Problem 12. ...balanced cement plug 50 ft above and below perf...10% excess...volume of displacement...: (A) 30, (B) 31, (C) 32, (D) 33 bbl.
First, note what is asked: displacement volume (that is, mud volume behind plug). Nothing more.
Next, organize data & your mind: 7" CSG, plug 3,500 - 4,000 ft. Use 3.5" TBG to pump.
Run your eye down the Guidebook cover to "Cement". "Plug" is on pg 5 CMT 6. It has 5 steps:
1) Redbook for CSG, ANN, TBG cf/ft (0.22, 0.154 & 0.0488). Note on the CBT the Redbook data would merely be given on the problem. Don't think just because these resources are not available to bring to the exam they won't need to be "looked up" on tables. In fact, I could imagine the tables being all grainy and hard to read.
2) Vplug slurry calc: 500 ft plug(0.22 cf/ft) = 110 cf.
3) Plug height w/ TBG in hole: Vplug/(Cann + Ctbg) = 110 cf/(0.154 + 0.0488 cf/ft) = 540 ft.
4) Displacement height: 4,000 - 540 = 3,460 ft (total - plug height w/ TBG in hole = mud height).
5) Displacement volume: 3,460(0.0488 cf/ft) = 169 cf = 30 bbl. Add 10% excess: 3 bbl for 33 bbl.
This is quick if you follow the 5 steps. But beware: there are a million ways to go wrong, both in the question wording and calculations! I just whipped this one out randomly in under 6 minutes like everyone else must on an exam so it wouldn't surprise me if I had an error lurking. Get used to doing these problems fast: the pace you practice is how you will test, and you won't get every one correct.
Where is the .154 coming from?
ReplyDelete7" csg x 3.5" annulus 0.154 cf/ft (Redbook S221 P85). Check?
DeleteGot it! Didn't have my hands on the redbook at the time
DeleteIn the kindle version, the tubing is 3.5", 9.3"...do you mean 9.3#/ft?
ReplyDeleteYes, this typo is fixed on new downloads; I'll put a note in the blog post, thanks!
DeleteOne more question--why is 4000' used for the total depth vs 3500'?
ReplyDeletePlug 50 ft below perfs. Perfs to 3,950 ft.
Delete3,950 + 50 = 4,000 ft. Check?
Yep, so my tubing is run to the bottom of the plug then?
DeleteTbg end defines plug bottom (pumping down tbg & up ann) right? Or am I on the wrong problem?
DeleteHello Dave, how would one go about solving this problem using the updated SPE guide book? There isn't any equation similar to the ones used in steps 2-5 in the Drilling -> Cement section? Any ideas on how to go about this or would a question like these not be fair game for the new CBT exam? Thanks.
ReplyDeleteGreat Q, I haven't really thought about this one using the RG. I bet there is a clever way to test one's knowledge here, but I haven't heard anyone post-exam asking me to update anything, so I would just be familiar with it but not overly focused. Please let me know if yous see anything in the RG related or that can be used to squeeze out some calcs here (I'm away from home right now so I can't look and my memory says no, but I've missed clever workarounds before.
Delete