Sunday, 5 November 2017

NOW IT IS EASY TO CALCULATE OVERPULL DRILLING & ITS MARGIN WITH EXCEL SHEET

Step By Step Learn How To Calculate Overpull Drilling Term With Calculator

OVERPULL DRILLING CALCULATION


What Is The Maximum Overpull in Drilling

The Maximum Overpull In Drilling is the maximum pull that can be exerted on stuck drill pipe without causing failure in the Drill String.

How To Calculate Maximum Overpull In Drilling 

The maximum overpull that can be exerted on stuck drill pipe shall not exceed 80% of the maximum tensile strength of the weakest grade Drill Pipe. In other words, you must know which is the lowest grade drill pipes then get its tensile strength then multiply it in 80% and this will be the maximum overpull you can reach while any kind of stuck.

The maximum pull for each crossover point must be calculated to determine the maximum pull that can be exerted on the Drill String. The calculation procedure is illustrated in the following example.

Assume the Drilling Bit at 14000 ft & the drilling Bottom Hole Assembly BHA would consist of the following:

                                                                    Section                 80% Tensile
Section                            Length, ft         Air weight, lb           Strength, lb
                                  
Bottom Hole Assembly       1200                150,000 lb
5€" Grade G Drill pipe          12,063             270,934 lb               443,066
5" Grade S Drill pipe           737                  17,245 lb                 569,656
                                         _________
                                           14,000 ft
1- we check the maximum overpull on the weakest drill pipes. The maximum overpull that can be exerted on the top of grade G drill pipes without exceeding 80% of Grade G tensile strength is 443,066 lb.

2- Now calculate the maximum overpull in drilling string that can be exerted on top of grade S drill pipes is, 

Max overpull = 80% of Tensile Strength + weight of Grade S Drill Pipes
Max overpull = 443,066 + 17245 = 460,311 lb.

Since 460,311 lb are less than 80% of the grade S tensile strength (569,656 lb), then it is safe to pull 460,311 lb. 

So when we pull 460,311 lb at the surface 
  • The pull exerted on top of Grade S DP is 460,311 lb. 
  • The pull exerted on top of Grade G DP is 460,311 minus the weight of grade S DP,
    or 460,311-17245 = 443,066 lb.

How To Calculate Margin Of Overpull In Drilling 


margin overpull drilling calculation

Margin of Overpull in drilling is the difference between the maximum overpull in the drilling string and the current weight of your drilling string. off course you shall consider the last recorded pick up weight as it is the weight of your Drill String.

Now, Let's convert all these words above to an equation

Margin Of Overpull = Ta – Th

Where
Tis the hook load (excluding top drive weight), lb.
Ta is the maximum allowable tensile strength, lb.

You can also calculate the drill string weight from this equation

Th= Drill String Weight x Buoyancy Factor (BF)

Where you can calculate the drill string weight from below equation

Drill String Weight  = (Lbha × Wbha) + (Ldc×Wdc+(Lhwdp × Whwdp) + (Ldp × Wdp

WbhaBottom Hole Assembly BHA weight 
Lbha =  bottom hole assembly length
Wdc= drill collar weight 
Ldc = drill collar length
Whwdp= heavy weight drill pipe weight 
Lhwdp = heavy weight drill pipe length
Wdp = drill pipe weight 
Ldp = drill pipe length

Buoyancy Factor (BF) = (65.5 – MWT) ÷ 65.5

Example On How To Calculate Margin Of Overpull In Drilling 

Determine the margin of overpull from the following information:

The drill string consists of the following equipment:
5” DP S-135, 4-1/2” IF connection, adjusted weight of 23.5 ppf = 8,000 ft
5” HWDP S-135, 4-1/2” IF connection, adjusted weight of 58 ppf = 900 ft
Mud motor and MWD weight = 20 Klb
Lenght of mud motor and MWD = 90 ft
Mud weight is 9.2 ppg
Tensile strength of 5” DP S-135 (premium class) = 436 Klb
Tensile strength of 5” HWDP S-135 (premium class) = 1,100 Klb
90% of tensile strength is allowed to pull without permission from town.

Solution


1- Calculate the maximum tension will happen at the surface 
5”DP will get the most tension when pulling and since only 90% of tensile strength is allowed. The allowable tensile (Ta) is as follows;
Ta = 0.9 x 436 = 392 Klb


2- Calculate the buoyancy factor
Buoyancy Factor (BF) = (65.5 – 9.2) ÷ 65.5
Buoyancy Factor (BF) = 0.86


3- Calculate The String Weight from the following equation:

Drill String Weight  = (Lbha × Wbha) + (Ldc×Wdc+(Lhwdp × Whwdp) + (Ldp × Wdp

Note: Weight of mud motor and MWD is given at 20 Klb.
Drill String Weight = (8,000 × 23.5) + (900 × 58) +  (20,000)
Drill String Weight = 260 Klb


4- Calculate Tension on surface (Th)

Th= Drill String Weight x Buoyancy Factor (BF)


Th = 260 × 0.86 = 223.8 klb


5- Calculate Margin Of Overpull

Margin Of Overpull = Ta – Th

Margin of over pull = 392 – 223.8 = 168.2 Klb

Margin Of OverPull Calculator

marging of overpull drilling calculator

Simple calculator for overpull drilling from oilfieldteam website.

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