Spiral Drill Collars Size and Application

Date:2024-10-30Tags:drill pipe, drill bit

The spiral drill collar is an important component of the bottom of the drill string and the core component of the lower drilling assembly (BHA), usually located above the drill bit. As a thick-walled pipe, the wall thickness of the drill collar is about 38 to 53 mm, which is 4 to 6 times the wall thickness of the conventional drill pipe, so it has considerable weight and rigidity. Its main functions include applying drilling pressure, reducing drill bit vibration, and controlling well inclination. In the design of the drill collar, the hanging card groove and the slip groove are usually processed on the outer surface of the internal thread to facilitate the connection and disassembly operation when drilling or pulling out of the hole.

1. Classification of drill collars

Depending on the structure and material, drill collars can be divided into three types: integral drill collars, spiral drill collars and non-magnetic drill collars:
Integral drill collar
The integral drill collar is a smooth thick-walled round tube with connecting threads processed at both ends and no other special structure. Its main function is to increase the weight so that the drill bit can obtain stable drilling pressure during drilling and ensure the smooth progress of drilling operations.
Spiral Drill Collar
A spiral drill collar is a drill collar with three right-hand spiral grooves machined on the outer cylindrical surface of the integral drill collar, usually manufactured according to API Spec 7-1 and SY5144-2007 standards. The spiral groove is designed to reduce the contact area between the drill collar and the well wall, thereby reducing the friction of the well wall and reducing the phenomenon of drill sticking caused by differential pressure.
Specification size: In the outer diameter range of 3 3/8" to 11", the depth of the spiral groove is usually 7.9±1.59 mm, and the lead is 1168±25.4 mm, which is suitable for drilling environments with different well diameters.
Joint structure: A smooth section of 305-560 mm is left at the external thread end, and a grooveless section of 457-610 mm is left at the internal thread end, which is convenient for connection and shackle operations.
Non-magnetic drill collar
The non-magnetic drill collar is structurally the same as the integral drill collar, but is forged with N1310 low-carbon alloy steel to reduce magnetic interference. After strict control of chemical composition and mechanical property testing, the material can ensure its low magnetic permeability, good corrosion resistance, and qualified hardness and toughness. Non-magnetic drill collars are mainly used in measurement and monitoring operations in oil drilling to ensure the accuracy of measurement data during drilling.


2. Characteristics and applications of spiral drill collars

Spiral drill collars are a type of drill collar that is widely used in the drilling process. The main features are as follows:
A. Reduce the risk of stuck drill
The design of the spiral groove can significantly reduce the contact area between the drill collar and the well wall, allowing the mud to flow freely around the drill collar, balancing the pressure difference between the well wall and the drill collar, and preventing the phenomenon of stuck drill caused by the pressure difference. Especially in directional and inclined well drilling, spiral drill collars effectively reduce the possibility of well wall adsorption and stuck drill by reducing contact with the well wall.
B. Improve downhole stability
By reducing the pressure difference stuck drill, the spiral drill collar not only protects the drill tool, but also ensures the continuity of drilling work, reducing downtime and maintenance costs caused by stuck drill.
C. Structure and weight optimization
Compared with the same size of the whole drill collar, the spiral drill collar is slightly lighter (about 4% less) due to the presence of the spiral groove. This optimization reduces the total weight of the lower end of the drill string and helps maintain the overall balance of the drill string.


3. Production standards for spiral drill collars

Spiral drill collars are usually produced in accordance with international and industry standards. The main standards include:
API Spec 7-1: Provides basic production specifications for drill collars to ensure that they meet international standards in terms of strength, size, tolerance, etc.
SY5144-2007: This is a Chinese national standard that makes detailed provisions for the selection of drill collar materials, threaded connection requirements, etc., to ensure the stability and durability of drill collars in underground work.

Spiral Drill Collars

4. Application examples of spiral drill collars

BI-type drill collar
Uses three right-hand spiral grooves, with an outer diameter of 165.1 to 177.8 mm (6 1/2 to 7 inches), a spiral groove depth of 7.9±1.59 mm, and a lead of 1168±25.4 mm, which is suitable for drilling medium-sized wells.

BII-type drill collar
The outer diameter is 171.5 mm (6 3/4 inches), the cutting depth is 7.1 mm, and the lead is 1000±25.4 mm. Its shape curve equation is defined as a function of the polar diameter ρ, polar angle θ, radius R and coefficient e, and is used in more complex wellbore environments.

5. The main role of spiral drill collars

During the drilling process, drill collars have the following key functions:
Provide drilling pressure for the drill bit
The drill collar applies downward pressure to the drill bit through its own weight to ensure the efficiency of the drill bit in cutting the rock formation.
Maintain drill string strength
In high pressure or extrusion environments, the thick-walled structure of the drill collar gives it a high compressive strength, ensuring the stability of the entire drill string.
Reduce drill bit vibration
The drill collar has good rigidity and can effectively reduce the vibration, swing and jump of the drill bit, thereby ensuring the smoothness of the drilling process.
Control well inclination
By rationally configuring the number and position of the drill collar, the downhole trajectory can be effectively controlled to ensure the linearity and directional stability of the wellbore.


Spiral Drill Collars Size

Drill Collars

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

6.Conclusion

Spiral drill collars are an indispensable part of drilling engineering. Their design rationality and functionality not only directly affect drilling efficiency, but are also important factors in ensuring drilling safety. Compared with integral drill collars, spiral drill collars are superior in reducing the contact area between stuck drill and well wall, making them popular in actual operations. Whether in directional drilling or conventional drilling, spiral drill collars have become a key tool to improve drilling efficiency and reduce construction risks due to their excellent structural design and performance.

We use cookies to offer a better browsing experience, analyze site traffic, and personalize content. By using this site, you agree to our use of cookies.

Accept
Decline