Problem 66: The following 5.5-inch casing options are available for a 11,000 ft hole (the casing will be run empty into 11.5 lb/gal mud):
lb/ft Type $/ft.
14.0 J-55 6.50.
15.5 K-55 7.70.
17.0 K-55 8.80.
17.0 C-75 9.70.
20.0 N-80 10.30.
23.0 N-80 11.60.
Considering collapse, tension, and burst (use max. pressure of 5,000 psi) the most economical casing design option using safety factors of 1.25 (and ignoring buoyancy) will use mostly: (A) J-55 (B) K-75 (C) C-75 (D) N-80.
Use Guidebook 3 HYD 2. Also A Guide to Professional Registration for Petroleum Engineers, 6th Edition 1991 has a similar example. Steps:
1. Pb = 5,000(1.25) = 6,250 psi. Thus J-55, K-55 fail due to burst; others good.
2. pc at bottom of hole = 0.052(11.5 ppg)11,000 ft(1.25) = 8,223 psi.
3. The next least expensive csg is 17 lb/ft C-75 pc = 6,040 psi.
4. Max. set depth of next least expensive csg: 6040/[0.052(11.5)1.25 = 8,080 ft.
So C-75 used from surface to 8,080 ft; more than half of the 11,000 ft thus (C).
This is an ugly problem for two reasons: 1) 6 csg options to work through, and 2) multiple casings could be together (which means a lot of calculations for tension & burst). So you have to be smart about how you work it plus not fall into the trap that only one casing type must be used (which gives the wrong answer of (D).
Could we get a thread to discuss the upcoming exam with other 2018 test takers?
ReplyDeleteDave, could you please give more context how this problem is solved? I am looking on 3 HYD 2 of GB 2018 #3 and dont see any of the steps you are referring to.
ReplyDeleteThanks.
It's asking for "the most economic casing design option", not option[S]. This seems extremely vague and misleading, insinuating that you must choose only one. Are we to always assume that you will be considering running more than one type if the problem doesn't explicitly state it?
ReplyDeleteThe purpose of problems like this are to include as many "styles" of problem as possible into a single problem for time-conservation purposes, so the test taker will have seen as much as possible before they take the exam...and so to force the tester to move fast and get used to educated guesses, because my experience (and many of the folk I talked to) is I needed more of this type of practice. So, I wouldn't overthink things here; it's just practice, plus trying to get an understanding of how tricky both the problems and the wording can be. YMMV.
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