What is The Common Drill Pipes Lengths
The Drill String is made up of several sections of Drill Pipes. The term "stand" consists mainly from two or three drill pipes joints which will have a length around 60 to 90 feet . every joint of pipe, referred to as a "single". According to API, there are three ranges of drill pipes lengths ; R1, R2, and R3.
Range 1 (R1) is shortest in length, more common for sizing production tubing or Casing, and ranges from 18 to 22 ft.
Range 2 (R2) is considered the standard length for Drill Pipe and ranges from 27 to 31 ft.
Range 3 (R3) is common in Casing and also deployed in deep water drilling applications. The increased length decreases the number of tool joints in each stand of drill pipe. The fall back being that the load exerted on each tool joint is greater increasing wear and reducing the expected life of the drill pipe. R3 ranges from 38 to 45 ft.
How To Perform Drill Pipes Lengths Design
The total load exerted on the top joint of the drill pipe consists of
the buoyed weight of the drill pipe plus the buoyed weight of the bottom hole assembly (heavy-weight drill pipe plus drill collars) and the margin of overpull (MOP).
The MOP is the desired amount of load in excess of the buoyed weight of the drill string to account for hole drag and provide excess pull capacity in the event the drill string becomes stuck in the hole.
The amount of overpull ranges from 50,000 to 100,000 lb.
The design criterion can be expressed as,
L = length of DP, ft
W = Actual weight of drill pipe, lb/ft
Lc = length of drill collars, ft
Wc = weight of collars, lb/ft
LH = length of heavy weight drill pipe, ft
WH = weight of heavy weight drill pipe, lb/ft
MOP = Margin of overpull, lb
Bf = buoyancy factor
Y = minimum yield strength, lb
Solving above Eq for the maximum length of drill pipe that can be used,
If the Drill String consists of two sections of drill pipe of different grade and weight, then the maximum length of the second drill pipe section (top section) is,
L1 = length of first section of drill pipe (lower section), ft
W1 = actual weight of first section of drill pipe, lb/ft
L2 = length of second section of drill pipe, ft
W2 = actual weight of second section of drill pipe, lb/ft
Y2 = minimum tensile strength of second section of drill pipe (top section), lb.
In drill string design the pipe of the lowest grade (weakest) is placed on bottom. Each section of Drill Pipe is designed starting with the Bottom Hole Assembly BHA and working upwards. This design is checked at various depths, for often the most critical section of hole is not at TD, but further up the hole due to mud weight changes.