Here the "Net Piston Effect" is shown.
Say Csg & Tbg pressure changes are:
dPcp = 500 psi (often given as pre-post job csg pressure).
dPtp = 3,000 psi (often calculated by hydrostatic).
Packer, Tbg, & Csg areas: Apb, Ati, Ato = 7.1, 7.0, 9.2 sq in (given or from dia).
The packer (7.1) is larger than tbg id (7); so the GB predicts a negative (up) force:
Fp = dPCp(Apb-Ato) - dPTp(Apb - Ati)
Fp = 500(7.1-9.2)-3,000(7.1 - 7.0) = -1,385 lbf (up).
Fp = 500(-2.1) - 3,000(0.1)
Fp = -1,050-300 = -1,385
Fp = 500(7.1-7) - 3,000(7.1-9.2) = -1,385 lbf (up). This checks.
To calculate tbg length change? Say the tubing is 10,000'; tbg area is 9.2 - 7 = 1.8 sq in:
LtF/EAt = (10,000 ft*1,385 lbf)/(30M*1.8) = 0.15'*12 = -1.8 inches (up)
The entire tubing move section is a single page, with all the variables listed to the right.
Can you please Clarify what dPtp is? Is it Just Hydrostatic in the tubing? or Final Tubing P - Hydrostatic in the tubing
ReplyDeleteDefined on 6 DTC 9 and matches the value shown. Check?
DeleteCan you please clarify when to use Hooke's law of LtF/EAt and the eq on 6 DTC 9? delLf=Ft(L)SC?
ReplyDeleteWhat do you mean? You can use it whenever you want, right?
DeleteThe SPE reference has the formula for dF swapped around with regards to the annular and tubing pressure, which gives you a positive dF instead of negative....the magnitude is correct, but just wondering if a particular scenario would require flipping the sign of casing and tubing pressure changes?
ReplyDeleteWhat page on the SPE reference are you referring to, and what page on the Guidebook? Could you give specific equations with page numbers? It gets confusing, and I did this years ago :-)
DeleteHi David, I'm struggling with the calculations -1,050-300 = -1,350 not -1385, 9.2 - 7 = 2.2 sq in not 1.8 sq in.
ReplyDeleteJust want to check to make sure I'm not missing anything.
Could you also tell me how this scenario looks like (PKRtbg id)? its easy to see the other two scenarios in your guidebook but I cannot picture this one.
(Fp = 500(7.1-7) - 3,000(7.1-9.2) = -1,385 lbf (up). This checks.) have you change the assumptions for diameters here? Why?
Thanks and Regards.
This is probably a typo on my part on the blog. I just looked and don't have any record of this outside of this blog; I think I just whipped it out as an example. BTW, I also have lost my 2005 SPE Exam; do you have a copy of this problem from that exam? This would probably give me a clue what I was trying to do here...:-).
DeleteThanks David for the reply. Unfortunately I dont have the 2005 SPE Exam. I will look around and pass it on if I find it.
DeleteBtw I usually do a practice session locally each year (to keep sharp :-)) but due to C19 not this year. But if any interest I could try to set something up for some folk online; if interested send me a gmail (mdavidgo).
Delete