005 PetroSkills LLC, All Rights Reserved

Drill String Design Common grades of drill pipe with yield strength Grade

E X G S

2

Minimum Yield psi

Maximum Yield psi

Tensile Strength psi

75,000 (517 MPa)

105,000 (724 MPa)

85,000 (586 MPa)

95,000 (655 MPa) 105,000 (724 MPa) 135,000 (931 MPa)

125,000 (862 MPa) 135,000 (931 MPa) 165,000 (1138 MPa)

105,000 (724 MPa) 115,000 (793 MPa) 145,000 (1000 MPa)


Drill String Design

3


Drill String Design The API recognizes four classes of drill pipe New Premium Class Class 2 Class 3

Pipe is rarely considered new If it has been run in the hole, it is considered premium class 4


Drill String Design The DS-1 standard has an additional class of drill pipe It is premium class, reduced TSR The tool joints do not meet the standards for API tool joints and have a reduce torsional strength Pressure and tensile ratings are the same, but torsional strength is lower 5


Drill String Design Premium class assumes that there is 80% wall thickness remaining on the tube and that the reduction in wall thickness comes from the outside diameter of the tube

6


Drill String Design A reduction in outside diameter removes the most steel and results in the lowest strength 5” by 4.276”

5”, 19.5# As = 5.2746 in2 20% outer wall As = 4.1538 in2

20% inner wall As = 4.2855 in2 4.8552” by 4.276” 7

5” by 4.4208” © 2005 PetroSkills LLC, All Rights Reserved

Drill String Design The worn OD can be determined from the following formula





Dpw  Dp  Di  t h  Di The worn OD can be used to calculate tensile strength and combined torsion and tension limits 8


Drill String Design Class 2 has at least 70% of the wall thickness remaining with the loss on the OD Class 2 is seldom used for drilling except small rigs with limited hook load capability Class 3 is less than 70% wall thickness remaining and is considered junk 9


Drill String Design Drill string design starts at the bottom of the hole with the BHA The drill collars must provide enough weight for the bit with the top of the drill collars remaining in tension (not buckled, the top of the drill collars are actually not in axial tension) 10


Drill String Design A design factor (DF) is used to make sure sufficient drill collars are available for estimated weight on bit Typical design factors are 10% to 15% or 1.10 to 1.15 in equation 10-43 W DF  Lc 

11

Wf B


Drill String Design Example shows how to determine the number of drill collars Maximum anticipated weight on 8 3/4 inch (222.3 mm) bit is 50,000 lbs (22,400 daN) Drill collar size is 6 1/2 inch (165.1 mm) by 2 13/16 inch (71.4 mm) Mud weight is 11.5 ppg (1380 kg/m3) Excess collars should be 10% (DF = 1.10) to insure the drill pipe remains in tension

12


Drill String Design The number of 30 foot (9.14 m) collars to be run First determine the weight per foot of the drill collars in air



Wf  2.67 Dp 2  Di 2



 

Wf  2.67 6.52  2.81252  92 lbs per foot Wf  665 k g / m

13


Drill String Design Determine the buoyancy factor B  1 0.015m  B  1  0.01511.5  0.83

Calculate the length of the drill collars W DF  Lc  Wf B

14

500001.10 Lc   720 feet 219.5 m 920.83


Drill String Design Determine the number of collars and weight of collars in drilling fluid 720/30 = 24 drill collars Wtc  24  30  92  0.83  54,979 lbs Wtc  24,643 daN

15


Drill String Design

Neutral Point Drill collars

16


Drill String Design With BHA components, most of the bending will occur in the connections BHA connections are subjected to bending and fatigue from buckling

17


Drill String Design The BSR is a ratio of the relative stiffness of the box and pin for a given connection A typical target BSR is 2.5, +/0.25 Graphs showing the BSR can be found in the API RP 7G

18


Drill String Design 11.5

8.75

11

8.25

7.75

8 5/8 REG

Outside Diameter, inches

Outside Diameter, inches

10.5

8 5/8 H90

10

NC 77

9.5

7 5/8 H90

9

6 5/8 H90 7.25

6 5/8 REG 5 1/2 FH NC56

6.75 5 1/2 H90 5 1/2 REG NC50

6.25

5 H90

NC70

8.5 NC 61 7 H90 3

NC46

6 5/8 FH

2.5

2

5.25 1.5

1

3.5

3

2.5

2

Bending Strength Ratio

Bending Strength Ratio 19

4 1/2 FH NC44 4 H90

NC40

5 1/2 IF

8 3.5

4 1/2 H90

5.75

7 5/8 REG


1.5

1

Drill String Design The BSR for a given connection is a function of the ID of the pin and OD of the box In theory, high BSR’s will cause accelerated pin failures and low BSR’s will cause accelerated box failures

20


Drill String Design The DS-1 standard gives the following recommended BSR’s Drill Collar OD

Traditional API BSR Range

DS-1 Recommended BSR Range

< 6 inches (152 mm)

2.25 to 2.75

1.80 to 2.50

6 to 7 7/8 inches

2.25 to 2.75

2.25 to 2.75

2.25 to 2.75

2.50 to 3.20

(152 - 200 mm) > or = to 8 inches (203 mm) 21


Drill String Design Many operators will place approximately 6 joints of HWDP on top of the drill collars as a transition to the drill pipe It may help reduce drill pipe failures at the top of the drill collars

22


Drill String Design Other operators will rotate the drill pipe from Neutral Point the top of the drill collars on trips 23


HWDP

Drill collars

Drill String Design If jars are placed in a vertical well, they are at the top of the collars and then additional collars (3 to 4) are run above the jars In a vertical well, the jars should not be run in compression

24


Drill String Design Jars are often run in compression in directional wells

HWDP

Drill collars Jars


25


Drill String Design Drill pipe is usually designed with a design factor plus overpull A normal design factor is 1.10 or 10% Overpull can range from 50,000 to 100,000 lbs (22,411 – 44,822 daN) 26


Drill String Design The overpull is the amount that can be pulled on the pipe over and above the drill string weight If the drill pipe consists of more than one weight or grade of pipe, the overpull is balanced between the two strings

27


Drill String Design Example 6 shows how to design the drill string Well depth is 12,000 feet (3658 m) Drill pipe: 5”, 19.50#/ft (127.0 mm, 29.02 kg/m), Grade E, Premium Class and 5”, 19.50#/ft (127.0 mm, 29.02 kg/m), Grade G, Premium Class Design factor is 1.10 Over pull is 100,000 pounds (44,822 daN) 28


Drill String Design Calculate the worn OD of the drill string Dpw  Dp  Di   t h  Di Dpw  5  4.276  0.80  4.276  4.855 " (123.32 mm)

Calculate the cross sectional area of the drill pipe As  As  29

 D 4



pw

2

 Di

 4.855 4



2

2





 4.2762  4.152 in2 (2679 mm2 ) © 2005 PetroSkills LLC, All Rights Reserved

Drill String Design Calculate the tensile strength of the grade E pipe Tst  Yp  As

Tst  75,000  4.152  311,000 pounds 141,067 kg

Calculate the tensile strength of the grade G pipe Tst  105,000  4.152  436,000 pounds 197,767 kg

30


Drill String Design

31


Drill String Design The maximum pull on the grade E with the 1.10 design factor would be:

32

Pmax

Tst  DF

Pmax

311000   283,000 pounds (128,367 kg) 1.10


Drill String Design The maximum weight of grade E that can be used with 100,000 pounds over pull is: Wmax  283000  54979  100000  128,021lbs 58,069 kg

The maximum length of grade E drill pipe that can be used is: Lmax 

33

128021  6565 feet (2001m) 19.50


Drill String Design The maximum pull on the grade G with the 1.10 design factor would be: Pmax

34

436000   396,000 pounds 179,623 kg 1.10


Drill String Design The maximum weight of grade G that can be used with 100,000 pounds over pull is: Wmax  396000  54979  100000  128021  113,021 pounds Wmax  51,266 kg

35


Drill String Design The maximum length of grade G drill pipe that can be used is: Lmax 

36

113000  5795 feet 1766 m 19.50


Drill String Design The drill string would consist of the following: 720 feet of drill collars (219.5 m) 6565 feet (2001 m) of 5”, 19.50#/ft, (127.0 mm, 29.02 kg/m) grade E drill pipe and 4715 feet (1437 m) of 5”, 19.50#/ft, (127.0 mm, 29.02 kg/m) grade G drill pipe 37


Drill String Design

Top of Grade E Drill Pipe

HWDP


38


Drill String Design Class Problem – Design the drill string Drill 12 ¼” (311.2 mm) hole to 10,000’ (3048 m) Maximum bit weight is 65,000 lbs (29,000 daN) Collars 8” OD (203.2 mm) by 2 13/16” ID (71.4 mm) 4 ½”, 16.60 (114.3 mm, 24.7 kg/m) Grade E, Premium 4 ½”, 16.60 (114.3 mm, 24.7 kg/m) Grade S135, Premium Use 1.10 design factor for collars Design factor of 1.10 with overpull of 75,000 lbs (34,000 daN) for drill pipe Mud weight is 9.5 ppg (1140 kg/m3) 39


Drill String Design The drill string would consist of the following: 570 feet (173.7 m) of drill collars (19) 5300 feet (1615 m) of 4 1/2”, 16.60#/ft (114.3 mm, 24.7 kg/m), grade E drill pipe and 4130 feet (1259 m) of 4 1/2”, 16.60#/ft (114.3 mm, 24.7 kg/m), grade S drill pipe 40


Drill String Design First determine the weight per foot of the drill collars in air



Wf  2.67 Dp 2  Di 2



 

Wf  2.67 8 2  2.8125 2  150 lbs/ft (223 kg/m)

41


Drill String Design Determine the buoyancy factor B  1 0.015m 

B  1  0.0159.5  0.86

Calculate the length of the drill collars W DF  Lc  Wf B

42

650001.10 Lc   554 feet (168.9 m) 1500.86


Drill String Design Determine the number of collars and weight of collars in drilling fluid 554/30 = 18.5 drill collars Use 19 drill collars Wtc  19  30  150  0.86  73,530 lbs 33,353 kg

Get the tensile strength of pipe from the API spec 43


Drill String Design

44


Drill String Design The maximum pull on the grade E with the 1.10 design factor would be: Pmax

Tst  DF

Pmax 

45

260,165  236,513 pounds (107,281kg) 1.10


Drill String Design The maximum weight of grade E that can be used with 75,000 pounds over pull is: Wmax  236,513  73,530  75,000  87,983 pounds Wmax  39,908 kg

The maximum length of grade E drill pipe that can be used is: Lmax  46

87,983  5300 feet 1515 m 16.60 © 2005 PetroSkills LLC, All Rights Reserved

Drill String Design The maximum pull on the grade S with the 1.10 design factor would be: 468,297  425,725 pounds 1.10  193,106 kg

Pmax  Pmax

47


Drill String Design The maximum weight of grade S that can be used with 75,000 pounds (34,019 kg) over pull is: Wmax  425,725  73,530  75,000  87,983  189,212 pounds Wmax  85,825 kg

48


Drill String Design The maximum length of grade S drill pipe that can be used is: Lmax 

49

189,212  11,398 feet 3474 m 16.50


Drill String Design The drill string would consist of the following: 570 feet (173.7 m) of drill collars (19) 5300 feet (1615 m) of 4 1/2”, 16.60#/ft (114.3 mm, 24.7 kg/m), grade E drill pipe and 4130 feet (1259 m) of 4 1/2”, 16.60#/ft (114.3 mm, 24.7 kg/m), grade S drill pipe 50


Drill String Design In directional wells, the pipe weight available for bit weight is a function of the inclination Bit Weight = W cos I

Inclination, I W

Normal Force = W sin I 51


Drill String Design Most of the drill collars are often replaced by heviwate drill pipe (HWDP). Helps reduce torque and drag by reducing string weight Fewer drill collar connection failures 52


Drill String Design The body of a drill collar is stiffer than the connection and bending occurs in the connection In HWDP, bending occurs in the body and not at the connection, so fewer connection failures are experienced

53


Drill String Design Frequently, the drill pipe is also run in compression for bit weight In a vertical well, drill pipe will buckle with little or no compressive load Buckling will create bending stresses in the drill pipe which can lead to fatigue if the bending stresses are high enough In a directional well, the compressive load must exceed the critical buckling load in order to buckle the drill pipe 54


Drill String Design Therefore, drill pipe can be run in compression in a directional well without causing buckling provided the compressive load is less than the critical buckling load Fcrit Fcrit

EIAg sin I 2 r

Basic Units

9.82  105 (OD 4  ID 4 )(Wt / ft) B sin I  ( Dh  OD)

 English Units 55


Drill String Design The critical buckling load is a function of the pipe size, inclination and radial clearance

56


Drill String Design 40,000

Critical Buckling Load, lbf

35,000 30,000 25,000 20,000 15,000 10,000

4 1/2" in 8 1/2" Hole 4 1/2" in 12 1/4" Hole 5" in 8 1/2" Hole

5,000

5" in 12 1/4" Hole

0

10

20

30

40

50

Inclination 57


60

70

80

90

Drill String Design Buckling is actually a little more complicated It also depends upon the curvature of the wellbore, internal pressure and external pressure The DS-1 Standard has more detailed buckling calculations

58


Drill String Design The pipe weight and grade can be identified by the pin end, tool joint

59


Drill String Design Pipe weight codes can be found in Table 17 Grade Grade Code E-75 E X-95 G-105 S-135 60

X G S © 2005 PetroSkills LLC, All Rights Reserved

Drill String Design Pipe Weight Code

Pipe Grade Code

Standard Weight Grade E Drill Pipe

Heavy Weight Grade E Drill Pipe

Pipe Weight Code

Pipe Weight Code

Pipe Grade Code

Pipe Grade Code

Standard Weight High Strength Drill Pipe

Heavy Weight High Strength Drill Pipe

Old API markings for tool joints 61


Drill String Design

Standard Weight Grade E-75 Drill Pipe

Standard Weight Grade G-105 Drill Pipe

Standard Weight Grade X-95 Drill Pipe

Standard Weight Grade S-135 Drill Pipe

Mill slot and groove method of drill string identification 62


Drill String Design Drill pipe identification is not strictly followed and you have to look Pipe Weight Code

Pipe Grade Code

Heavy Weight Grade E-75 Drill Pipe

Heavy Weight Grade X-95 Drill Pipe

Heavy Weight Grade G-105 Drill Pipe

Heavy Weight Grade S-135 Drill Pipe

Mill slot and groove method of drill string identification 63


Drill String Design Combined torque and tension When torque is added to the drill pipe, the tensile strength is reduced At low values of torque, the tensile strength does not change substantially As torque increases, the tensile strength decreases

64


Drill String Design The equation for calculating the maximum allowable torque based on tension is as follows:  0.096167 J  2 T  Yp  QT   2   D pw As    2

0.5

English

 1.1536  10 J  2 (9800T ) Y p  QT   2   D As pw   6

65


2

0.5

 SI  

Drill String Design 60,000

Torque, ft-lbs

50,000

40,000

30,000

19,242 ft-lbs (26,119 N-m) 20,000

250,000 lbs (112,000 daN) 10,000

0 0

100,000

200,000

300,000

400,000

500,000

Tension, pounds Grade E

66

Grade X

Grade G


Grade S

600,000

Drill String Design Drill string inspection Periodically the drill string must be inspected to make sure that the pipe and BHA components are still fit for purpose There are no API standards for drill string inspection; however, some of the industry uses the inspection standards in the DS-1 67


Drill String Design Service Category 1 Very shallow, very routine wells in well-developed areas When drill stem failures occur, failure costs are so minimal that the cost of extensive inspection would not have been justified

68


Drill String Design Service Category 2 Routine drilling conditions where the established practice is to perform minimal inspection and failure experience is low

69


Drill String Design Service Category 3 Mid-range drilling conditions where a standard inspection program is justified If a failure occurs, the risk of significant fishing cost or losing part of the hole is minimal

70


Drill String Design Service Category 4 Drilling conditions more difficult than Category 3 Significant fishing cost or losing part of the hole is likely in the event of a drill stem failure

71


Drill String Design Service Category 5 Severe drilling conditions Several factors combine to make the cost of a possible failure very high

The service category is selected by the operator depending upon their risk analysis

72


Drill String Design Directional wells will have a higher service category than vertical wells Very deep, very high pressure and sour wells are beyond the scope of the DS-1 Standard

73


Drill String Design

74


Drill String Design The BHA components should be inspected before they are picked up After the components have been picked up, additional inspections should be carried out at regular intervals

75


Drill String Design

76


10 Drill String Design

Recommend Documents