Drill collars are important bottom tools in oil and gas drilling operations, and their standards and specifications are crucial to ensure their performance and safety. Drill collars have thick wall structures and large weight and rigidity. They are mainly used to provide drilling pressure to the drill bit and maintain the wellbore trajectory. Therefore, when manufacturing and using drill collars, industry standards and specifications must be strictly followed to ensure their reliability in complex downhole environments.
1. API standards and specifications
API (American Petroleum Institute) is the most important standard-setting organization in the oil industry. Its standards cover the design, manufacturing, material selection, mechanical properties and other aspects of drill collars. The main API standards for drill collars include:
API Spec 7-1:
API Spec 7-1 specifies the materials, dimensions and manufacturing processes of drill collars, requiring the use of high-strength alloy steel such as AISI 4145H. This material has excellent mechanical properties and is suitable for withstanding high pressure downhole and complex loads during drilling. API Spec 7-1 also puts forward clear requirements for the heat treatment of drill collars to ensure that the drill collars have sufficient strength and toughness.
API Spec 5DP:
This standard mainly regulates the connection between drill collars and
drill pipes and
drill bits, including commonly used thread types (such as NC, REG, FH, IF, etc.) and their specific specifications (such as NC26, NC38, etc.). Threaded connection is a key part of drilling operations and must be safe and reliable under extreme load conditions.
API RP 7G:
API RP 7G recommends the use and maintenance of drill collars, and regulates the operation, maintenance and field use of drill collars to ensure their safety during long-term use.
2. ISO standards
ISO (International Organization for Standardization)** standards are also widely used in the manufacture and testing of drill collars, such as ISO 11961 and ISO 17160. Similar to API standards, they put forward detailed requirements for the mechanical properties and connection specifications of drill tools to ensure the consistency and interchangeability of drill tools produced globally.
ISO 11961: Covers the mechanical performance requirements of drill pipes and drill collars to ensure that drill tools can withstand the complex stresses in extreme underground environments.
ISO 17160: Focuses on the threaded connection of drill collars to ensure that drill tools from different manufacturers can be safely interchanged.
3. NACE and other standards
NACE MR0175/ISO 15156:
This standard specifies the requirements for drill collars to resist hydrogen sulfide corrosion in acidic environments. In particular, for underground operations containing hydrogen sulfide gas, drill collar materials and processing that meet NACE standards must be used.
ASTM and ASME standards:
ASTM and ASME standards further standardize the performance testing of drill collar materials and the technical requirements in the manufacturing process. The ASTM A370 standard is used to test the tensile and hardness properties of drill collar materials, while the ASME standard is widely used in some pressure equipment and welding processes.
4. Main specification requirements for drill collars
Material selection:
Drill collars are usually made of high-strength alloy steel (such as AISI 4145H). This material has both high hardness and good toughness, and can cope with underground high pressure, high temperature, and acidic corrosive environments. In order to ensure material performance, the control of trace elements during the manufacturing process is crucial.
Heat treatment process:
Drill collars are usually quenched and tempered to improve their mechanical properties. API and ISO standards have detailed regulations on the hardness range of drill collars to ensure that they can withstand high external loads without being too brittle.
Threads and connections:
The threaded connection of the drill collar must meet the specifications of API and ISO standards. The processing accuracy of the thread directly affects the connection strength between the drill collar and the drill pipe. Common thread types include NC26, NC38, etc. API 5DP specifies the specific dimensions and load capacity of these threads.
Non-destructive testing:
Drill collars must undergo strict non-destructive testing (such as ultrasonic and magnetic particle testing) before leaving the factory to ensure that there are no defects inside the drill collars and that they can work stably for a long time in the harsh downhole environment.
Size and length:
The outer diameter of the drill collar is usually between 3 1/8 inches and 11 inches, and the length is commonly 30 feet, 31 feet or 43 feet. Drill collars of different lengths can also be customized according to the standards of API R1, R2, and R3 to meet the needs of downhole operations at different depths.
Drill collar Specifications:
Drill Collor Number*
|
Outside Diameter,
in.
|
Inside Diameter,
in.
|
Length,
ft
|
Approximate Weight,
lb/ft
|
Typical Bending
Strength Ratio
|
NC 23-31
|
3-1/8
|
1-1/4
|
30
|
22
|
2.57:1
|
NC 26-35 (2-3/8 IF)
|
3-1/2
|
1-1/2
|
30
|
27
|
2.42:1
|
NC 31-41 (2-7/8 IF)
|
4-1/8
|
2
|
30 or 31
|
34
|
2.43:1
|
NC 35-47
|
4-3 /4
|
2
|
30 or 31
|
47
|
2.58:1
|
NC 38-50 (3-1/2 IF)
|
5
|
2-1/4
|
30 or 31
|
54
|
2.38:1
|
NC 44-60
|
6
|
2-1/4
|
30 or 31
|
83
|
2.49:1
|
NC 44-60
|
6
|
2-13 /16
|
30 or 31
|
76
|
2.84:1
|
NC 44-62
|
6-1/4
|
2-1/4
|
30 or 31
|
91
|
2.91:1
|
NC 46-62 (4 IF)
|
6-1/4
|
2-13 /16
|
30 or 31
|
84
|
2.63:1
|
NC 46-65 (4 IF)
|
6-1/2
|
2-1/4
|
30 or 31
|
100
|
2.76:1
|
NC 46-65 (4 IF)
|
6-1/2
|
2-13 /16
|
30 or 31
|
93
|
3.05:1
|
NC 46-67 (4 IF)
|
6-3 /4
|
2-1/4
|
30 or 31
|
109
|
3.18:1
|
NC 50-70 (4-1/2 IF)
|
7
|
2-1/4
|
30 or 31
|
118
|
2.54:1
|
NC 50-70 (4-1/2 IF)
|
7
|
2-13 /16
|
30 or 31
|
111
|
2.73:1
|
NC 50-72 (4-1/2 IF)
|
7-1/4
|
2-13 /16
|
30 or 31
|
120
|
3.12:1
|
NC 56-77
|
7-3 /4
|
2-13 /16
|
30 or 31
|
140
|
2.70:1
|
NC 56-80
|
8
|
2-13 /16
|
30 or 31
|
151
|
3.02:1
|
6-5/8 API Reg
|
8-1/4
|
2-13 /16
|
30 or 31
|
162
|
2.93:1
|
NC 61-90
|
9
|
2-13 /16
|
30 or 31
|
196
|
3.17:1
|
7-5/8 API Reg
|
9-1/2
|
3
|
30 or 31
|
217
|
2.81:1
|
NC 70-97
|
9-3 /4
|
3
|
30 or 31
|
230
|
2.57:1
|
NC 70-100
|
10
|
3
|
30 or 31
|
243
|
2.81:1
|
8-5/8 API Reg
|
11
|
3
|
30 or 31
|
300
|
2.84:1
|
O.D.
|
cutting depth
|
Lead ±25.4
|
mm
|
in
|
A(mm)
|
B(mm)
|
mm
|
86
|
3.375
|
3.5±0.79
|
/
|
679
|
98.4
|
3.875
|
4.0±0.79
|
/
|
914
|
101.6~111.1
|
4~4 1/8
|
4.8±0.79
|
/
|
914
|
114.3~130.2
|
4 1/2~5 1/8
|
5.6±0.79
|
/
|
965
|
133.4~146.1
|
5 1/4~5 3/4
|
6.4±0.79
|
/
|
1067
|
149.2~161.9
|
5 7/8~6 3/8
|
7.1±1.59
|
/
|
1067
|
165.1~177.8
|
6 1/2~7
|
7.9±1.59
|
/
|
1168
|
181.0~200.0
|
7 1/8~7 7/8
|
8.7±1.59
|
5.6±0.79
|
1626
|
203.2~225.4
|
8~8 7/8
|
9.5±1.59
|
6.4±0.79
|
1727
|
228.6~250.8
|
9~9 7/8
|
10.3±2.37
|
7.1±1.59
|
1829
|
254.0~276.2
|
10~10 7/8
|
11.1±2.37
|
7.9±1.59
|
1930
|
279.4
|
11
|
11.9±2.37
|
8.7±1.59
|
2032
|
5. Conclusion
The standards and specifications of
drill collars are the basis for ensuring their safe and reliable operation in oil and gas drilling operations. International standards such as API, ISO, and NACE have detailed regulations on various aspects of drill collar materials, manufacturing processes, threaded connections, and performance testing to ensure that drill collars can adapt to complex downhole environments. For oil companies and drilling tool manufacturers, strict compliance with these standards and specifications is the core of ensuring the efficiency and safety of drilling operations.