On Passing the Petroleum Professional Engineering Exam
Saturday, December 19, 2020
Well Control: 2021 #3
When drilling an oil well using a rig with a 850 bbl mud system a sand was encountered from 9,000 ft to 10,200 ft. Reservoir pressure was measured at 4,950 psi.
Drilling ahead with a 9.8 lbm/gal mud weight continued until 12,000 ft, at which time the ROP rapidly increased and a kick suspected so the well was shut in. Drillpipe pressure was recorded at 650 psi. Company policy requires a trip margin of 200 psi; the barite (sacks) needed is closest to: A) 700; B) 705; C) 710; D) 715.
Click the button for the answer, commentary, and the SPE Reference Guide pages sourced. Feel free to leave comments or questions.
This problem requires basic drilling knowledge, has three distinct steps with two tricks. But all the needed equations are provided in the SPE Reference. One factor not provided in the Reference is how a "trip margin" fits into the equations; you can explore this subject in TS12 or the Guidebook (3 HYD 5).
FP = (9.8*0.052*12,000)+650 = 6,765 psi. [SPE RG P41, P47]
Note how the first reservoir pressure is a red herring, but many get fooled by this sort of misdirection.
KWM = (6,765 psi + 200 psi)/(0.052 psi-ft/ppg*12,000 ft) = 11.162 ppg. [SPE RG P48]
Trip or kick margins (given in pressure here) can be in ppg as well (the Guidebook has a section on trip and kick margins; these are tricky and you won't get any help from the provided SPE Reference Guide).
Barite = [1470*((11.162-9.8)/(35-11.162))] = 83.989 sks/100 bbl = (84 sks/100 bbl)*(850 bbl)=714 sks. [SPE RG P45]
Never forget this equation uses per 100# sk/100 bbl. D) 715 sks.
A reader pointed out to me that I originally forgot to include 3 significant digits on this calculation (fixed above to not confuse anyone). The problem is set up so even if you drop your digits you still get the right answer D because that wasn't my focus here. But I can see how it was confusing.
Hello Dave, this question makes sense and we simply must remember the trip margin factoring into the question. However, how would we account if they specified a kick margin. If that was the case, would we subtract 200 psi as opposed to adding it in the KMW equation if we were told to use a kick margin instead of a trip margin? Thanks.
A reader pointed out to me that I originally forgot to include 3 significant digits on this calculation (fixed above to not confuse anyone). The problem is set up so even if you drop your digits you still get the right answer D because that wasn't my focus here. But I can see how it was confusing.
ReplyDeleteThank you,
DeleteAndres
is comes out to 735 sx ?
ReplyDeleteyou mean if using 11.2 rather than 11.162?
Deleteusing 11.162 gave me (83.989 sx/100bbl)*850 bbl = 714 sx or using 11.2 got it (86.5 sx/100 bbl)*850 bbl = 735 sx
ReplyDeleteAll good...I'm having technical issues with the new "answer" button so bear with me :-).
DeleteHello Dave, this question makes sense and we simply must remember the trip margin factoring into the question. However, how would we account if they specified a kick margin. If that was the case, would we subtract 200 psi as opposed to adding it in the KMW equation if we were told to use a kick margin instead of a trip margin? Thanks.
ReplyDelete