Drill Collar Meaning
A drill collar is a crucial component of the drill string in drilling operations, located at the bottom of the string. It serves as the main part of the lower drilling tool assembly. The primary purpose of the drill collar is to provide weight to the drill bit, ensuring it maintains proper contact with the formation and efficiently penetrates rock layers. Drill collars are characterized by their large wall thickness (typically 38 to 53 mm, which is 4 to 6 times thicker than the wall of drill pipes), high gravity, and rigidity. These features play a significant role in stabilizing the drill string and maintaining the proper weight on the drill bit.
Definition of Drill Collar
A drill collar is a thick-walled steel pipe used in the oil and gas industry. It is part of the drill string and is designed to provide the necessary weight and stability for the drilling process. Unlike drill pipes, which are hollow, drill collars are solid and heavy. Their primary function is to push the drill bit into the formation, ensuring efficient penetration. Due to their high density and rigidity, drill collars are essential for preventing the drill string from bending and for maintaining proper weight distribution.
The Role of Drill Collar in Drilling
Drill collars are critical for providing the necessary weight and stability during the drilling process. Their significant mass helps push the drill bit into the formation, ensuring effective cutting and minimizing bit bouncing. Additionally, drill collars are designed to withstand the harsh conditions encountered during drilling, such as high temperatures, high pressures, and intense wear and tear.
Features of Drill Collars
Large Wall Thickness: Drill collars typically have a wall thickness of 38 to 53 mm, which is significantly thicker than drill pipes. This thick wall adds to their rigidity and strength.
Heavy Weight: The solid construction of drill collars provides substantial weight, ensuring the drill bit remains in proper contact with the formation.
Rigidity: Drill collars offer the necessary stiffness to prevent buckling or bending during deep drilling operations.
Surface Features: To assist with the drilling process, the outer surface of the drill collar may be equipped with grooves, such as hanging card grooves and slip grooves, which help with tool handling and positioning in the hole.
Drill Collar Size Chart
Choosing the correct drill collar size is essential for optimizing drilling efficiency. A typical drill collar size can range in outer diameter from 2.375 inches to 6 inches, with weight per foot varying between 60 lbs and 200 lbs. The right size and weight will depend on the depth and nature of the well being drilled.
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
|
|
Drill collar Mechanical Performance
|
|
OD
|
Yield Strength
|
Tensile Strength σb
|
Elongation
|
Reduction of are
|
Impact
|
|
Size
|
σ0.2
|
Mpa(psi)
|
δ4%
|
%
|
Ft.1b
|
|
|
Mpa(psi)
|
|
|
|
|
|
3 1/8~6 3/4
|
≥758
|
≥827
|
≥18
|
50
|
≥50
|
|
-110,000
|
-120,000
|
|
7~10
|
≥689
|
≥758
|
≥20
|
|
-100,000
|
-110,000
|
Sreel Mark
|
Drill collar Chemical Composition %
|
|
C
|
Si
|
Mn
|
P
|
S
|
Cr
|
Mo
|
Cu
|
Al
|
|
4145H
|
0.42～0.48
|
0.15～0.35
|
0.90～1.20
|
≤0.03
|
≤0.03
|
0.90～1.20
|
0.15～0.25
|
≤0.2
|
0.025～0.045
|
|
Other Elements：N≤0.015，Ni≤0.5
|
Drill Collar Standard: API 5DP/API Spec 7-1
Drill collars are crucial components in drilling operations, and their quality is governed by specific industry standards such as API 5DP and API Spec 7-1.
API 5DP is a standard for drill pipes, including specifications related to the mechanical properties of drill collars. It ensures the materials used in drill collars are strong and resistant to wear and corrosion.
API Spec 7-1 specifically governs drill collars, focusing on material composition, tensile strength, dimensional accuracy, and thread specifications. It ensures drill collars can withstand high pressure and harsh conditions, providing durability and safety during drilling operations.
Both standards help maintain quality, safety, and compatibility, ensuring drill collars are reliable and fit seamlessly within the drill string for efficient performance.
Drill Collar and HWDP
The term
drill collar and HWDP (Heavy Weight Drill Pipe) refers to the combination of drill collars and heavy-weight
drill pipe. While both serve to add weight to the drill string,
HWDP is typically lighter than drill collars but still plays an important role in stabilizing the drilling assembly. The drill collar and HWDP work together to maintain the proper weight distribution and ensure that the drill bit operates efficiently. These components help minimize drill string vibrations and ensure smooth operations, particularly in deep or difficult wells.
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