When the drill string get stuck, there are several ways to free the string as using Jar (up and/or down), straight pull, working torque down, etc. Pulling stuck pipe with torque in the drill string is one of those technique which often utilize to free the stuck drill string. However, there are some concerns that you should know before doing this because torque in the string will reduce a tensile capacity of tubular. This is very important to read and understand the combined load chart (Torque‐Tension Graph) in order to determine the limitation before pulling the pipe.
For this example, we use 5” DP, S-135, NC50 (4-1/2” IF connection) to be a reference figure.
- Pipe Size and Weight: 5.000″ 19.50ppf 0.362″ wall IEU
- Pipe Grade: S-135
- Range: 2
- Tool Joint: 6.625″ X 3.250″ NC50
- Tool Joint 120,000 psi Material Yield Strength
- Premium class
You can find the specification sheet from this http://www.workstringsinternational.com/pdf/specs/drill_pipe/us/5.000in%200.362wall%20IEU%20S135%20NC50%20(6.625%20x%203.250%20TJ)%209P%2012B.pdf
Reference source – http://www.workstringsinternational.com
This is the combined load chart (Torque‐Tension Graph).
Figure 1 – Combined Load Chart for 5″DP, S135, NC50 (4-1/2 “IF)
No Torque in Drill String
Without torque, the pipe body tensile strength = 560,800 lb (Point A) and tool joint tensile strength = 1,25 million lbs (Point D). At this point, the weakest point is obviously pipe body. Point B and Point C represents tool joint tensile strength at minimum and maximum recommended make up torque, respectively.
Max Recommended Make-up Torque (ft-lbs) = 30,700 ft-lb
Min Recommended Make-up Torque (ft-lbs) = 25,600 ft-lb
A tool joint with make-up torque between min and max recommended make up torque will have tensile strength approximately of 1.1 million lbs.
Figure 2 – Combined Load Chart at Zero Torque
20,000 ft-lb Torque in Drillstring
Referring to Figure 3, the tensile capacity of pipe body is reduced to approximately 550,000 lb (Point A) but the tool joint tensile capacity is still the same value of approximately of 1.1 million lbs with make up torque between min and recommended make up torque (Point B and Point C).
Figure 3 – Combined Load Chart at 20,000 ft-lb Torque
30,000 ft-lb Torque in Drillstring
Referring to Figure 4, the tensile capacity of pipe body is reduced to approximately 500,000 lb (Point A) but the tool joint tensile capacity is still the same value of approximately of 1.1 million lbs with make up torque close to the recommended make up torque (Point C).
Figure 4 – Combined Load Chart at 30,000 ft-lb Torque
Torque in the drillstring reduces the tensile capacity of pipe body therefore it is very important to check the pipe limitation by analyzing the torque-tension chart before applying a combined load in the drillstring. Utilizing the combined load chart will tell you the limit and reduce risk of parting the string unintentionally.