Makeup Loss
When lengths of casing are joined together to form a string or section, the overall length of the string is less than the sum of the individual joints. The reason that the completed string is less than the sum of the parts is the makeup loss at the couplings.
It is clear from Fig. 1.5 that the makeup loss per joint for a string made up to the powertight position is:
where:
lj = lengt h of pipe.
ljc = length of the casing with coupling.
Lc = length of the coupling.
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1Ш Jtrnm > |
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/j = length of pipe. 1 1
Ip = length of casing with coupling.
J = distance between end of casing in power tight position and the center of the coupling.
Ц = makeup loss.
Lc = length of the coupling.
Fig. 1.5: Makeup loss per joint of casing.
J = distance between the casing end in the power tight position and the coupling center.
Li = makeup loss.
Calculate the makeup loss per joint for a 9|-in.. N-80. 47 lb/ft casing with short threads and couplings. Also calculate the loss in a 10.000-ft well (ignore tension effects) and the additional length of madeup string required to reach true vertical depth (TVD). Express the answer in general terms of 1JC. the average length of the casing in feet of the tallied (measured) casing and then calculate the necessary makeup lengths for lJC = 21, 30 and 40 — assumed average lengths of Rl. R2 and R3 casing available.
For a casing complete with couplings, the length /K is the distance measured from the uncoupled end of the pipe to the outer face of the coupling at the opposite end, with the coupling made-up power-tight (API Spec. 5CT).
From Table 1.4, Lc = 7| in. and.7 = 0.500-in. Thus,
= 3.875 — 0.500 = 3.375 in.
“Based on Example. 2.1, Craft et al. (1962)
Table 1.4: Round-thread casing dimensions for long threads and couplings.
in. in. in. in.
4.1 TOC o "1-5" h z All 0.5 7
5 All 0.5 7.75
1.5 All 0.5 8
6.625 All 0.5 8.75
7 All 0.5 9
7.625 All 0.5 9.25
8.625 All 0.5 10
9.625 All 0.5 10.5
1 STD 5В 5 Spec 5CT
The number of joints in 1.000 ft of tallied casing is 1.000//JC and. therefore, the makeup loss in 1.000 ft is:
Makeup loss per 1,000 ft = 3.375 x 1.000//JC.
= 3.375//j, in.
= 3.375/(12/jr) ft
As tension effects are ignored this is the makeup loss in any 1.000-ft section.
If Ly is defined as the total casing required to make 1.000 ft of made-up. power — tight string, then:
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Finally, using the general form of the above equation in Lj. Table 1.5 can be produced to give the makeup loss in a 10.000-ft string.