Schlumberger - Drill String Design Manual

Schlumberger Sedco Forex
Engineering Department
Author:
M. Andrea
Reviewed by:
Approved by:
Engineering Recommendations
Ref.:
Page: 1 of 23
Issued:
Revision: 00
Drill String Design Recommendations
Summary
This document provides the principals utilized for drill string design in the oil well drilling industry.
These specifications can be used whenever designing a drill string, with agreement from the
Regional Technical/Operations Managers
This uncontrolled document has been issued using Microsoft WORD 7.0 for Windows 95. Copies are
available from Drilling Engineering in Montrouge.
00 First Issue 20/04/98
Revision
Number Description of amendments / page changes/comments Date dd/mm/yy

ENG-
Revision: 00 DRILL STRING DESIGN Issued: Page: 2 of 23
Table of Contents
1. Purpose .............................................................................................................................................3
2. Scope.................................................................................................................................................3
3. Responsibility....................................................................................................................................3
4. References.........................................................................................................................................3
5. Distribution, filing and storage of this document.............................................................................3
6. Abbreviations and Definitions used..................................................................................................3
6.1. Abbreviations.............................................................................................................................3
6.2. Definitions.................................................................................................................................4
7. Drill Pipe Properties.........................................................................................................................4
7.1 Drill Pipe Grade..........................................................................................................................4
7.2 Drill Pipe Class...........................................................................................................................4
7.3 Tool Joints ..................................................................................................................................4
7.4 Thread Form...............................................................................................................................5
8. Drill Collars......................................................................................................................................5
8.1 Drill Collar Selection..................................................................................................................5
8.2 Size Criteria................................................................................................................................6
8.3 Drill Collar Connections.............................................................................................................7
9. Allowable Weight on Bit ..................................................................................................................8
9.1. Discussion Vertical Holes...........................................................................................................8
9.2. Discussion Inclined Holes ..........................................................................................................9
9.3 Vertical Hole Calculation Procedure..........................................................................................10
9.4 Inclined Hole Calculation Procedure ........................................................................................11
9.5 Weight of BHA Required .........................................................................................................12
10. Tension..........................................................................................................................................12
10.1 Static Load..............................................................................................................................12
10.2 Margin of Over Pull................................................................................................................12
11.Burst...............................................................................................................................................13
11.1 Pipe Burst Calculation.............................................................................................................14
12. Collapse.........................................................................................................................................14
12.1 Drill pipe collapse...................................................................................................................14
12.2 Effect of tensile load on collapse..............................................................................................14
12.3 Slip crushing...........................................................................................................................16
13. Pipe Torsion..................................................................................................................................17
13.1 Torsion Only...........................................................................................................................17
13.2 Torsion and Tension ...............................................................................................................17
14. Fatigue ..........................................................................................................................................18
14.1 Limits .....................................................................................................................................18
14.2 Fraction of Drill Pipe Life Expended in Dogleg.......................................................................19
15. Tool Joint Performance................................................................................................................20
15.1 Make-up and Yield Torque......................................................................................................20
15.2 Combined Torsion and Tension to Yield a Rotary Shouldered connection ...............................21
16. Combination Tube and Connection Performance........................................................................22
17. Critical Rotary Speeds .................................................................................................................23
17.1 Transverse Vibration...............................................................................................................23
17.2 Axial Vibration.......................................................................................................................23
17.3 Harmonic Vibrations...............................................................................................................23

ENG-
Revision: 00 DRILL STRING DESIGN Issued: Page: 3 of 23
1. Purpose
These procedures shall be used whenever designing a drillstring, unless otherwise decided with the
Region Technical/Operations Managers.
2. Scope
The manual gives the theory, guidelines and design factors for proper drillstring design. The following
design factors shall apply when designing a drillstring:
Tension 1.1
Margin of over pull 50,000 to 100,000 lbs
Excess BHA weight 1.15
Torsion 1.0 (based on lesser of pipe body or connection strength)
Collapse 1.1. to 1.15
Burst 1.2
The design process shall address the following items:
1. Selection of drill collar diameter
2. Selection of BHA connections
3. Determination of drill collar and or HWDP length
4. Tool joint torsional capacity check
5. Tension design limitations
6. Burst pressure determination
7. Collapse pressure determination
8. Slip crushing load
9. Fatigue limits
10. Combined tension and torsional load limits
3. Responsibility
The Region Technical/Operations Managers are responsible of the enforcement of this standard
throughout the SF organization
4. References
Engineering Standard RE-ST-516-01 issued November 1992
API specification 5D (SPEC 5D), 3 rd edition, August 1, 1992 or latest edition
API specification 7 (SPEC 7), 38 th edition, April 1994, or latest edition
API Recommended Practice 7G (RP 7G), 15 th edition, January 1, 1995, or latest edition
5.Distribution, filing and storage of this document
In accordance with Procedure RE-PR-M&M-02, this document shall be inserted in:
- MPP manual volume 4, PSS Family Number: 516
6.Abbreviations and Definitions used
6.1. Abbreviations
SF: Sedco Forex
HQS :the Headquarters of SF located in Montrouge France
Eng: the Engineering Department of SF located in Montrouge.
M & M: Materials & Maintenance department within R & E
PSS: Property Symbolization System used within Sedco Forex.
MPP: Maintenance Policies and Procedures
API: American Petroleum Institute

ENG-
Revision: 00 DRILL STRING DESIGN Issued: Page: 4 of 23
6.2.Definitions
Bench mark: reference mark machined on the pin and box areas adjacent to the shoulder.
7. Drill Pipe Properties
7.1 Drill Pipe Grade
Each joint of drill pipe includes the tube body and the tool joint, which connects the sections of drill pipe.
Drill pipe is available in several sizes and weights. The grade of drill pipe describes the minimum yield
strength of the pipe. This value is important because it is used in burst, collapse, and tension
calculations. Common grades are as follows:
Grade
Letter Designation Assumed Average Yield Strength (psi)
(used for collapse)
Minimum Yield Strength
(psi)
D-55 65,000 55,000
E-75 85,000 75,000
X-95 110,000 95,000
G-105 120,000 105,000
S-135 145,000 135,000
7.2 Drill Pipe Class
Drill pipe is unlike most other oil-field tubulars, such as casing and tubing, because it is used in a worn
condition. Casing and tubing are usually new when installed in a well. As a result, “classes” are given
to drill pipe to account for wear. Therefore, drill pipe must be defined according to its nominal weight,
grade, and class. The API has established guidelines for pipe classes in API Recommended Practice
7G. Although the class definitions can be extensive, they are summarized as follows:
New -No wear and has never been used.
Premium - Uniform wear and minimum wall thickness of 80%.
Class 2 - Allows drill pipe with a minimum wall thickness of 65% with all wear on one side so
long as the cross-sectional area is the same as premium class; that is to say, based
on not more than 20% uniform wall reduction.
Class 3 -Allows drill pipe with a minimum wall thickness of 55% with all wear on one side.
7.3 Tool Joints
Tool joints are screw-type connectors that join individual joints of drill pipe. Most tool joints, regardless
of the drill pipe tube grade on which they are installed, are made of 120,000 psi yield strength material.
Several types are widely used:
IEU (internal-external upset) Tool joint is larger than the pipe such that the tool joint ID is less than
the drill pipe. The tool joint OD is larger than the drill pipe. Generally
IEU connections are the strongest available couplings.
IF (internal flush) Tool joints ID is approximately the same as the pipe. The OD is
upset.
IU (internal upset) Tool joint ID is less than the pipe. Tool joint OD is approximately the
same as the pipe. This type is often termed “slim-hole” pipe because
of the reduced outer clearance.
An important note about tool joints is that they are designed to be run in tension.
Hardfacing, of hardbanding, tool joints has become a common practice in the drilling industry. To
minimize tool joint wear while rotating on abrasive rock, a band of abrasion-resistant material is applied
to the outside of the box tool joint. This material is usually sintered tungsten carbide particles in a
welded metal matrix. The problem that often arises from the use of hardfaced tool joints is excessive
wear on the internal diameter on the casing.

ENG-
Revision: 00 DRILL STRING DESIGN Issued: Page: 5 of 23
7.4 Thread Form
The term “rotary shouldered connection” refers to the threads of the pin or box of drill pipe or drill
collars. The threads of the pin of one joint engage with the threads of the box of another joint during
make-up . The actual seal is provided by the metal contact of the shoulders of the tool joints. The
engaged threads are not made to provide a seal and open channels between the threads exist, even
when the joint is torqued.
Besides thread form and number of threads per inch, a connection can also be distinguished by
dimensional data relating to the small and large diameters of pin, box bore, length of pin and box, etc.
API suggests the use of the term “number connection” (NC) to distinguish the various sizes and styles
of rotary connections. The NC refers to the pitch diameter of the pin thread at gauge point when
rounded to units and tenths of inches, Thus if the pitch diameter is 1.063 in, the first two figures are
used, i.e. 10, to provide a description of the connection as NC10.
8. Drill Collars
8.1 Drill Collar Selection
Drill collars are the predominant components of the bottom-hole assembly. Some of the functions of
the drill collars are as follows:
• Provide weight for the bit
• Provide strength needed to run in compression
• Minimize bit stability problems from vibrations, wobbling, and jumping
• Minimize directional control problems by providing stiffness to the BHA
Proper selection of drill collars (and BHA ) can prevent many drilling problems. Drill collars are available
in many sizes and shapes, such as round, square, triangular, and spiral grooved. The most common
types are round (slick) and spiral grooved. Spiral-grooved collars reduce the surface contact area
between the pipe and well bore. The lower contact area reduces the probability of differential pressure
sticking. Table 8.1 (below) shows the API dimensions for collars of various outer diameters.
Drill Collar Number OD, in. Bore +1/16 -0, in.
NC23-31 (tentative) 3 1/8 1 ¼
NC26-35 (2 3/8 IF) 3 ½ 1 ½
NC31-41 (2 7/8 IF) 4 1/8 2
NC35-47 4 ¾ 2
NC38-50 (3 1/2 IF) 52 ¼
NC44-60 62 ¼
NC44-60 62 13/26
NC44-62 6 ¼ 2 ¼
NC46-62 (4IF) 6 ¼ 2 13/26
NC46-65 (4IF) 6 ½ 2 ¼
NC46-65 (4IF) 6 ½ 2 13/16
NC46-67 (4IF) 6 ¾ 2 ¼
NC50-70 (4 ½ IF) 72 ¼
NC50-70 (4 ½ IF) 72 13/16
NC50-72 (4 ½ IF) 7 ¼ 2 13/16
NC56-77 7 ¾ 2 13/16
NC56-80 82 13/16
6 5/8 REG 8 ¼ 2 13/16
NC61-90 92 13/16
7 5/8 REG 9 ½ 3
NC70-97 9 ¾ 3
NC70-100 10 3
NC77-110 (tentative) 11 3